PC5271 wiki - User contributions [en]

Optical Sensor for Noise Flickering

2024-04-17T04:02:13Z

Amanda: /* Other Light Source(s) */

==Group Members==
Eric Cheung Jun Hao; Lee An Min, Amanda; Loh Jia Ying Whitney

==Introduction and Background==
Flicker is the repeated and frequent variation in the output of light source over time. All light sources flicker but vary depending on several variables [1].

There are 4 features that have serious impact on the viewer [1]:

(1) Frequency

(2) Amplitude

(3) Wave form

(4) Light Intensity

The flicker effects can have adverse effects that impacts users as summarised by Wilkins in Table 1 [2]. As such, it is important to be able to detect frequencies when LED or sources of light fall within this range that can severely affect human functions, especially with the technological developments and the use of such technology.

''Table 1: Flicker and its Biological Effects [2]''

[[image:Flicker_Bio_effect.jpeg]]

==Objective==

The objective of this project is to characterise a given photodiode and to successfully determine the frequency of an unknown flickering light source.

[[image:Optical_sensor_circuit.jpeg | 300px | none | left ]]
''Figure 1: Potential Divider Circuit''

With a simple potential divider, consisting a resistor and a photodiode in series, the resistance and hence sensitivity of the photodiode can be determined. The photodiode resistance is a function of light exposure, more specifically it is inversely proportional to light intensity. By exposing the photodiode to visual noise tags, such as the flickering of LEDs, the resistance across the photodiode is expected to decrease and hence, a larger potential can be measured across the resistor. The output can be observed on an oscilloscope to determine the performance of the photodiode.

==Set-Up==
===Equipment Needed===

''Table 2: List of Equipment Needed''
{| class="wikitable" style="margin:auto" |
! S/N !! Item !! Description/Model No.
|-
| 1 || Soldering Iron || -
|-
| 2 || Soldering Tin || -
|-
| 3 || Wires || -
|-
| 4 || Resistors || 10k, 100k, 1M
|-
| 5 || Photodiode || Hamamatsu S5972
|-
| 6 || DC Power Supply || Matrix MPS-3005L-3
|-
| 7 || Signal Generator || Agilent 33220A
|-
| 8 || 2GHz Digital Oscilloscope || LeCroy WaveRunner 203MXi-A
|}

''Table 3: Colour, Wavelength, and Size of LEDs Used''
{| class="wikitable" style="margin:auto" |
! LED S/N !! Colour !! Wavelength (nm) !! Size (mm)
|-
| 1 || Red || 643 || 5
|-
| 2 || Amber || 605 || 5
|-
| 3 || Green || 570 || 5
|-
| 4 || Blue || 450-495 || 5
|}

===Experimental Set-up===
Characterization of the photodiode is done with three 5 mm LEDs: (i) red, 643nm; (ii) green, 570nm; and (iii) blue, 450nm to 495nm. It can be noted that the photodiode sensitivity increases with increasing wavelength of LED used.

The photodiode used in this experiment is Hamamatsu S5972 Si PIN photodiode. According to the datasheet, it has a spectral response range between 320nm to 1000nm, with a peak sensitivity at 800nm, near-infrared radiation. The cutoff frequency is 0.5GHz at a reverse bias of 10V. The terminal capacitance at a reverse bias of 2V is close to 3pF.

[[image: Optical_sensor_complete_setup.jpeg|500px]][[image: Optical_sensor_setup_closeup.jpeg|500px]]

''Figure 2: Experimental set-up (a) wide view, and (b) close-up view''

A signal generator is used to pulse the LEDs to create a flickering light source. A square wave with a peak-to-peak voltage of 2V is used across all the measurements taken. A DC power supply is used to supply 3V across the photodiode.

The performance of the photodiode will be determined by varying the following parameters: (i) wavelength of LED; (ii) external resistor in circuit; and (iii) frequency of LED blinking (1Hz - 100kHz).

The dependent variable that will be measured is the voltage reading across the external resistor.

This will allow us to determine the response of the photodiode and its efficiency (rise time) of photodiode at different wavelengths.

==Timeline and Milestone==

''Table 4: Timeline and Goals to Achieve''
{| class="wikitable" style="margin:auto"
! Week !! Dates !! Tasks
|-
| Week 7 || 4 - 8 Mar || Collecting equipment and prelimary set-up
|-
| Week 8 || 11 - 15 Mar || Complete circuit set-up and prelimary measurements
|-
| Week 9 || 18 - 22 Mar || Data collection (vary LEDs)
|-
| Week 10 || 25 - 29 Mar [Well-being day (28 Mar), Good Friday (29 Mar)]|| Data collection (vary resistance)
|-
| Week 11 || 1 - 5 Apr || Data Analysis and further measurements (if needed)
|-
| Week 12 || 8 - 12 Apr [Hari Raya (10 Apr)] || Data Analysis and explore other light sources (phone/computer screens)
|-
| Week 13 || 15 - 19 Apr || Analyse experimental results and complete documentation
|}

==Results==

===Varying External Resistance===

'''Relationship between resistance and cut-off frequency'''

It can be concluded that as external resistance increases, the cutoff frequency decreases. Decreasing the external resistance by one order of magnitude will increase the cut-off frequency by an order of magnitude. Hence, lower resistance needs to be used in order to measure at higher frequencies.

Comparing the results for red LED,

''Table 5: Cutoff frequency of red LED for different resistance values''
{| class="wikitable" style="margin:auto"
! Resistance (Ω) !! Cutoff Frequency (kHz)!! Reasoning
|-
| 10k || 100 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=10kHz but not at 100kHz. Based on a rise time of approximately 0.01ms, the cutoff frequency can be estimated to be close to 100kHz.
|-
| 100k || 33 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=10kHz but not at 100kHz. Based on a rise time of approximately 0.03ms, the cutoff frequency can be estimated to be close to 30kHz.
|-
| 1M || 6 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=1kHz but not at 10kHz. Based on a rise time of approximately 0.15ms, the cutoff frequency can be estimated to be close to 7kHz.
|}

[[image: Optical_sensor_red.png|1000px|centre]]
''Figure 3: Signal obtained for red LED with different resistance values''

Repeating the same analysis for the blue LED,

''Table 6: Cutoff frequency of blue LED for different resistance values''
{| class="wikitable" style="margin:auto"
! Resistance (Ω) !! Cutoff Frequency (kHz)!! Reasoning
|-
| 10k || 500 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=10kHz but not at 100kHz. Based on a rise time of approximately 0.003ms, the cutoff frequency can be estimated to be ~300kHz.
|-
| 100k || 14 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=10kHz but not at 100kHz. Based on a rise time of approximately 0.04ms, the cutoff frequency can be estimated to be ~25kHz.
|-
| 1M || 6 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=1kHz but not at 10kHz. Based on a rise time of approximately 0.20ms, the cutoff frequency can be estimated to be close to 5kHz.
|}

[[image: Optical_sensor_blue.png|1000px|centre]]
''Figure 4: Signal obtained for blue LED with different resistance values''

Narrowing down to the specific frequency of 1kHz for blue LED for a clearer illustration, it can be shown that with decreasing external resistance, time constant decreases which replicates the signal sent into the LED (square wave). However, a lower resistance will entail lower signal-to-noise ratio. At the lower resistance of 10kΩ, the signal captured resembles a square wave while the higher resistance of 1MΩ shows, there is an evident decay in the rise and fall of the captured signal. Furthermore, the graphs also illustrate that the background noise is more prominent at lower resistance as the steady-state value across the lower resistance is smaller.

[[image: compare_resistance_blue_1kHz.png|400px|centre]]
''Figure 5: Comparison of signal obtained for blue LED at fixed frequency of 1kHz for different resistance values, illustrating that time constant decreases with decreasing resistance''

For completeness of our discussion, the plots obtained from the measurements of the green LED is shown below. However, due to the low steady-state value of the voltage across the resistor, the rise time of the photodiode cannot be clearly determined.

[[image: Optical_sensor_green.png|1000px|centre]]
''Figure 6: Signal obtained for green LED with different resistance values''

===Varying Wavelength===

From our experimental results, the photodiode has a faster response at longer wavelengths.

''Table 7: Response time of photodiode based on wavelength''
{| class="wikitable" style="margin:auto"
! LED!! Wavelength (nm) !! Resistance (Ω) !! Rise Time (ms) !! Remarks
|-
| Red || 643 ||10k || 0.01 ||
|-
| || || 100k || 0.03 ||
|-
| || || 1M || 0.16 ||
|-
| Green || 570 || 10k, 100k, 1M || N.A. || Low signal-to-noise ratio
|-
| Blue|| 450-495 || 10k || 0.002 ||
|-
| || || 100k || 0.07 ||
|-
| || || 1M || 0.18
|}

Out of the three LEDs used, the signal-to-noise ratio of the green LED is the lowest. Powering the three LEDs reveals that with the same voltage supplied, the green LED is the dimmest. Thus, the intensity of incident green light on the photodiode is significantly lower. The signal captured by the photodiode is lower and hence, the decrease in resistance of the photodiode is smaller. As a result, the voltage across the external resistor in the circuit of a fixed resistance is lower. Because of this, the change in voltage reading (in the switching of the LED) on the oscilloscope is closer to background noise. Thus, signal-to-noise ratio is lower.

[[image: LED_brightness.jpeg|300px|centre]]
''Figure 7: Comparison of light intensity of different coloured LEDs''

Considering LEDs flickering at 100Hz, the following steady-state values for voltage across the external resistor were obtained.

For the Red LED,

''Table 8: Steady-state values for voltage for red LED''
{| class="wikitable" style="margin:auto"
! Resistance (Ω)!! Steady State Value (V)
|-
| 10k || 0.03
|-
| 100k || 0.40
|-
| 1M|| 2.16
|}

For the Blue LED,

''Table 9: Steady-state values for voltage for blue LED''
{| class="wikitable" style="margin:auto"
! Resistance (Ω)!! Steady State Value (V)
|-
| 10k || 0.05
|-
| 100k || 0.47
|-
| 1M|| 2.44
|}

The steady-state value is dependent on the photosensitivity at different wavelengths and the brightness of the LED.

===Other Light Source(s)===
The photodiode is used to characterise the flickering of a computer screen. For this, we choose the 100kΩ resistor that gave us a sufficient characteristics and designed a compact circuit.

[[image:Final_design.jpeg|400px|center]]
''Figure 8: Electronic configuration of photodiode on PCB''

Using the photodiode, we can determine that the Red LED was flickering at 1kHz, while the refresh rate of the computer screen was approximately 50kHz.

[[image:Flicker sources.png|400px|center]]
''Figure 9: Signal of light sources: red LED, laptop white screen, and laptop black screen''

==[[Lab Log]]==

==References==
[1] NVC Lighting UK, Technical Support - What is Flicker in Relation to Lighting? https://www.nvcuk.com/technical-support/view/what-is-flicker-in-relation-to-lighting-2

[2] A. Wilkins, J. Veitch & B. Lehman. “LED lighting flicker and potential health concerns: IEEE standard PAR1789 update, “Energy Conversion Congress and Exposition, Atlanta Georgia, pp. 171-178, 2010

Optical Sensor for Noise Flickering

2024-04-17T04:01:24Z

Amanda: /* Other Light Source(s) */

==Group Members==
Eric Cheung Jun Hao; Lee An Min, Amanda; Loh Jia Ying Whitney

==Introduction and Background==
Flicker is the repeated and frequent variation in the output of light source over time. All light sources flicker but vary depending on several variables [1].

There are 4 features that have serious impact on the viewer [1]:

(1) Frequency

(2) Amplitude

(3) Wave form

(4) Light Intensity

The flicker effects can have adverse effects that impacts users as summarised by Wilkins in Table 1 [2]. As such, it is important to be able to detect frequencies when LED or sources of light fall within this range that can severely affect human functions, especially with the technological developments and the use of such technology.

''Table 1: Flicker and its Biological Effects [2]''

[[image:Flicker_Bio_effect.jpeg]]

==Objective==

The objective of this project is to characterise a given photodiode and to successfully determine the frequency of an unknown flickering light source.

[[image:Optical_sensor_circuit.jpeg | 300px | none | left ]]
''Figure 1: Potential Divider Circuit''

With a simple potential divider, consisting a resistor and a photodiode in series, the resistance and hence sensitivity of the photodiode can be determined. The photodiode resistance is a function of light exposure, more specifically it is inversely proportional to light intensity. By exposing the photodiode to visual noise tags, such as the flickering of LEDs, the resistance across the photodiode is expected to decrease and hence, a larger potential can be measured across the resistor. The output can be observed on an oscilloscope to determine the performance of the photodiode.

==Set-Up==
===Equipment Needed===

''Table 2: List of Equipment Needed''
{| class="wikitable" style="margin:auto" |
! S/N !! Item !! Description/Model No.
|-
| 1 || Soldering Iron || -
|-
| 2 || Soldering Tin || -
|-
| 3 || Wires || -
|-
| 4 || Resistors || 10k, 100k, 1M
|-
| 5 || Photodiode || Hamamatsu S5972
|-
| 6 || DC Power Supply || Matrix MPS-3005L-3
|-
| 7 || Signal Generator || Agilent 33220A
|-
| 8 || 2GHz Digital Oscilloscope || LeCroy WaveRunner 203MXi-A
|}

''Table 3: Colour, Wavelength, and Size of LEDs Used''
{| class="wikitable" style="margin:auto" |
! LED S/N !! Colour !! Wavelength (nm) !! Size (mm)
|-
| 1 || Red || 643 || 5
|-
| 2 || Amber || 605 || 5
|-
| 3 || Green || 570 || 5
|-
| 4 || Blue || 450-495 || 5
|}

===Experimental Set-up===
Characterization of the photodiode is done with three 5 mm LEDs: (i) red, 643nm; (ii) green, 570nm; and (iii) blue, 450nm to 495nm. It can be noted that the photodiode sensitivity increases with increasing wavelength of LED used.

The photodiode used in this experiment is Hamamatsu S5972 Si PIN photodiode. According to the datasheet, it has a spectral response range between 320nm to 1000nm, with a peak sensitivity at 800nm, near-infrared radiation. The cutoff frequency is 0.5GHz at a reverse bias of 10V. The terminal capacitance at a reverse bias of 2V is close to 3pF.

[[image: Optical_sensor_complete_setup.jpeg|500px]][[image: Optical_sensor_setup_closeup.jpeg|500px]]

''Figure 2: Experimental set-up (a) wide view, and (b) close-up view''

A signal generator is used to pulse the LEDs to create a flickering light source. A square wave with a peak-to-peak voltage of 2V is used across all the measurements taken. A DC power supply is used to supply 3V across the photodiode.

The performance of the photodiode will be determined by varying the following parameters: (i) wavelength of LED; (ii) external resistor in circuit; and (iii) frequency of LED blinking (1Hz - 100kHz).

The dependent variable that will be measured is the voltage reading across the external resistor.

This will allow us to determine the response of the photodiode and its efficiency (rise time) of photodiode at different wavelengths.

==Timeline and Milestone==

''Table 4: Timeline and Goals to Achieve''
{| class="wikitable" style="margin:auto"
! Week !! Dates !! Tasks
|-
| Week 7 || 4 - 8 Mar || Collecting equipment and prelimary set-up
|-
| Week 8 || 11 - 15 Mar || Complete circuit set-up and prelimary measurements
|-
| Week 9 || 18 - 22 Mar || Data collection (vary LEDs)
|-
| Week 10 || 25 - 29 Mar [Well-being day (28 Mar), Good Friday (29 Mar)]|| Data collection (vary resistance)
|-
| Week 11 || 1 - 5 Apr || Data Analysis and further measurements (if needed)
|-
| Week 12 || 8 - 12 Apr [Hari Raya (10 Apr)] || Data Analysis and explore other light sources (phone/computer screens)
|-
| Week 13 || 15 - 19 Apr || Analyse experimental results and complete documentation
|}

==Results==

===Varying External Resistance===

'''Relationship between resistance and cut-off frequency'''

It can be concluded that as external resistance increases, the cutoff frequency decreases. Decreasing the external resistance by one order of magnitude will increase the cut-off frequency by an order of magnitude. Hence, lower resistance needs to be used in order to measure at higher frequencies.

Comparing the results for red LED,

''Table 5: Cutoff frequency of red LED for different resistance values''
{| class="wikitable" style="margin:auto"
! Resistance (Ω) !! Cutoff Frequency (kHz)!! Reasoning
|-
| 10k || 100 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=10kHz but not at 100kHz. Based on a rise time of approximately 0.01ms, the cutoff frequency can be estimated to be close to 100kHz.
|-
| 100k || 33 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=10kHz but not at 100kHz. Based on a rise time of approximately 0.03ms, the cutoff frequency can be estimated to be close to 30kHz.
|-
| 1M || 6 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=1kHz but not at 10kHz. Based on a rise time of approximately 0.15ms, the cutoff frequency can be estimated to be close to 7kHz.
|}

[[image: Optical_sensor_red.png|1000px|centre]]
''Figure 3: Signal obtained for red LED with different resistance values''

Repeating the same analysis for the blue LED,

''Table 6: Cutoff frequency of blue LED for different resistance values''
{| class="wikitable" style="margin:auto"
! Resistance (Ω) !! Cutoff Frequency (kHz)!! Reasoning
|-
| 10k || 500 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=10kHz but not at 100kHz. Based on a rise time of approximately 0.003ms, the cutoff frequency can be estimated to be ~300kHz.
|-
| 100k || 14 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=10kHz but not at 100kHz. Based on a rise time of approximately 0.04ms, the cutoff frequency can be estimated to be ~25kHz.
|-
| 1M || 6 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=1kHz but not at 10kHz. Based on a rise time of approximately 0.20ms, the cutoff frequency can be estimated to be close to 5kHz.
|}

[[image: Optical_sensor_blue.png|1000px|centre]]
''Figure 4: Signal obtained for blue LED with different resistance values''

Narrowing down to the specific frequency of 1kHz for blue LED for a clearer illustration, it can be shown that with decreasing external resistance, time constant decreases which replicates the signal sent into the LED (square wave). However, a lower resistance will entail lower signal-to-noise ratio. At the lower resistance of 10kΩ, the signal captured resembles a square wave while the higher resistance of 1MΩ shows, there is an evident decay in the rise and fall of the captured signal. Furthermore, the graphs also illustrate that the background noise is more prominent at lower resistance as the steady-state value across the lower resistance is smaller.

[[image: compare_resistance_blue_1kHz.png|400px|centre]]
''Figure 5: Comparison of signal obtained for blue LED at fixed frequency of 1kHz for different resistance values, illustrating that time constant decreases with decreasing resistance''

For completeness of our discussion, the plots obtained from the measurements of the green LED is shown below. However, due to the low steady-state value of the voltage across the resistor, the rise time of the photodiode cannot be clearly determined.

[[image: Optical_sensor_green.png|1000px|centre]]
''Figure 6: Signal obtained for green LED with different resistance values''

===Varying Wavelength===

From our experimental results, the photodiode has a faster response at longer wavelengths.

''Table 7: Response time of photodiode based on wavelength''
{| class="wikitable" style="margin:auto"
! LED!! Wavelength (nm) !! Resistance (Ω) !! Rise Time (ms) !! Remarks
|-
| Red || 643 ||10k || 0.01 ||
|-
| || || 100k || 0.03 ||
|-
| || || 1M || 0.16 ||
|-
| Green || 570 || 10k, 100k, 1M || N.A. || Low signal-to-noise ratio
|-
| Blue|| 450-495 || 10k || 0.002 ||
|-
| || || 100k || 0.07 ||
|-
| || || 1M || 0.18
|}

Out of the three LEDs used, the signal-to-noise ratio of the green LED is the lowest. Powering the three LEDs reveals that with the same voltage supplied, the green LED is the dimmest. Thus, the intensity of incident green light on the photodiode is significantly lower. The signal captured by the photodiode is lower and hence, the decrease in resistance of the photodiode is smaller. As a result, the voltage across the external resistor in the circuit of a fixed resistance is lower. Because of this, the change in voltage reading (in the switching of the LED) on the oscilloscope is closer to background noise. Thus, signal-to-noise ratio is lower.

[[image: LED_brightness.jpeg|300px|centre]]
''Figure 7: Comparison of light intensity of different coloured LEDs''

Considering LEDs flickering at 100Hz, the following steady-state values for voltage across the external resistor were obtained.

For the Red LED,

''Table 8: Steady-state values for voltage for red LED''
{| class="wikitable" style="margin:auto"
! Resistance (Ω)!! Steady State Value (V)
|-
| 10k || 0.03
|-
| 100k || 0.40
|-
| 1M|| 2.16
|}

For the Blue LED,

''Table 9: Steady-state values for voltage for blue LED''
{| class="wikitable" style="margin:auto"
! Resistance (Ω)!! Steady State Value (V)
|-
| 10k || 0.05
|-
| 100k || 0.47
|-
| 1M|| 2.44
|}

The steady-state value is dependent on the photosensitivity at different wavelengths and the brightness of the LED.

===Other Light Source(s)===
The photodiode is used to characterise the flickering of a computer screen. For this, we choose the 100kΩ resistor that gave us a sufficient characteristics and designed a compact circuit.

[[image:Final_design.jpeg|400px|center]]
''Figure 8: Electronic configuration of photodiode on PCB''

Using the photodiode, we can determine that the Red LED was flickering at 1kHz, while the refresh rate of the computer screen was approximately 50kHz.

[[image:Flicker sources.png|400px|center]]
''Figure 9: Signal of computer white screen''

==[[Lab Log]]==

==References==
[1] NVC Lighting UK, Technical Support - What is Flicker in Relation to Lighting? https://www.nvcuk.com/technical-support/view/what-is-flicker-in-relation-to-lighting-2

[2] A. Wilkins, J. Veitch & B. Lehman. “LED lighting flicker and potential health concerns: IEEE standard PAR1789 update, “Energy Conversion Congress and Exposition, Atlanta Georgia, pp. 171-178, 2010

Optical Sensor for Noise Flickering

2024-04-17T04:00:22Z

Amanda: /* Varying Wavelength */

==Group Members==
Eric Cheung Jun Hao; Lee An Min, Amanda; Loh Jia Ying Whitney

==Introduction and Background==
Flicker is the repeated and frequent variation in the output of light source over time. All light sources flicker but vary depending on several variables [1].

There are 4 features that have serious impact on the viewer [1]:

(1) Frequency

(2) Amplitude

(3) Wave form

(4) Light Intensity

The flicker effects can have adverse effects that impacts users as summarised by Wilkins in Table 1 [2]. As such, it is important to be able to detect frequencies when LED or sources of light fall within this range that can severely affect human functions, especially with the technological developments and the use of such technology.

''Table 1: Flicker and its Biological Effects [2]''

[[image:Flicker_Bio_effect.jpeg]]

==Objective==

The objective of this project is to characterise a given photodiode and to successfully determine the frequency of an unknown flickering light source.

[[image:Optical_sensor_circuit.jpeg | 300px | none | left ]]
''Figure 1: Potential Divider Circuit''

With a simple potential divider, consisting a resistor and a photodiode in series, the resistance and hence sensitivity of the photodiode can be determined. The photodiode resistance is a function of light exposure, more specifically it is inversely proportional to light intensity. By exposing the photodiode to visual noise tags, such as the flickering of LEDs, the resistance across the photodiode is expected to decrease and hence, a larger potential can be measured across the resistor. The output can be observed on an oscilloscope to determine the performance of the photodiode.

==Set-Up==
===Equipment Needed===

''Table 2: List of Equipment Needed''
{| class="wikitable" style="margin:auto" |
! S/N !! Item !! Description/Model No.
|-
| 1 || Soldering Iron || -
|-
| 2 || Soldering Tin || -
|-
| 3 || Wires || -
|-
| 4 || Resistors || 10k, 100k, 1M
|-
| 5 || Photodiode || Hamamatsu S5972
|-
| 6 || DC Power Supply || Matrix MPS-3005L-3
|-
| 7 || Signal Generator || Agilent 33220A
|-
| 8 || 2GHz Digital Oscilloscope || LeCroy WaveRunner 203MXi-A
|}

''Table 3: Colour, Wavelength, and Size of LEDs Used''
{| class="wikitable" style="margin:auto" |
! LED S/N !! Colour !! Wavelength (nm) !! Size (mm)
|-
| 1 || Red || 643 || 5
|-
| 2 || Amber || 605 || 5
|-
| 3 || Green || 570 || 5
|-
| 4 || Blue || 450-495 || 5
|}

===Experimental Set-up===
Characterization of the photodiode is done with three 5 mm LEDs: (i) red, 643nm; (ii) green, 570nm; and (iii) blue, 450nm to 495nm. It can be noted that the photodiode sensitivity increases with increasing wavelength of LED used.

The photodiode used in this experiment is Hamamatsu S5972 Si PIN photodiode. According to the datasheet, it has a spectral response range between 320nm to 1000nm, with a peak sensitivity at 800nm, near-infrared radiation. The cutoff frequency is 0.5GHz at a reverse bias of 10V. The terminal capacitance at a reverse bias of 2V is close to 3pF.

[[image: Optical_sensor_complete_setup.jpeg|500px]][[image: Optical_sensor_setup_closeup.jpeg|500px]]

''Figure 2: Experimental set-up (a) wide view, and (b) close-up view''

A signal generator is used to pulse the LEDs to create a flickering light source. A square wave with a peak-to-peak voltage of 2V is used across all the measurements taken. A DC power supply is used to supply 3V across the photodiode.

The performance of the photodiode will be determined by varying the following parameters: (i) wavelength of LED; (ii) external resistor in circuit; and (iii) frequency of LED blinking (1Hz - 100kHz).

The dependent variable that will be measured is the voltage reading across the external resistor.

This will allow us to determine the response of the photodiode and its efficiency (rise time) of photodiode at different wavelengths.

==Timeline and Milestone==

''Table 4: Timeline and Goals to Achieve''
{| class="wikitable" style="margin:auto"
! Week !! Dates !! Tasks
|-
| Week 7 || 4 - 8 Mar || Collecting equipment and prelimary set-up
|-
| Week 8 || 11 - 15 Mar || Complete circuit set-up and prelimary measurements
|-
| Week 9 || 18 - 22 Mar || Data collection (vary LEDs)
|-
| Week 10 || 25 - 29 Mar [Well-being day (28 Mar), Good Friday (29 Mar)]|| Data collection (vary resistance)
|-
| Week 11 || 1 - 5 Apr || Data Analysis and further measurements (if needed)
|-
| Week 12 || 8 - 12 Apr [Hari Raya (10 Apr)] || Data Analysis and explore other light sources (phone/computer screens)
|-
| Week 13 || 15 - 19 Apr || Analyse experimental results and complete documentation
|}

==Results==

===Varying External Resistance===

'''Relationship between resistance and cut-off frequency'''

It can be concluded that as external resistance increases, the cutoff frequency decreases. Decreasing the external resistance by one order of magnitude will increase the cut-off frequency by an order of magnitude. Hence, lower resistance needs to be used in order to measure at higher frequencies.

Comparing the results for red LED,

''Table 5: Cutoff frequency of red LED for different resistance values''
{| class="wikitable" style="margin:auto"
! Resistance (Ω) !! Cutoff Frequency (kHz)!! Reasoning
|-
| 10k || 100 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=10kHz but not at 100kHz. Based on a rise time of approximately 0.01ms, the cutoff frequency can be estimated to be close to 100kHz.
|-
| 100k || 33 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=10kHz but not at 100kHz. Based on a rise time of approximately 0.03ms, the cutoff frequency can be estimated to be close to 30kHz.
|-
| 1M || 6 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=1kHz but not at 10kHz. Based on a rise time of approximately 0.15ms, the cutoff frequency can be estimated to be close to 7kHz.
|}

[[image: Optical_sensor_red.png|1000px|centre]]
''Figure 3: Signal obtained for red LED with different resistance values''

Repeating the same analysis for the blue LED,

''Table 6: Cutoff frequency of blue LED for different resistance values''
{| class="wikitable" style="margin:auto"
! Resistance (Ω) !! Cutoff Frequency (kHz)!! Reasoning
|-
| 10k || 500 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=10kHz but not at 100kHz. Based on a rise time of approximately 0.003ms, the cutoff frequency can be estimated to be ~300kHz.
|-
| 100k || 14 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=10kHz but not at 100kHz. Based on a rise time of approximately 0.04ms, the cutoff frequency can be estimated to be ~25kHz.
|-
| 1M || 6 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=1kHz but not at 10kHz. Based on a rise time of approximately 0.20ms, the cutoff frequency can be estimated to be close to 5kHz.
|}

[[image: Optical_sensor_blue.png|1000px|centre]]
''Figure 4: Signal obtained for blue LED with different resistance values''

Narrowing down to the specific frequency of 1kHz for blue LED for a clearer illustration, it can be shown that with decreasing external resistance, time constant decreases which replicates the signal sent into the LED (square wave). However, a lower resistance will entail lower signal-to-noise ratio. At the lower resistance of 10kΩ, the signal captured resembles a square wave while the higher resistance of 1MΩ shows, there is an evident decay in the rise and fall of the captured signal. Furthermore, the graphs also illustrate that the background noise is more prominent at lower resistance as the steady-state value across the lower resistance is smaller.

[[image: compare_resistance_blue_1kHz.png|400px|centre]]
''Figure 5: Comparison of signal obtained for blue LED at fixed frequency of 1kHz for different resistance values, illustrating that time constant decreases with decreasing resistance''

For completeness of our discussion, the plots obtained from the measurements of the green LED is shown below. However, due to the low steady-state value of the voltage across the resistor, the rise time of the photodiode cannot be clearly determined.

[[image: Optical_sensor_green.png|1000px|centre]]
''Figure 6: Signal obtained for green LED with different resistance values''

===Varying Wavelength===

From our experimental results, the photodiode has a faster response at longer wavelengths.

''Table 7: Response time of photodiode based on wavelength''
{| class="wikitable" style="margin:auto"
! LED!! Wavelength (nm) !! Resistance (Ω) !! Rise Time (ms) !! Remarks
|-
| Red || 643 ||10k || 0.01 ||
|-
| || || 100k || 0.03 ||
|-
| || || 1M || 0.16 ||
|-
| Green || 570 || 10k, 100k, 1M || N.A. || Low signal-to-noise ratio
|-
| Blue|| 450-495 || 10k || 0.002 ||
|-
| || || 100k || 0.07 ||
|-
| || || 1M || 0.18
|}

Out of the three LEDs used, the signal-to-noise ratio of the green LED is the lowest. Powering the three LEDs reveals that with the same voltage supplied, the green LED is the dimmest. Thus, the intensity of incident green light on the photodiode is significantly lower. The signal captured by the photodiode is lower and hence, the decrease in resistance of the photodiode is smaller. As a result, the voltage across the external resistor in the circuit of a fixed resistance is lower. Because of this, the change in voltage reading (in the switching of the LED) on the oscilloscope is closer to background noise. Thus, signal-to-noise ratio is lower.

[[image: LED_brightness.jpeg|300px|centre]]
''Figure 7: Comparison of light intensity of different coloured LEDs''

Considering LEDs flickering at 100Hz, the following steady-state values for voltage across the external resistor were obtained.

For the Red LED,

''Table 8: Steady-state values for voltage for red LED''
{| class="wikitable" style="margin:auto"
! Resistance (Ω)!! Steady State Value (V)
|-
| 10k || 0.03
|-
| 100k || 0.40
|-
| 1M|| 2.16
|}

For the Blue LED,

''Table 9: Steady-state values for voltage for blue LED''
{| class="wikitable" style="margin:auto"
! Resistance (Ω)!! Steady State Value (V)
|-
| 10k || 0.05
|-
| 100k || 0.47
|-
| 1M|| 2.44
|}

The steady-state value is dependent on the photosensitivity at different wavelengths and the brightness of the LED.

===Other Light Source(s)===
The photodiode is used to characterise the flickering of a computer screen. For this, we choose the 100kΩ resistor that gave us a sufficient characteristics and designed a compact circuit.

[[image:Final_design.jpeg|400px|center]]

Using the photodiode, we can determine that the Red LED was flickering at 1kHz, while the refresh rate of the computer screen was approximately 50kHz.
[[image:Flicker sources.png|400px|center]]

==[[Lab Log]]==

==References==
[1] NVC Lighting UK, Technical Support - What is Flicker in Relation to Lighting? https://www.nvcuk.com/technical-support/view/what-is-flicker-in-relation-to-lighting-2

[2] A. Wilkins, J. Veitch & B. Lehman. “LED lighting flicker and potential health concerns: IEEE standard PAR1789 update, “Energy Conversion Congress and Exposition, Atlanta Georgia, pp. 171-178, 2010

Optical Sensor for Noise Flickering

2024-04-17T03:59:41Z

Amanda: /* Varying Wavelength */

==Group Members==
Eric Cheung Jun Hao; Lee An Min, Amanda; Loh Jia Ying Whitney

==Introduction and Background==
Flicker is the repeated and frequent variation in the output of light source over time. All light sources flicker but vary depending on several variables [1].

There are 4 features that have serious impact on the viewer [1]:

(1) Frequency

(2) Amplitude

(3) Wave form

(4) Light Intensity

The flicker effects can have adverse effects that impacts users as summarised by Wilkins in Table 1 [2]. As such, it is important to be able to detect frequencies when LED or sources of light fall within this range that can severely affect human functions, especially with the technological developments and the use of such technology.

''Table 1: Flicker and its Biological Effects [2]''

[[image:Flicker_Bio_effect.jpeg]]

==Objective==

The objective of this project is to characterise a given photodiode and to successfully determine the frequency of an unknown flickering light source.

[[image:Optical_sensor_circuit.jpeg | 300px | none | left ]]
''Figure 1: Potential Divider Circuit''

With a simple potential divider, consisting a resistor and a photodiode in series, the resistance and hence sensitivity of the photodiode can be determined. The photodiode resistance is a function of light exposure, more specifically it is inversely proportional to light intensity. By exposing the photodiode to visual noise tags, such as the flickering of LEDs, the resistance across the photodiode is expected to decrease and hence, a larger potential can be measured across the resistor. The output can be observed on an oscilloscope to determine the performance of the photodiode.

==Set-Up==
===Equipment Needed===

''Table 2: List of Equipment Needed''
{| class="wikitable" style="margin:auto" |
! S/N !! Item !! Description/Model No.
|-
| 1 || Soldering Iron || -
|-
| 2 || Soldering Tin || -
|-
| 3 || Wires || -
|-
| 4 || Resistors || 10k, 100k, 1M
|-
| 5 || Photodiode || Hamamatsu S5972
|-
| 6 || DC Power Supply || Matrix MPS-3005L-3
|-
| 7 || Signal Generator || Agilent 33220A
|-
| 8 || 2GHz Digital Oscilloscope || LeCroy WaveRunner 203MXi-A
|}

''Table 3: Colour, Wavelength, and Size of LEDs Used''
{| class="wikitable" style="margin:auto" |
! LED S/N !! Colour !! Wavelength (nm) !! Size (mm)
|-
| 1 || Red || 643 || 5
|-
| 2 || Amber || 605 || 5
|-
| 3 || Green || 570 || 5
|-
| 4 || Blue || 450-495 || 5
|}

===Experimental Set-up===
Characterization of the photodiode is done with three 5 mm LEDs: (i) red, 643nm; (ii) green, 570nm; and (iii) blue, 450nm to 495nm. It can be noted that the photodiode sensitivity increases with increasing wavelength of LED used.

The photodiode used in this experiment is Hamamatsu S5972 Si PIN photodiode. According to the datasheet, it has a spectral response range between 320nm to 1000nm, with a peak sensitivity at 800nm, near-infrared radiation. The cutoff frequency is 0.5GHz at a reverse bias of 10V. The terminal capacitance at a reverse bias of 2V is close to 3pF.

[[image: Optical_sensor_complete_setup.jpeg|500px]][[image: Optical_sensor_setup_closeup.jpeg|500px]]

''Figure 2: Experimental set-up (a) wide view, and (b) close-up view''

A signal generator is used to pulse the LEDs to create a flickering light source. A square wave with a peak-to-peak voltage of 2V is used across all the measurements taken. A DC power supply is used to supply 3V across the photodiode.

The performance of the photodiode will be determined by varying the following parameters: (i) wavelength of LED; (ii) external resistor in circuit; and (iii) frequency of LED blinking (1Hz - 100kHz).

The dependent variable that will be measured is the voltage reading across the external resistor.

This will allow us to determine the response of the photodiode and its efficiency (rise time) of photodiode at different wavelengths.

==Timeline and Milestone==

''Table 4: Timeline and Goals to Achieve''
{| class="wikitable" style="margin:auto"
! Week !! Dates !! Tasks
|-
| Week 7 || 4 - 8 Mar || Collecting equipment and prelimary set-up
|-
| Week 8 || 11 - 15 Mar || Complete circuit set-up and prelimary measurements
|-
| Week 9 || 18 - 22 Mar || Data collection (vary LEDs)
|-
| Week 10 || 25 - 29 Mar [Well-being day (28 Mar), Good Friday (29 Mar)]|| Data collection (vary resistance)
|-
| Week 11 || 1 - 5 Apr || Data Analysis and further measurements (if needed)
|-
| Week 12 || 8 - 12 Apr [Hari Raya (10 Apr)] || Data Analysis and explore other light sources (phone/computer screens)
|-
| Week 13 || 15 - 19 Apr || Analyse experimental results and complete documentation
|}

==Results==

===Varying External Resistance===

'''Relationship between resistance and cut-off frequency'''

It can be concluded that as external resistance increases, the cutoff frequency decreases. Decreasing the external resistance by one order of magnitude will increase the cut-off frequency by an order of magnitude. Hence, lower resistance needs to be used in order to measure at higher frequencies.

Comparing the results for red LED,

''Table 5: Cutoff frequency of red LED for different resistance values''
{| class="wikitable" style="margin:auto"
! Resistance (Ω) !! Cutoff Frequency (kHz)!! Reasoning
|-
| 10k || 100 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=10kHz but not at 100kHz. Based on a rise time of approximately 0.01ms, the cutoff frequency can be estimated to be close to 100kHz.
|-
| 100k || 33 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=10kHz but not at 100kHz. Based on a rise time of approximately 0.03ms, the cutoff frequency can be estimated to be close to 30kHz.
|-
| 1M || 6 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=1kHz but not at 10kHz. Based on a rise time of approximately 0.15ms, the cutoff frequency can be estimated to be close to 7kHz.
|}

[[image: Optical_sensor_red.png|1000px|centre]]
''Figure 3: Signal obtained for red LED with different resistance values''

Repeating the same analysis for the blue LED,

''Table 6: Cutoff frequency of blue LED for different resistance values''
{| class="wikitable" style="margin:auto"
! Resistance (Ω) !! Cutoff Frequency (kHz)!! Reasoning
|-
| 10k || 500 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=10kHz but not at 100kHz. Based on a rise time of approximately 0.003ms, the cutoff frequency can be estimated to be ~300kHz.
|-
| 100k || 14 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=10kHz but not at 100kHz. Based on a rise time of approximately 0.04ms, the cutoff frequency can be estimated to be ~25kHz.
|-
| 1M || 6 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=1kHz but not at 10kHz. Based on a rise time of approximately 0.20ms, the cutoff frequency can be estimated to be close to 5kHz.
|}

[[image: Optical_sensor_blue.png|1000px|centre]]
''Figure 4: Signal obtained for blue LED with different resistance values''

Narrowing down to the specific frequency of 1kHz for blue LED for a clearer illustration, it can be shown that with decreasing external resistance, time constant decreases which replicates the signal sent into the LED (square wave). However, a lower resistance will entail lower signal-to-noise ratio. At the lower resistance of 10kΩ, the signal captured resembles a square wave while the higher resistance of 1MΩ shows, there is an evident decay in the rise and fall of the captured signal. Furthermore, the graphs also illustrate that the background noise is more prominent at lower resistance as the steady-state value across the lower resistance is smaller.

[[image: compare_resistance_blue_1kHz.png|400px|centre]]
''Figure 5: Comparison of signal obtained for blue LED at fixed frequency of 1kHz for different resistance values, illustrating that time constant decreases with decreasing resistance''

For completeness of our discussion, the plots obtained from the measurements of the green LED is shown below. However, due to the low steady-state value of the voltage across the resistor, the rise time of the photodiode cannot be clearly determined.

[[image: Optical_sensor_green.png|1000px|centre]]
''Figure 6: Signal obtained for green LED with different resistance values''

===Varying Wavelength===

From our experimental results, the photodiode has a faster response at longer wavelengths.

''Table 7: Response time of photodiode based on wavelength''
{| class="wikitable" style="margin:auto"
! LED!! Wavelength (nm) !! Resistance (Ω) !! Rise Time (ms) !! Remarks
|-
| Red || 643 ||10k || 0.01 ||
|-
| || || 100k || 0.03 ||
|-
| || || 1M || 0.16 ||
|-
| Green || 570 || 10k, 100k, 1M || N.A. || Low signal-to-noise ratio
|-
| Blue|| 450-495 || 10k || 0.002 ||
|-
| || || 100k || 0.07 ||
|-
| || || 1M || 0.18
|}

Out of the three LEDs used, the signal-to-noise ratio of the green LED is the lowest. Powering the three LEDs reveals that with the same voltage supplied, the green LED is the dimmest. Thus, the intensity of incident green light on the photodiode is significantly lower. The signal captured by the photodiode is lower and hence, the decrease in resistance of the photodiode is smaller. As a result, the voltage across the external resistor in the circuit of a fixed resistance is lower. Because of this, the change in voltage reading (in the switching of the LED) on the oscilloscope is closer to background noise. Thus, signal-to-noise ratio is lower.

[[image: LED_brightness.jpeg|300px|centre]]
''Figure 7: Comparison of light intensity of different coloured LEDs''

Considering LEDs flickering at 100Hz, the following steady-state values for voltage across the external resistor were obtained.

For the Red LED,
{| class="wikitable" style="margin:auto"
! Resistance (Ω)!! Steady State Value (V)
|-
| 10k || 0.03
|-
| 100k || 0.40
|-
| 1M|| 2.16
|}

For the Blue LED,
{| class="wikitable" style="margin:auto"
! Resistance (Ω)!! Steady State Value (V)
|-
| 10k || 0.05
|-
| 100k || 0.47
|-
| 1M|| 2.44
|}

The steady-state value is dependent on the photosensitivity at different wavelengths and the brightness of the LED.

===Other Light Source(s)===
The photodiode is used to characterise the flickering of a computer screen. For this, we choose the 100kΩ resistor that gave us a sufficient characteristics and designed a compact circuit.

[[image:Final_design.jpeg|400px|center]]

Using the photodiode, we can determine that the Red LED was flickering at 1kHz, while the refresh rate of the computer screen was approximately 50kHz.
[[image:Flicker sources.png|400px|center]]

==[[Lab Log]]==

==References==
[1] NVC Lighting UK, Technical Support - What is Flicker in Relation to Lighting? https://www.nvcuk.com/technical-support/view/what-is-flicker-in-relation-to-lighting-2

[2] A. Wilkins, J. Veitch & B. Lehman. “LED lighting flicker and potential health concerns: IEEE standard PAR1789 update, “Energy Conversion Congress and Exposition, Atlanta Georgia, pp. 171-178, 2010

Optical Sensor for Noise Flickering

2024-04-17T03:58:31Z

Amanda: /* Varying External Resistance */

==Group Members==
Eric Cheung Jun Hao; Lee An Min, Amanda; Loh Jia Ying Whitney

==Introduction and Background==
Flicker is the repeated and frequent variation in the output of light source over time. All light sources flicker but vary depending on several variables [1].

There are 4 features that have serious impact on the viewer [1]:

(1) Frequency

(2) Amplitude

(3) Wave form

(4) Light Intensity

The flicker effects can have adverse effects that impacts users as summarised by Wilkins in Table 1 [2]. As such, it is important to be able to detect frequencies when LED or sources of light fall within this range that can severely affect human functions, especially with the technological developments and the use of such technology.

''Table 1: Flicker and its Biological Effects [2]''

[[image:Flicker_Bio_effect.jpeg]]

==Objective==

The objective of this project is to characterise a given photodiode and to successfully determine the frequency of an unknown flickering light source.

[[image:Optical_sensor_circuit.jpeg | 300px | none | left ]]
''Figure 1: Potential Divider Circuit''

With a simple potential divider, consisting a resistor and a photodiode in series, the resistance and hence sensitivity of the photodiode can be determined. The photodiode resistance is a function of light exposure, more specifically it is inversely proportional to light intensity. By exposing the photodiode to visual noise tags, such as the flickering of LEDs, the resistance across the photodiode is expected to decrease and hence, a larger potential can be measured across the resistor. The output can be observed on an oscilloscope to determine the performance of the photodiode.

==Set-Up==
===Equipment Needed===

''Table 2: List of Equipment Needed''
{| class="wikitable" style="margin:auto" |
! S/N !! Item !! Description/Model No.
|-
| 1 || Soldering Iron || -
|-
| 2 || Soldering Tin || -
|-
| 3 || Wires || -
|-
| 4 || Resistors || 10k, 100k, 1M
|-
| 5 || Photodiode || Hamamatsu S5972
|-
| 6 || DC Power Supply || Matrix MPS-3005L-3
|-
| 7 || Signal Generator || Agilent 33220A
|-
| 8 || 2GHz Digital Oscilloscope || LeCroy WaveRunner 203MXi-A
|}

''Table 3: Colour, Wavelength, and Size of LEDs Used''
{| class="wikitable" style="margin:auto" |
! LED S/N !! Colour !! Wavelength (nm) !! Size (mm)
|-
| 1 || Red || 643 || 5
|-
| 2 || Amber || 605 || 5
|-
| 3 || Green || 570 || 5
|-
| 4 || Blue || 450-495 || 5
|}

===Experimental Set-up===
Characterization of the photodiode is done with three 5 mm LEDs: (i) red, 643nm; (ii) green, 570nm; and (iii) blue, 450nm to 495nm. It can be noted that the photodiode sensitivity increases with increasing wavelength of LED used.

The photodiode used in this experiment is Hamamatsu S5972 Si PIN photodiode. According to the datasheet, it has a spectral response range between 320nm to 1000nm, with a peak sensitivity at 800nm, near-infrared radiation. The cutoff frequency is 0.5GHz at a reverse bias of 10V. The terminal capacitance at a reverse bias of 2V is close to 3pF.

[[image: Optical_sensor_complete_setup.jpeg|500px]][[image: Optical_sensor_setup_closeup.jpeg|500px]]

''Figure 2: Experimental set-up (a) wide view, and (b) close-up view''

A signal generator is used to pulse the LEDs to create a flickering light source. A square wave with a peak-to-peak voltage of 2V is used across all the measurements taken. A DC power supply is used to supply 3V across the photodiode.

The performance of the photodiode will be determined by varying the following parameters: (i) wavelength of LED; (ii) external resistor in circuit; and (iii) frequency of LED blinking (1Hz - 100kHz).

The dependent variable that will be measured is the voltage reading across the external resistor.

This will allow us to determine the response of the photodiode and its efficiency (rise time) of photodiode at different wavelengths.

==Timeline and Milestone==

''Table 4: Timeline and Goals to Achieve''
{| class="wikitable" style="margin:auto"
! Week !! Dates !! Tasks
|-
| Week 7 || 4 - 8 Mar || Collecting equipment and prelimary set-up
|-
| Week 8 || 11 - 15 Mar || Complete circuit set-up and prelimary measurements
|-
| Week 9 || 18 - 22 Mar || Data collection (vary LEDs)
|-
| Week 10 || 25 - 29 Mar [Well-being day (28 Mar), Good Friday (29 Mar)]|| Data collection (vary resistance)
|-
| Week 11 || 1 - 5 Apr || Data Analysis and further measurements (if needed)
|-
| Week 12 || 8 - 12 Apr [Hari Raya (10 Apr)] || Data Analysis and explore other light sources (phone/computer screens)
|-
| Week 13 || 15 - 19 Apr || Analyse experimental results and complete documentation
|}

==Results==

===Varying External Resistance===

'''Relationship between resistance and cut-off frequency'''

It can be concluded that as external resistance increases, the cutoff frequency decreases. Decreasing the external resistance by one order of magnitude will increase the cut-off frequency by an order of magnitude. Hence, lower resistance needs to be used in order to measure at higher frequencies.

Comparing the results for red LED,

''Table 5: Cutoff frequency of red LED for different resistance values''
{| class="wikitable" style="margin:auto"
! Resistance (Ω) !! Cutoff Frequency (kHz)!! Reasoning
|-
| 10k || 100 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=10kHz but not at 100kHz. Based on a rise time of approximately 0.01ms, the cutoff frequency can be estimated to be close to 100kHz.
|-
| 100k || 33 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=10kHz but not at 100kHz. Based on a rise time of approximately 0.03ms, the cutoff frequency can be estimated to be close to 30kHz.
|-
| 1M || 6 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=1kHz but not at 10kHz. Based on a rise time of approximately 0.15ms, the cutoff frequency can be estimated to be close to 7kHz.
|}

[[image: Optical_sensor_red.png|1000px|centre]]
''Figure 3: Signal obtained for red LED with different resistance values''

Repeating the same analysis for the blue LED,

''Table 6: Cutoff frequency of blue LED for different resistance values''
{| class="wikitable" style="margin:auto"
! Resistance (Ω) !! Cutoff Frequency (kHz)!! Reasoning
|-
| 10k || 500 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=10kHz but not at 100kHz. Based on a rise time of approximately 0.003ms, the cutoff frequency can be estimated to be ~300kHz.
|-
| 100k || 14 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=10kHz but not at 100kHz. Based on a rise time of approximately 0.04ms, the cutoff frequency can be estimated to be ~25kHz.
|-
| 1M || 6 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=1kHz but not at 10kHz. Based on a rise time of approximately 0.20ms, the cutoff frequency can be estimated to be close to 5kHz.
|}

[[image: Optical_sensor_blue.png|1000px|centre]]
''Figure 4: Signal obtained for blue LED with different resistance values''

Narrowing down to the specific frequency of 1kHz for blue LED for a clearer illustration, it can be shown that with decreasing external resistance, time constant decreases which replicates the signal sent into the LED (square wave). However, a lower resistance will entail lower signal-to-noise ratio. At the lower resistance of 10kΩ, the signal captured resembles a square wave while the higher resistance of 1MΩ shows, there is an evident decay in the rise and fall of the captured signal. Furthermore, the graphs also illustrate that the background noise is more prominent at lower resistance as the steady-state value across the lower resistance is smaller.

[[image: compare_resistance_blue_1kHz.png|400px|centre]]
''Figure 5: Comparison of signal obtained for blue LED at fixed frequency of 1kHz for different resistance values, illustrating that time constant decreases with decreasing resistance''

For completeness of our discussion, the plots obtained from the measurements of the green LED is shown below. However, due to the low steady-state value of the voltage across the resistor, the rise time of the photodiode cannot be clearly determined.

[[image: Optical_sensor_green.png|1000px|centre]]
''Figure 6: Signal obtained for green LED with different resistance values''

===Varying Wavelength===

From our experimental results, the photodiode has a faster response at longer wavelengths.
{| class="wikitable" style="margin:auto"
! LED!! Wavelength (nm) !! Resistance (Ω) !! Rise Time (ms) !! Remarks
|-
| Red || 643 ||10k || 0.01 ||
|-
| || || 100k || 0.03 ||
|-
| || || 1M || 0.16 ||
|-
| Green || 570 || 10k, 100k, 1M || N.A. || Low signal-to-noise ratio
|-
| Blue|| 450-495 || 10k || 0.002 ||
|-
| || || 100k || 0.07 ||
|-
| || || 1M || 0.18
|}

Out of the three LEDs used, the signal-to-noise ratio of the green LED is the lowest. Powering the three LEDs reveals that with the same voltage supplied, the green LED is the dimmest. Thus, the intensity of incident green light on the photodiode is significantly lower. The signal captured by the photodiode is lower and hence, the decrease in resistance of the photodiode is smaller. As a result, the voltage across the external resistor in the circuit of a fixed resistance is lower. Because of this, the change in voltage reading (in the switching of the LED) on the oscilloscope is closer to background noise. Thus, signal-to-noise ratio is lower.

[[image: LED_brightness.jpeg|300px|centre]]

Considering LEDs flickering at 100Hz, the following steady-state values for voltage across the external resistor were obtained.

For the Red LED,
{| class="wikitable" style="margin:auto"
! Resistance (Ω)!! Steady State Value (V)
|-
| 10k || 0.03
|-
| 100k || 0.40
|-
| 1M|| 2.16
|}

For the Blue LED,
{| class="wikitable" style="margin:auto"
! Resistance (Ω)!! Steady State Value (V)
|-
| 10k || 0.05
|-
| 100k || 0.47
|-
| 1M|| 2.44
|}

The steady-state value is dependent on the photosensitivity at different wavelengths and the brightness of the LED.

===Other Light Source(s)===
The photodiode is used to characterise the flickering of a computer screen. For this, we choose the 100kΩ resistor that gave us a sufficient characteristics and designed a compact circuit.

[[image:Final_design.jpeg|400px|center]]

Using the photodiode, we can determine that the Red LED was flickering at 1kHz, while the refresh rate of the computer screen was approximately 50kHz.
[[image:Flicker sources.png|400px|center]]

==[[Lab Log]]==

==References==
[1] NVC Lighting UK, Technical Support - What is Flicker in Relation to Lighting? https://www.nvcuk.com/technical-support/view/what-is-flicker-in-relation-to-lighting-2

[2] A. Wilkins, J. Veitch & B. Lehman. “LED lighting flicker and potential health concerns: IEEE standard PAR1789 update, “Energy Conversion Congress and Exposition, Atlanta Georgia, pp. 171-178, 2010

Optical Sensor for Noise Flickering

2024-04-17T03:57:05Z

Amanda: /* Varying External Resistance */

==Group Members==
Eric Cheung Jun Hao; Lee An Min, Amanda; Loh Jia Ying Whitney

==Introduction and Background==
Flicker is the repeated and frequent variation in the output of light source over time. All light sources flicker but vary depending on several variables [1].

There are 4 features that have serious impact on the viewer [1]:

(1) Frequency

(2) Amplitude

(3) Wave form

(4) Light Intensity

The flicker effects can have adverse effects that impacts users as summarised by Wilkins in Table 1 [2]. As such, it is important to be able to detect frequencies when LED or sources of light fall within this range that can severely affect human functions, especially with the technological developments and the use of such technology.

''Table 1: Flicker and its Biological Effects [2]''

[[image:Flicker_Bio_effect.jpeg]]

==Objective==

The objective of this project is to characterise a given photodiode and to successfully determine the frequency of an unknown flickering light source.

[[image:Optical_sensor_circuit.jpeg | 300px | none | left ]]
''Figure 1: Potential Divider Circuit''

With a simple potential divider, consisting a resistor and a photodiode in series, the resistance and hence sensitivity of the photodiode can be determined. The photodiode resistance is a function of light exposure, more specifically it is inversely proportional to light intensity. By exposing the photodiode to visual noise tags, such as the flickering of LEDs, the resistance across the photodiode is expected to decrease and hence, a larger potential can be measured across the resistor. The output can be observed on an oscilloscope to determine the performance of the photodiode.

==Set-Up==
===Equipment Needed===

''Table 2: List of Equipment Needed''
{| class="wikitable" style="margin:auto" |
! S/N !! Item !! Description/Model No.
|-
| 1 || Soldering Iron || -
|-
| 2 || Soldering Tin || -
|-
| 3 || Wires || -
|-
| 4 || Resistors || 10k, 100k, 1M
|-
| 5 || Photodiode || Hamamatsu S5972
|-
| 6 || DC Power Supply || Matrix MPS-3005L-3
|-
| 7 || Signal Generator || Agilent 33220A
|-
| 8 || 2GHz Digital Oscilloscope || LeCroy WaveRunner 203MXi-A
|}

''Table 3: Colour, Wavelength, and Size of LEDs Used''
{| class="wikitable" style="margin:auto" |
! LED S/N !! Colour !! Wavelength (nm) !! Size (mm)
|-
| 1 || Red || 643 || 5
|-
| 2 || Amber || 605 || 5
|-
| 3 || Green || 570 || 5
|-
| 4 || Blue || 450-495 || 5
|}

===Experimental Set-up===
Characterization of the photodiode is done with three 5 mm LEDs: (i) red, 643nm; (ii) green, 570nm; and (iii) blue, 450nm to 495nm. It can be noted that the photodiode sensitivity increases with increasing wavelength of LED used.

The photodiode used in this experiment is Hamamatsu S5972 Si PIN photodiode. According to the datasheet, it has a spectral response range between 320nm to 1000nm, with a peak sensitivity at 800nm, near-infrared radiation. The cutoff frequency is 0.5GHz at a reverse bias of 10V. The terminal capacitance at a reverse bias of 2V is close to 3pF.

[[image: Optical_sensor_complete_setup.jpeg|500px]][[image: Optical_sensor_setup_closeup.jpeg|500px]]

''Figure 2: Experimental set-up (a) wide view, and (b) close-up view''

A signal generator is used to pulse the LEDs to create a flickering light source. A square wave with a peak-to-peak voltage of 2V is used across all the measurements taken. A DC power supply is used to supply 3V across the photodiode.

The performance of the photodiode will be determined by varying the following parameters: (i) wavelength of LED; (ii) external resistor in circuit; and (iii) frequency of LED blinking (1Hz - 100kHz).

The dependent variable that will be measured is the voltage reading across the external resistor.

This will allow us to determine the response of the photodiode and its efficiency (rise time) of photodiode at different wavelengths.

==Timeline and Milestone==

''Table 4: Timeline and Goals to Achieve''
{| class="wikitable" style="margin:auto"
! Week !! Dates !! Tasks
|-
| Week 7 || 4 - 8 Mar || Collecting equipment and prelimary set-up
|-
| Week 8 || 11 - 15 Mar || Complete circuit set-up and prelimary measurements
|-
| Week 9 || 18 - 22 Mar || Data collection (vary LEDs)
|-
| Week 10 || 25 - 29 Mar [Well-being day (28 Mar), Good Friday (29 Mar)]|| Data collection (vary resistance)
|-
| Week 11 || 1 - 5 Apr || Data Analysis and further measurements (if needed)
|-
| Week 12 || 8 - 12 Apr [Hari Raya (10 Apr)] || Data Analysis and explore other light sources (phone/computer screens)
|-
| Week 13 || 15 - 19 Apr || Analyse experimental results and complete documentation
|}

==Results==

===Varying External Resistance===

'''Relationship between resistance and cut-off frequency'''

It can be concluded that as external resistance increases, the cutoff frequency decreases. Decreasing the external resistance by one order of magnitude will increase the cut-off frequency by an order of magnitude. Hence, lower resistance needs to be used in order to measure at higher frequencies.

Comparing the results for red LED,

''Table 5: Cutoff Frequency of Red LED for Different Resistance Values''
{| class="wikitable" style="margin:auto"
! Resistance (Ω) !! Cutoff Frequency (kHz)!! Reasoning
|-
| 10k || 100 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=10kHz but not at 100kHz. Based on a rise time of approximately 0.01ms, the cutoff frequency can be estimated to be close to 100kHz.
|-
| 100k || 33 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=10kHz but not at 100kHz. Based on a rise time of approximately 0.03ms, the cutoff frequency can be estimated to be close to 30kHz.
|-
| 1M || 6 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=1kHz but not at 10kHz. Based on a rise time of approximately 0.15ms, the cutoff frequency can be estimated to be close to 7kHz.
|}

[[image: Optical_sensor_red.png|1000px|centre]]
''Figure 3: Signal Obtained for Red LED with Different Resistance Values''

Repeating the same analysis for the blue LED,

''Table 6: Cutoff Frequency of Blue LED for Different Resistance Values''
{| class="wikitable" style="margin:auto"
! Resistance (Ω) !! Cutoff Frequency (kHz)!! Reasoning
|-
| 10k || 500 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=10kHz but not at 100kHz. Based on a rise time of approximately 0.003ms, the cutoff frequency can be estimated to be ~300kHz.
|-
| 100k || 14 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=10kHz but not at 100kHz. Based on a rise time of approximately 0.04ms, the cutoff frequency can be estimated to be ~25kHz.
|-
| 1M || 6 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=1kHz but not at 10kHz. Based on a rise time of approximately 0.20ms, the cutoff frequency can be estimated to be close to 5kHz.
|}

[[image: Optical_sensor_blue.png|1000px|centre]]
''Figure 4: Signal Obtained for Blue LED with Different Resistance Values''

Narrowing down to the specific frequency of 1kHz for blue LED for a clearer illustration, it can be shown that with decreasing external resistance, time constant decreases which replicates the signal sent into the LED (square wave). However, a lower resistance will entail lower signal-to-noise ratio. At the lower resistance of 10kΩ, the signal captured resembles a square wave while the higher resistance of 1MΩ shows, there is an evident decay in the rise and fall of the captured signal. Furthermore, the graphs also illustrate that the background noise is more prominent at lower resistance as the steady-state value across the lower resistance is smaller.

[[image: compare_resistance_blue_1kHz.png|400px|centre]]
''Figure 5: Comparison of Signal Obtained for Blue LED at Fixed Frequency of 1kHz for Different Resistance Values''

For completeness of our discussion, the plots obtained from the measurements of the green LED is shown below. However, due to the low steady-state value of the voltage across the resistor, the rise time of the photodiode cannot be clearly determined.

[[image: Optical_sensor_green.png|1000px|centre]]
''Figure 6: Signal Obtained for Green LED with Different Resistance Values''

===Varying Wavelength===

From our experimental results, the photodiode has a faster response at longer wavelengths.
{| class="wikitable" style="margin:auto"
! LED!! Wavelength (nm) !! Resistance (Ω) !! Rise Time (ms) !! Remarks
|-
| Red || 643 ||10k || 0.01 ||
|-
| || || 100k || 0.03 ||
|-
| || || 1M || 0.16 ||
|-
| Green || 570 || 10k, 100k, 1M || N.A. || Low signal-to-noise ratio
|-
| Blue|| 450-495 || 10k || 0.002 ||
|-
| || || 100k || 0.07 ||
|-
| || || 1M || 0.18
|}

Out of the three LEDs used, the signal-to-noise ratio of the green LED is the lowest. Powering the three LEDs reveals that with the same voltage supplied, the green LED is the dimmest. Thus, the intensity of incident green light on the photodiode is significantly lower. The signal captured by the photodiode is lower and hence, the decrease in resistance of the photodiode is smaller. As a result, the voltage across the external resistor in the circuit of a fixed resistance is lower. Because of this, the change in voltage reading (in the switching of the LED) on the oscilloscope is closer to background noise. Thus, signal-to-noise ratio is lower.

[[image: LED_brightness.jpeg|300px|centre]]

Considering LEDs flickering at 100Hz, the following steady-state values for voltage across the external resistor were obtained.

For the Red LED,
{| class="wikitable" style="margin:auto"
! Resistance (Ω)!! Steady State Value (V)
|-
| 10k || 0.03
|-
| 100k || 0.40
|-
| 1M|| 2.16
|}

For the Blue LED,
{| class="wikitable" style="margin:auto"
! Resistance (Ω)!! Steady State Value (V)
|-
| 10k || 0.05
|-
| 100k || 0.47
|-
| 1M|| 2.44
|}

The steady-state value is dependent on the photosensitivity at different wavelengths and the brightness of the LED.

===Other Light Source(s)===
The photodiode is used to characterise the flickering of a computer screen. For this, we choose the 100kΩ resistor that gave us a sufficient characteristics and designed a compact circuit.

[[image:Final_design.jpeg|400px|center]]

Using the photodiode, we can determine that the Red LED was flickering at 1kHz, while the refresh rate of the computer screen was approximately 50kHz.
[[image:Flicker sources.png|400px|center]]

==[[Lab Log]]==

==References==
[1] NVC Lighting UK, Technical Support - What is Flicker in Relation to Lighting? https://www.nvcuk.com/technical-support/view/what-is-flicker-in-relation-to-lighting-2

[2] A. Wilkins, J. Veitch & B. Lehman. “LED lighting flicker and potential health concerns: IEEE standard PAR1789 update, “Energy Conversion Congress and Exposition, Atlanta Georgia, pp. 171-178, 2010

Optical Sensor for Noise Flickering

2024-04-17T03:55:53Z

Amanda: /* Varying External Resistance */

==Group Members==
Eric Cheung Jun Hao; Lee An Min, Amanda; Loh Jia Ying Whitney

==Introduction and Background==
Flicker is the repeated and frequent variation in the output of light source over time. All light sources flicker but vary depending on several variables [1].

There are 4 features that have serious impact on the viewer [1]:

(1) Frequency

(2) Amplitude

(3) Wave form

(4) Light Intensity

The flicker effects can have adverse effects that impacts users as summarised by Wilkins in Table 1 [2]. As such, it is important to be able to detect frequencies when LED or sources of light fall within this range that can severely affect human functions, especially with the development of technology and use of such technology.

''Table 1: Flicker and its Biological Effects [2]''

[[image:Flicker_Bio_effect.jpeg]]

==Objective==

The objective of this project is to characterise a given photodiode and to successfully determine the frequency of an unknown flickering light source.

[[image:Optical_sensor_circuit.jpeg | 300px | none | left ]]
''Figure 1: Potential Divider Circuit''

With a simple potential divider, consisting a resistor and a photodiode in series, the resistance and hence sensitivity of the photodiode can be determined. The photodiode resistance is a function of light exposure, more specifically it is inversely proportional to light intensity. By exposing the photodiode to visual noise tags, such as the flickering of LEDs, the resistance across the photodiode is expected to decrease and hence, a larger potential can be measured across the resistor. The output can be observed on an oscilloscope to determine the performance of the photodiode.

==Set-Up==
===Equipment Needed===

''Table 2: List of Equipment Needed''
{| class="wikitable" style="margin:auto" |
! S/N !! Item !! Description/Model No.
|-
| 1 || Soldering Iron || -
|-
| 2 || Soldering Tin || -
|-
| 3 || Wires || -
|-
| 4 || Resistors || 10k, 100k, 1M
|-
| 5 || Photodiode || Hamamatsu S5972
|-
| 6 || DC Power Supply || Matrix MPS-3005L-3
|-
| 7 || Signal Generator || Agilent 33220A
|-
| 8 || 2GHz Digital Oscilloscope || LeCroy WaveRunner 203MXi-A
|}

''Table 3: Colour, Wavelength, and Size of LEDs Used''
{| class="wikitable" style="margin:auto" |
! LED S/N !! Colour !! Wavelength (nm) !! Size (mm)
|-
| 1 || Red || 643 || 5
|-
| 2 || Amber || 605 || 5
|-
| 3 || Green || 570 || 5
|-
| 4 || Blue || 450-495 || 5
|}

===Experimental Set-up===
Characterization of the photodiode is done with three 5 mm LEDs: (i) red, 643nm; (ii) green, 570nm; and (iii) blue, 450nm to 495nm. It can be noted that the photodiode sensitivity increases with increasing wavelength of LED used.

The photodiode used in this experiment is Hamamatsu S5972 Si PIN photodiode. According to the datasheet, it has a spectral response range between 320nm to 1000nm, with a peak sensitivity at 800nm, near-infrared radiation. The cutoff frequency is 0.5GHz at a reverse bias of 10V. The terminal capacitance at a reverse bias of 2V is close to 3pF.

[[image: Optical_sensor_complete_setup.jpeg|500px]][[image: Optical_sensor_setup_closeup.jpeg|500px]]

''Figure 2: Experimental set-up (a) wide view, and (b) close-up view''

A signal generator is used to pulse the LEDs to create a flickering light source. A square wave with a peak-to-peak voltage of 2V is used across all the measurements taken. A DC power supply is used to supply 3V across the photodiode.

The performance of the photodiode will be determined by varying the following parameters: (i) wavelength of LED; (ii) external resistor in circuit; and (iii) frequency of LED blinking (1Hz - 100kHz).

The dependent variable that will be measured is the voltage reading across the external resistor.

This will allow us to determine the response of the photodiode and its efficiency (rise time) of photodiode at different wavelengths.

==Timeline and Milestone==

''Table 4: Timeline and Goals to Achieve''
{| class="wikitable" style="margin:auto"
! Week !! Dates !! Tasks
|-
| Week 7 || 4 - 8 Mar || Collecting equipment and prelimary set-up
|-
| Week 8 || 11 - 15 Mar || Complete circuit set-up and prelimary measurements
|-
| Week 9 || 18 - 22 Mar || Data collection (vary LEDs)
|-
| Week 10 || 25 - 29 Mar [Well-being day (28 Mar), Good Friday (29 Mar)]|| Data collection (vary resistance)
|-
| Week 11 || 1 - 5 Apr || Data Analysis and further measurements (if needed)
|-
| Week 12 || 8 - 12 Apr [Hari Raya (10 Apr)] || Data Analysis and explore other light sources (phone/computer screens)
|-
| Week 13 || 15 - 19 Apr || Analyse experimental results and complete documentation
|}

==Results==

===Varying External Resistance===

'''Relationship between resistance and cut-off frequency'''

It can be concluded that as external resistance increases, the cutoff frequency decreases. Decreasing the external resistance by one order of magnitude will increase the cut-off frequency by an order of magnitude. Hence, lower resistance needs to be used in order to measure at higher frequencies.

Comparing the results for red LED,

''Table 5: Cutoff Frequency of Red LED for Different Resistance Values''
{| class="wikitable" style="margin:auto"
! Resistance (Ω) !! Cutoff Frequency (kHz)!! Reasoning
|-
| 10k || 100 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=10kHz but not at 100kHz. Based on a rise time of approximately 0.01ms, the cutoff frequency can be estimated to be close to 100kHz.
|-
| 100k || 33 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=10kHz but not at 100kHz. Based on a rise time of approximately 0.03ms, the cutoff frequency can be estimated to be close to 30kHz.
|-
| 1M || 6 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=1kHz but not at 10kHz. Based on a rise time of approximately 0.15ms, the cutoff frequency can be estimated to be close to 7kHz.
|}

[[image: Optical_sensor_red.png|1000px|centre]]
''Figure 3: Signal Obtained for Red LED with Different Resistance Values''

Repeating the same analysis for the blue LED,

''Table 6: Cutoff Frequency of Blue LED for Different Resistance Values''
{| class="wikitable" style="margin:auto"
! Resistance (Ω) !! Cutoff Frequency (kHz)!! Reasoning
|-
| 10k || 500 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=10kHz but not at 100kHz. Based on a rise time of approximately 0.003ms, the cutoff frequency can be estimated to be ~300kHz.
|-
| 100k || 14 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=10kHz but not at 100kHz. Based on a rise time of approximately 0.04ms, the cutoff frequency can be estimated to be ~25kHz.
|-
| 1M || 6 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=1kHz but not at 10kHz. Based on a rise time of approximately 0.20ms, the cutoff frequency can be estimated to be close to 5kHz.
|}

[[image: Optical_sensor_blue.png|1000px|centre]]
''Figure 4: Signal Obtained for Red LED with Different Resistance Values''

Narrowing down to the specific frequency of 1kHz for blue LED for a clearer illustration, it can be shown that with decreasing external resistance, time constant decreases which replicates the signal sent into the LED (square wave). However, a lower resistance will entail lower signal-to-noise ratio. At the lower resistance of 10kΩ, the signal captured resembles a square wave while the higher resistance of 1MΩ shows, there is an evident decay in the rise and fall of the captured signal. Furthermore, the graphs also illustrate that the background noise is more prominent at lower resistance as the steady-state value across the lower resistance is smaller.

[[image: compare_resistance_blue_1kHz.png|400px|centre]]
''Figure 5: Signal Obtained for Red LED with Different Resistance Values''

For completeness of our discussion, the plots obtained from the measurements of the green LED is shown below. However, due to the low steady-state value of the voltage across the resistor, the rise time of the photodiode cannot be clearly determined.

[[image: Optical_sensor_green.png|1000px|centre]]

===Varying Wavelength===

From our experimental results, the photodiode has a faster response at longer wavelengths.
{| class="wikitable" style="margin:auto"
! LED!! Wavelength (nm) !! Resistance (Ω) !! Rise Time (ms) !! Remarks
|-
| Red || 643 ||10k || 0.01 ||
|-
| || || 100k || 0.03 ||
|-
| || || 1M || 0.16 ||
|-
| Green || 570 || 10k, 100k, 1M || N.A. || Low signal-to-noise ratio
|-
| Blue|| 450-495 || 10k || 0.002 ||
|-
| || || 100k || 0.07 ||
|-
| || || 1M || 0.18
|}

Out of the three LEDs used, the signal-to-noise ratio of the green LED is the lowest. Powering the three LEDs reveals that with the same voltage supplied, the green LED is the dimmest. Thus, the intensity of incident green light on the photodiode is significantly lower. The signal captured by the photodiode is lower and hence, the decrease in resistance of the photodiode is smaller. As a result, the voltage across the external resistor in the circuit of a fixed resistance is lower. Because of this, the change in voltage reading (in the switching of the LED) on the oscilloscope is closer to background noise. Thus, signal-to-noise ratio is lower.

[[image: LED_brightness.jpeg|300px|centre]]

Considering LEDs flickering at 100Hz, the following steady-state values for voltage across the external resistor were obtained.

For the Red LED,
{| class="wikitable" style="margin:auto"
! Resistance (Ω)!! Steady State Value (V)
|-
| 10k || 0.03
|-
| 100k || 0.40
|-
| 1M|| 2.16
|}

For the Blue LED,
{| class="wikitable" style="margin:auto"
! Resistance (Ω)!! Steady State Value (V)
|-
| 10k || 0.05
|-
| 100k || 0.47
|-
| 1M|| 2.44
|}

The steady-state value is dependent on the photosensitivity at different wavelengths and the brightness of the LED.

===Other Light Source(s)===
The photodiode is used to characterise the flickering of a computer screen. For this, we choose the 100kΩ resistor that gave us a sufficient characteristics and designed a compact circuit.

[[image:Final_design.jpeg|400px|center]]

Using the photodiode, we can determine that the Red LED was flickering at 1kHz, while the refresh rate of the computer screen was approximately 50kHz.
[[image:Flicker sources.png|400px|center]]

==[[Lab Log]]==

==References==
[1] NVC Lighting UK, Technical Support - What is Flicker in Relation to Lighting? https://www.nvcuk.com/technical-support/view/what-is-flicker-in-relation-to-lighting-2

[2] A. Wilkins, J. Veitch & B. Lehman. “LED lighting flicker and potential health concerns: IEEE standard PAR1789 update, “Energy Conversion Congress and Exposition, Atlanta Georgia, pp. 171-178, 2010

Optical Sensor for Noise Flickering

2024-04-17T03:55:20Z

Amanda: /* Varying External Resistance */

==Group Members==
Eric Cheung Jun Hao; Lee An Min, Amanda; Loh Jia Ying Whitney

==Introduction and Background==
Flicker is the repeated and frequent variation in the output of light source over time. All light sources flicker but vary depending on several variables [1].

There are 4 features that have serious impact on the viewer [1]:

(1) Frequency

(2) Amplitude

(3) Wave form

(4) Light Intensity

The flicker effects can have adverse effects that impacts users as summarised by Wilkins in Table 1 [2]. As such, it is important to be able to detect frequencies when LED or sources of light fall within this range that can severely affect human functions, especially with the development of technology and use of such technology.

''Table 1: Flicker and its Biological Effects [2]''

[[image:Flicker_Bio_effect.jpeg]]

==Objective==

The objective of this project is to characterise a given photodiode and to successfully determine the frequency of an unknown flickering light source.

[[image:Optical_sensor_circuit.jpeg | 300px | none | left ]]
''Figure 1: Potential Divider Circuit''

With a simple potential divider, consisting a resistor and a photodiode in series, the resistance and hence sensitivity of the photodiode can be determined. The photodiode resistance is a function of light exposure, more specifically it is inversely proportional to light intensity. By exposing the photodiode to visual noise tags, such as the flickering of LEDs, the resistance across the photodiode is expected to decrease and hence, a larger potential can be measured across the resistor. The output can be observed on an oscilloscope to determine the performance of the photodiode.

==Set-Up==
===Equipment Needed===

''Table 2: List of Equipment Needed''
{| class="wikitable" style="margin:auto" |
! S/N !! Item !! Description/Model No.
|-
| 1 || Soldering Iron || -
|-
| 2 || Soldering Tin || -
|-
| 3 || Wires || -
|-
| 4 || Resistors || 10k, 100k, 1M
|-
| 5 || Photodiode || Hamamatsu S5972
|-
| 6 || DC Power Supply || Matrix MPS-3005L-3
|-
| 7 || Signal Generator || Agilent 33220A
|-
| 8 || 2GHz Digital Oscilloscope || LeCroy WaveRunner 203MXi-A
|}

''Table 3: Colour, Wavelength, and Size of LEDs Used''
{| class="wikitable" style="margin:auto" |
! LED S/N !! Colour !! Wavelength (nm) !! Size (mm)
|-
| 1 || Red || 643 || 5
|-
| 2 || Amber || 605 || 5
|-
| 3 || Green || 570 || 5
|-
| 4 || Blue || 450-495 || 5
|}

===Experimental Set-up===
Characterization of the photodiode is done with three 5 mm LEDs: (i) red, 643nm; (ii) green, 570nm; and (iii) blue, 450nm to 495nm. It can be noted that the photodiode sensitivity increases with increasing wavelength of LED used.

The photodiode used in this experiment is Hamamatsu S5972 Si PIN photodiode. According to the datasheet, it has a spectral response range between 320nm to 1000nm, with a peak sensitivity at 800nm, near-infrared radiation. The cutoff frequency is 0.5GHz at a reverse bias of 10V. The terminal capacitance at a reverse bias of 2V is close to 3pF.

[[image: Optical_sensor_complete_setup.jpeg|500px]][[image: Optical_sensor_setup_closeup.jpeg|500px]]

''Figure 2: Experimental set-up (a) wide view, and (b) close-up view''

A signal generator is used to pulse the LEDs to create a flickering light source. A square wave with a peak-to-peak voltage of 2V is used across all the measurements taken. A DC power supply is used to supply 3V across the photodiode.

The performance of the photodiode will be determined by varying the following parameters: (i) wavelength of LED; (ii) external resistor in circuit; and (iii) frequency of LED blinking (1Hz - 100kHz).

The dependent variable that will be measured is the voltage reading across the external resistor.

This will allow us to determine the response of the photodiode and its efficiency (rise time) of photodiode at different wavelengths.

==Timeline and Milestone==

''Table 4: Timeline and Goals to Achieve''
{| class="wikitable" style="margin:auto"
! Week !! Dates !! Tasks
|-
| Week 7 || 4 - 8 Mar || Collecting equipment and prelimary set-up
|-
| Week 8 || 11 - 15 Mar || Complete circuit set-up and prelimary measurements
|-
| Week 9 || 18 - 22 Mar || Data collection (vary LEDs)
|-
| Week 10 || 25 - 29 Mar [Well-being day (28 Mar), Good Friday (29 Mar)]|| Data collection (vary resistance)
|-
| Week 11 || 1 - 5 Apr || Data Analysis and further measurements (if needed)
|-
| Week 12 || 8 - 12 Apr [Hari Raya (10 Apr)] || Data Analysis and explore other light sources (phone/computer screens)
|-
| Week 13 || 15 - 19 Apr || Analyse experimental results and complete documentation
|}

==Results==

===Varying External Resistance===

'''Relationship between resistance and cut-off frequency'''

It can be concluded that as external resistance increases, the cutoff frequency decreases. Decreasing the external resistance by one order of magnitude will increase the cut-off frequency by an order of magnitude. Hence, lower resistance needs to be used in order to measure at higher frequencies.

Comparing the results for red LED,

''Table 5: Cutoff Frequency of Red LED for Different Resistance Values''
{| class="wikitable" style="margin:auto"
! Resistance (Ω) !! Cutoff Frequency (kHz)!! Reasoning
|-
| 10k || 100 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=10kHz but not at 100kHz. Based on a rise time of approximately 0.01ms, the cutoff frequency can be estimated to be close to 100kHz.
|-
| 100k || 33 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=10kHz but not at 100kHz. Based on a rise time of approximately 0.03ms, the cutoff frequency can be estimated to be close to 30kHz.
|-
| 1M || 6 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=1kHz but not at 10kHz. Based on a rise time of approximately 0.15ms, the cutoff frequency can be estimated to be close to 7kHz.
|}

[[image: Optical_sensor_red.png|1000px|centre]]
''Figure 3: Signal Obtained for Red LED with Different Resistance Values''

Repeating the same analysis for the blue LED,

''Table 6: Cutoff Frequency of Blue LED for Different Resistance Values''
{| class="wikitable" style="margin:auto"
! Resistance (Ω) !! Cutoff Frequency (kHz)!! Reasoning
|-
| 10k || 500 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=10kHz but not at 100kHz. Based on a rise time of approximately 0.003ms, the cutoff frequency can be estimated to be ~300kHz.
|-
| 100k || 14 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=10kHz but not at 100kHz. Based on a rise time of approximately 0.04ms, the cutoff frequency can be estimated to be ~25kHz.
|-
| 1M || 6 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=1kHz but not at 10kHz. Based on a rise time of approximately 0.20ms, the cutoff frequency can be estimated to be close to 5kHz.
|}

[[image: Optical_sensor_blue.png|1000px|centre]]
''Figure 4: Signal Obtained for Red LED with Different Resistance Values''

Narrowing down to the specific frequency of 1kHz for blue LED for a clearer illustration, it can be shown that with decreasing external resistance, time constant decreases which replicates the signal sent into the LED (square wave). However, a lower resistance will entail lower signal-to-noise ratio. At the lower resistance of 10kΩ, the signal captured resembles a square wave while the higher resistance of 1MΩ shows, there is an evident decay in the rise and fall of the captured signal. Furthermore, the graphs also illustrate that the background noise is more prominent at lower resistance as the steady-state value across the lower resistance is smaller.

[[image: compare_resistance_blue_1kHz.png|400px|centre]]

For completeness of our discussion, the plots obtained from the measurements of the green LED is shown below. However, due to the low steady-state value of the voltage across the resistor, the rise time of the photodiode cannot be clearly determined.

[[image: Optical_sensor_green.png|1000px|centre]]

===Varying Wavelength===

From our experimental results, the photodiode has a faster response at longer wavelengths.
{| class="wikitable" style="margin:auto"
! LED!! Wavelength (nm) !! Resistance (Ω) !! Rise Time (ms) !! Remarks
|-
| Red || 643 ||10k || 0.01 ||
|-
| || || 100k || 0.03 ||
|-
| || || 1M || 0.16 ||
|-
| Green || 570 || 10k, 100k, 1M || N.A. || Low signal-to-noise ratio
|-
| Blue|| 450-495 || 10k || 0.002 ||
|-
| || || 100k || 0.07 ||
|-
| || || 1M || 0.18
|}

Out of the three LEDs used, the signal-to-noise ratio of the green LED is the lowest. Powering the three LEDs reveals that with the same voltage supplied, the green LED is the dimmest. Thus, the intensity of incident green light on the photodiode is significantly lower. The signal captured by the photodiode is lower and hence, the decrease in resistance of the photodiode is smaller. As a result, the voltage across the external resistor in the circuit of a fixed resistance is lower. Because of this, the change in voltage reading (in the switching of the LED) on the oscilloscope is closer to background noise. Thus, signal-to-noise ratio is lower.

[[image: LED_brightness.jpeg|300px|centre]]

Considering LEDs flickering at 100Hz, the following steady-state values for voltage across the external resistor were obtained.

For the Red LED,
{| class="wikitable" style="margin:auto"
! Resistance (Ω)!! Steady State Value (V)
|-
| 10k || 0.03
|-
| 100k || 0.40
|-
| 1M|| 2.16
|}

For the Blue LED,
{| class="wikitable" style="margin:auto"
! Resistance (Ω)!! Steady State Value (V)
|-
| 10k || 0.05
|-
| 100k || 0.47
|-
| 1M|| 2.44
|}

The steady-state value is dependent on the photosensitivity at different wavelengths and the brightness of the LED.

===Other Light Source(s)===
The photodiode is used to characterise the flickering of a computer screen. For this, we choose the 100kΩ resistor that gave us a sufficient characteristics and designed a compact circuit.

[[image:Final_design.jpeg|400px|center]]

Using the photodiode, we can determine that the Red LED was flickering at 1kHz, while the refresh rate of the computer screen was approximately 50kHz.
[[image:Flicker sources.png|400px|center]]

==[[Lab Log]]==

==References==
[1] NVC Lighting UK, Technical Support - What is Flicker in Relation to Lighting? https://www.nvcuk.com/technical-support/view/what-is-flicker-in-relation-to-lighting-2

[2] A. Wilkins, J. Veitch & B. Lehman. “LED lighting flicker and potential health concerns: IEEE standard PAR1789 update, “Energy Conversion Congress and Exposition, Atlanta Georgia, pp. 171-178, 2010

Optical Sensor for Noise Flickering

2024-04-17T03:53:58Z

Amanda: /* Varying External Resistance */

==Group Members==
Eric Cheung Jun Hao; Lee An Min, Amanda; Loh Jia Ying Whitney

==Introduction and Background==
Flicker is the repeated and frequent variation in the output of light source over time. All light sources flicker but vary depending on several variables [1].

There are 4 features that have serious impact on the viewer [1]:

(1) Frequency

(2) Amplitude

(3) Wave form

(4) Light Intensity

The flicker effects can have adverse effects that impacts users as summarised by Wilkins in Table 1 [2]. As such, it is important to be able to detect frequencies when LED or sources of light fall within this range that can severely affect human functions, especially with the development of technology and use of such technology.

''Table 1: Flicker and its Biological Effects [2]''

[[image:Flicker_Bio_effect.jpeg]]

==Objective==

The objective of this project is to characterise a given photodiode and to successfully determine the frequency of an unknown flickering light source.

[[image:Optical_sensor_circuit.jpeg | 300px | none | left ]]
''Figure 1: Potential Divider Circuit''

With a simple potential divider, consisting a resistor and a photodiode in series, the resistance and hence sensitivity of the photodiode can be determined. The photodiode resistance is a function of light exposure, more specifically it is inversely proportional to light intensity. By exposing the photodiode to visual noise tags, such as the flickering of LEDs, the resistance across the photodiode is expected to decrease and hence, a larger potential can be measured across the resistor. The output can be observed on an oscilloscope to determine the performance of the photodiode.

==Set-Up==
===Equipment Needed===

''Table 2: List of Equipment Needed''
{| class="wikitable" style="margin:auto" |
! S/N !! Item !! Description/Model No.
|-
| 1 || Soldering Iron || -
|-
| 2 || Soldering Tin || -
|-
| 3 || Wires || -
|-
| 4 || Resistors || 10k, 100k, 1M
|-
| 5 || Photodiode || Hamamatsu S5972
|-
| 6 || DC Power Supply || Matrix MPS-3005L-3
|-
| 7 || Signal Generator || Agilent 33220A
|-
| 8 || 2GHz Digital Oscilloscope || LeCroy WaveRunner 203MXi-A
|}

''Table 3: Colour, Wavelength, and Size of LEDs Used''
{| class="wikitable" style="margin:auto" |
! LED S/N !! Colour !! Wavelength (nm) !! Size (mm)
|-
| 1 || Red || 643 || 5
|-
| 2 || Amber || 605 || 5
|-
| 3 || Green || 570 || 5
|-
| 4 || Blue || 450-495 || 5
|}

===Experimental Set-up===
Characterization of the photodiode is done with three 5 mm LEDs: (i) red, 643nm; (ii) green, 570nm; and (iii) blue, 450nm to 495nm. It can be noted that the photodiode sensitivity increases with increasing wavelength of LED used.

The photodiode used in this experiment is Hamamatsu S5972 Si PIN photodiode. According to the datasheet, it has a spectral response range between 320nm to 1000nm, with a peak sensitivity at 800nm, near infrared radiation. The cutoff frequency is 0.5GHz at reverse bias of 10V. The terminal capacitance at a reverse bias of 2V is close to 3pF.

[[image: Optical_sensor_complete_setup.jpeg|500px]][[image: Optical_sensor_setup_closeup.jpeg|500px]]

''Figure 2: Experimental set-up (a) wide view, and (b) close-up view''

A signal generator is used to pulse the LEDs to create a flickering light source. A square wave with a peak-to-peak voltage of 2V is used across all the measurements taken. A DC power supply is used to supply 3V across the photodiode.

The performance of the photodiode will be determined by varying the following parameters: (i) wavelength of LED; (ii) external resistor in circuit; and (iii) frequency of LED blinking (1Hz - 100kHz).

The dependent variable that will be measured is the voltage reading across external resistor.

This will allow us to determine the response of photodiode and efficiency (Time decay) of photodiode at different wavelengths.

==Timeline and Milestone==

''Table 4: Timeline and Goals to Achieve''
{| class="wikitable" style="margin:auto"
! Week !! Dates !! Tasks
|-
| Week 7 || 4 - 8 Mar || Collecting equipment and prelimary set-up
|-
| Week 8 || 11 - 15 Mar || Complete circuit set-up and prelimary measurements
|-
| Week 9 || 18 - 22 Mar || Data collection (vary LEDs)
|-
| Week 10 || 25 - 29 Mar [Well-being day (28 Mar), Good Friday (29 Mar)]|| Data collection (vary resistance)
|-
| Week 11 || 1 - 5 Apr || Data Analysis and further measurements (if needed)
|-
| Week 12 || 8 - 12 Apr [Hari Raya (10 Apr)] || Data Analysis and explore other light sources (phone/computer screens)
|-
| Week 13 || 15 - 19 Apr || Analyse experimental results and complete documentation
|}

==Results==

===Varying External Resistance===

'''Relationship between resistance and cut-off frequency'''

It can be concluded that as external resistance increases, the cutoff frequency decreases. Decreasing the external resistance by one order of magnitude will increase the cut-off frequency by an order of magnitude. Hence, lower resistance needs to be used in order to measure at higher frequencies.

Comparing the results for red LED,

''Table 5: Cutoff Frequency of Red LED for Different Resistance Values''
{| class="wikitable" style="margin:auto"
! Resistance (Ω) !! Cutoff Frequency (kHz)!! Reasoning
|-
| 10k || 100 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=10kHz but not at 100kHz. Based on a rise time of approximately 0.01ms, the cutoff frequency can be estimated to be close to 100kHz.
|-
| 100k || 33 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=10kHz but not at 100kHz. Based on a rise time of approximately 0.03ms, the cutoff frequency can be estimated to be close to 30kHz.
|-
| 1M || 6 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=1kHz but not at 10kHz. Based on a rise time of approximately 0.15ms, the cutoff frequency can be estimated to be close to 7kHz.
|}

[[image: Optical_sensor_red.png|1000px|centre]]

Repeating the same analysis for the blue LED,

{| class="wikitable" style="margin:auto"
! Resistance (Ω) !! Cutoff Frequency (kHz)!! Reasoning
|-
| 10k || 500 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=10kHz but not at 100kHz. Based on a rise time of approximately 0.003ms, the cutoff frequency can be estimated to be ~300kHz.
|-
| 100k || 14 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=10kHz but not at 100kHz. Based on a rise time of approximately 0.04ms, the cutoff frequency can be estimated to be ~25kHz.
|-
| 1M || 6 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=1kHz but not at 10kHz. Based on a rise time of approximately 0.20ms, the cutoff frequency can be estimated to be close to 5kHz.
|}

[[image: Optical_sensor_blue.png|1000px|centre]]

Narrowing down to the specific frequency of 1kHz for blue LED for a clearer illustration, it can be shown that with decreasing external resistance, time constant decreases which replicates the signal sent into the LED (square wave). However, a lower resistance will entail lower signal-to-noise ratio. At the lower resistance of 10kΩ, the signal captured resembles a square wave while the higher resistance of 1MΩ shows, there is an evident decay in the rise and fall of the captured signal. Furthermore, the graphs also illustrate that the background noise is more prominent at lower resistance as the steady-state value across the lower resistance is smaller.

[[image: compare_resistance_blue_1kHz.png|400px|centre]]

For completeness of our discussion, the plots obtained from the measurements of the green LED is shown below. However, due to the low steady-state value of the voltage across the resistor, the rise time of the photodiode cannot be clearly determined.

[[image: Optical_sensor_green.png|1000px|centre]]

===Varying Wavelength===

From our experimental results, the photodiode has a faster response at longer wavelengths.
{| class="wikitable" style="margin:auto"
! LED!! Wavelength (nm) !! Resistance (Ω) !! Rise Time (ms) !! Remarks
|-
| Red || 643 ||10k || 0.01 ||
|-
| || || 100k || 0.03 ||
|-
| || || 1M || 0.16 ||
|-
| Green || 570 || 10k, 100k, 1M || N.A. || Low signal-to-noise ratio
|-
| Blue|| 450-495 || 10k || 0.002 ||
|-
| || || 100k || 0.07 ||
|-
| || || 1M || 0.18
|}

Out of the three LEDs used, the signal-to-noise ratio of the green LED is the lowest. Powering the three LEDs reveals that with the same voltage supplied, the green LED is the dimmest. Thus, the intensity of incident green light on the photodiode is significantly lower. The signal captured by the photodiode is lower and hence, the decrease in resistance of the photodiode is smaller. As a result, the voltage across the external resistor in the circuit of a fixed resistance is lower. Because of this, the change in voltage reading (in the switching of the LED) on the oscilloscope is closer to background noise. Thus, signal-to-noise ratio is lower.

[[image: LED_brightness.jpeg|300px|centre]]

Considering LEDs flickering at 100Hz, the following steady-state values for voltage across the external resistor were obtained.

For the Red LED,
{| class="wikitable" style="margin:auto"
! Resistance (Ω)!! Steady State Value (V)
|-
| 10k || 0.03
|-
| 100k || 0.40
|-
| 1M|| 2.16
|}

For the Blue LED,
{| class="wikitable" style="margin:auto"
! Resistance (Ω)!! Steady State Value (V)
|-
| 10k || 0.05
|-
| 100k || 0.47
|-
| 1M|| 2.44
|}

The steady-state value is dependent on the photosensitivity at different wavelengths and the brightness of the LED.

===Other Light Source(s)===
The photodiode is used to characterise the flickering of a computer screen. For this, we choose the 100kΩ resistor that gave us a sufficient characteristics and designed a compact circuit.

[[image:Final_design.jpeg|400px|center]]

Using the photodiode, we can determine that the Red LED was flickering at 1kHz, while the refresh rate of the computer screen was approximately 50kHz.
[[image:Flicker sources.png|400px|center]]

==[[Lab Log]]==

==References==
[1] NVC Lighting UK, Technical Support - What is Flicker in Relation to Lighting? https://www.nvcuk.com/technical-support/view/what-is-flicker-in-relation-to-lighting-2

[2] A. Wilkins, J. Veitch & B. Lehman. “LED lighting flicker and potential health concerns: IEEE standard PAR1789 update, “Energy Conversion Congress and Exposition, Atlanta Georgia, pp. 171-178, 2010

Optical Sensor for Noise Flickering

2024-04-17T03:53:07Z

Amanda: /* Timeline and Milestone */

==Group Members==
Eric Cheung Jun Hao; Lee An Min, Amanda; Loh Jia Ying Whitney

==Introduction and Background==
Flicker is the repeated and frequent variation in the output of light source over time. All light sources flicker but vary depending on several variables [1].

There are 4 features that have serious impact on the viewer [1]:

(1) Frequency

(2) Amplitude

(3) Wave form

(4) Light Intensity

The flicker effects can have adverse effects that impacts users as summarised by Wilkins in Table 1 [2]. As such, it is important to be able to detect frequencies when LED or sources of light fall within this range that can severely affect human functions, especially with the development of technology and use of such technology.

''Table 1: Flicker and its Biological Effects [2]''

[[image:Flicker_Bio_effect.jpeg]]

==Objective==

The objective of this project is to characterise a given photodiode and to successfully determine the frequency of an unknown flickering light source.

[[image:Optical_sensor_circuit.jpeg | 300px | none | left ]]
''Figure 1: Potential Divider Circuit''

With a simple potential divider, consisting a resistor and a photodiode in series, the resistance and hence sensitivity of the photodiode can be determined. The photodiode resistance is a function of light exposure, more specifically it is inversely proportional to light intensity. By exposing the photodiode to visual noise tags, such as the flickering of LEDs, the resistance across the photodiode is expected to decrease and hence, a larger potential can be measured across the resistor. The output can be observed on an oscilloscope to determine the performance of the photodiode.

==Set-Up==
===Equipment Needed===

''Table 2: List of Equipment Needed''
{| class="wikitable" style="margin:auto" |
! S/N !! Item !! Description/Model No.
|-
| 1 || Soldering Iron || -
|-
| 2 || Soldering Tin || -
|-
| 3 || Wires || -
|-
| 4 || Resistors || 10k, 100k, 1M
|-
| 5 || Photodiode || Hamamatsu S5972
|-
| 6 || DC Power Supply || Matrix MPS-3005L-3
|-
| 7 || Signal Generator || Agilent 33220A
|-
| 8 || 2GHz Digital Oscilloscope || LeCroy WaveRunner 203MXi-A
|}

''Table 3: Colour, Wavelength, and Size of LEDs Used''
{| class="wikitable" style="margin:auto" |
! LED S/N !! Colour !! Wavelength (nm) !! Size (mm)
|-
| 1 || Red || 643 || 5
|-
| 2 || Amber || 605 || 5
|-
| 3 || Green || 570 || 5
|-
| 4 || Blue || 450-495 || 5
|}

===Experimental Set-up===
Characterization of the photodiode is done with three 5 mm LEDs: (i) red, 643nm; (ii) green, 570nm; and (iii) blue, 450nm to 495nm. It can be noted that the photodiode sensitivity increases with increasing wavelength of LED used.

The photodiode used in this experiment is Hamamatsu S5972 Si PIN photodiode. According to the datasheet, it has a spectral response range between 320nm to 1000nm, with a peak sensitivity at 800nm, near infrared radiation. The cutoff frequency is 0.5GHz at reverse bias of 10V. The terminal capacitance at a reverse bias of 2V is close to 3pF.

[[image: Optical_sensor_complete_setup.jpeg|500px]][[image: Optical_sensor_setup_closeup.jpeg|500px]]

''Figure 2: Experimental set-up (a) wide view, and (b) close-up view''

A signal generator is used to pulse the LEDs to create a flickering light source. A square wave with a peak-to-peak voltage of 2V is used across all the measurements taken. A DC power supply is used to supply 3V across the photodiode.

The performance of the photodiode will be determined by varying the following parameters: (i) wavelength of LED; (ii) external resistor in circuit; and (iii) frequency of LED blinking (1Hz - 100kHz).

The dependent variable that will be measured is the voltage reading across external resistor

This will allow us to determine the response of photodiode and efficiency (Time decay) of photodiode at different wavelengths.

==Timeline and Milestone==

''Table 4: Timeline and Goals to Achieve''
{| class="wikitable" style="margin:auto"
! Week !! Dates !! Tasks
|-
| Week 7 || 4 - 8 Mar || Collecting equipment and prelimary set-up
|-
| Week 8 || 11 - 15 Mar || Complete circuit set-up and prelimary measurements
|-
| Week 9 || 18 - 22 Mar || Data collection (vary LEDs)
|-
| Week 10 || 25 - 29 Mar [Well-being day (28 Mar), Good Friday (29 Mar)]|| Data collection (vary resistance)
|-
| Week 11 || 1 - 5 Apr || Data Analysis and further measurements (if needed)
|-
| Week 12 || 8 - 12 Apr [Hari Raya (10 Apr)] || Data Analysis and explore other light sources (phone/computer screens)
|-
| Week 13 || 15 - 19 Apr || Analyse experimental results and complete documentation
|}

==Results==

===Varying External Resistance===

'''Relationship between resistance and cut-off frequency'''

It can be concluded that as external resistance increases, the cutoff frequency decreases. Decreasing the external resistance by one order of magnitude will increase the cut-off frequency by an order of magnitude. Hence, lower resistance needs to be used in order to measure at higher frequencies.

Comparing the results for red LED,

{| class="wikitable" style="margin:auto"
! Resistance (Ω) !! Cutoff Frequency (kHz)!! Reasoning
|-
| 10k || 100 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=10kHz but not at 100kHz. Based on a rise time of approximately 0.01ms, the cutoff frequency can be estimated to be close to 100kHz.
|-
| 100k || 33 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=10kHz but not at 100kHz. Based on a rise time of approximately 0.03ms, the cutoff frequency can be estimated to be close to 30kHz.
|-
| 1M || 6 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=1kHz but not at 10kHz. Based on a rise time of approximately 0.15ms, the cutoff frequency can be estimated to be close to 7kHz.
|}

[[image: Optical_sensor_red.png|1000px|centre]]

Repeating the same analysis for the blue LED,

{| class="wikitable" style="margin:auto"
! Resistance (Ω) !! Cutoff Frequency (kHz)!! Reasoning
|-
| 10k || 500 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=10kHz but not at 100kHz. Based on a rise time of approximately 0.003ms, the cutoff frequency can be estimated to be ~300kHz.
|-
| 100k || 14 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=10kHz but not at 100kHz. Based on a rise time of approximately 0.04ms, the cutoff frequency can be estimated to be ~25kHz.
|-
| 1M || 6 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=1kHz but not at 10kHz. Based on a rise time of approximately 0.20ms, the cutoff frequency can be estimated to be close to 5kHz.
|}

[[image: Optical_sensor_blue.png|1000px|centre]]

Narrowing down to the specific frequency of 1kHz for blue LED for a clearer illustration, it can be shown that with decreasing external resistance, time constant decreases which replicates the signal sent into the LED (square wave). However, a lower resistance will entail lower signal-to-noise ratio. At the lower resistance of 10kΩ, the signal captured resembles a square wave while the higher resistance of 1MΩ shows, there is an evident decay in the rise and fall of the captured signal. Furthermore, the graphs also illustrate that the background noise is more prominent at lower resistance as the steady-state value across the lower resistance is smaller.

[[image: compare_resistance_blue_1kHz.png|400px|centre]]

For completeness of our discussion, the plots obtained from the measurements of the green LED is shown below. However, due to the low steady-state value of the voltage across the resistor, the rise time of the photodiode cannot be clearly determined.

[[image: Optical_sensor_green.png|1000px|centre]]

===Varying Wavelength===

From our experimental results, the photodiode has a faster response at longer wavelengths.
{| class="wikitable" style="margin:auto"
! LED!! Wavelength (nm) !! Resistance (Ω) !! Rise Time (ms) !! Remarks
|-
| Red || 643 ||10k || 0.01 ||
|-
| || || 100k || 0.03 ||
|-
| || || 1M || 0.16 ||
|-
| Green || 570 || 10k, 100k, 1M || N.A. || Low signal-to-noise ratio
|-
| Blue|| 450-495 || 10k || 0.002 ||
|-
| || || 100k || 0.07 ||
|-
| || || 1M || 0.18
|}

Out of the three LEDs used, the signal-to-noise ratio of the green LED is the lowest. Powering the three LEDs reveals that with the same voltage supplied, the green LED is the dimmest. Thus, the intensity of incident green light on the photodiode is significantly lower. The signal captured by the photodiode is lower and hence, the decrease in resistance of the photodiode is smaller. As a result, the voltage across the external resistor in the circuit of a fixed resistance is lower. Because of this, the change in voltage reading (in the switching of the LED) on the oscilloscope is closer to background noise. Thus, signal-to-noise ratio is lower.

[[image: LED_brightness.jpeg|300px|centre]]

Considering LEDs flickering at 100Hz, the following steady-state values for voltage across the external resistor were obtained.

For the Red LED,
{| class="wikitable" style="margin:auto"
! Resistance (Ω)!! Steady State Value (V)
|-
| 10k || 0.03
|-
| 100k || 0.40
|-
| 1M|| 2.16
|}

For the Blue LED,
{| class="wikitable" style="margin:auto"
! Resistance (Ω)!! Steady State Value (V)
|-
| 10k || 0.05
|-
| 100k || 0.47
|-
| 1M|| 2.44
|}

The steady-state value is dependent on the photosensitivity at different wavelengths and the brightness of the LED.

===Other Light Source(s)===
The photodiode is used to characterise the flickering of a computer screen. For this, we choose the 100kΩ resistor that gave us a sufficient characteristics and designed a compact circuit.

[[image:Final_design.jpeg|400px|center]]

Using the photodiode, we can determine that the Red LED was flickering at 1kHz, while the refresh rate of the computer screen was approximately 50kHz.
[[image:Flicker sources.png|400px|center]]

==[[Lab Log]]==

==References==
[1] NVC Lighting UK, Technical Support - What is Flicker in Relation to Lighting? https://www.nvcuk.com/technical-support/view/what-is-flicker-in-relation-to-lighting-2

[2] A. Wilkins, J. Veitch & B. Lehman. “LED lighting flicker and potential health concerns: IEEE standard PAR1789 update, “Energy Conversion Congress and Exposition, Atlanta Georgia, pp. 171-178, 2010

Optical Sensor for Noise Flickering

2024-04-17T03:52:32Z

Amanda: /* Equipment Needed */

==Group Members==
Eric Cheung Jun Hao; Lee An Min, Amanda; Loh Jia Ying Whitney

==Introduction and Background==
Flicker is the repeated and frequent variation in the output of light source over time. All light sources flicker but vary depending on several variables [1].

There are 4 features that have serious impact on the viewer [1]:

(1) Frequency

(2) Amplitude

(3) Wave form

(4) Light Intensity

The flicker effects can have adverse effects that impacts users as summarised by Wilkins in Table 1 [2]. As such, it is important to be able to detect frequencies when LED or sources of light fall within this range that can severely affect human functions, especially with the development of technology and use of such technology.

''Table 1: Flicker and its Biological Effects [2]''

[[image:Flicker_Bio_effect.jpeg]]

==Objective==

The objective of this project is to characterise a given photodiode and to successfully determine the frequency of an unknown flickering light source.

[[image:Optical_sensor_circuit.jpeg | 300px | none | left ]]
''Figure 1: Potential Divider Circuit''

With a simple potential divider, consisting a resistor and a photodiode in series, the resistance and hence sensitivity of the photodiode can be determined. The photodiode resistance is a function of light exposure, more specifically it is inversely proportional to light intensity. By exposing the photodiode to visual noise tags, such as the flickering of LEDs, the resistance across the photodiode is expected to decrease and hence, a larger potential can be measured across the resistor. The output can be observed on an oscilloscope to determine the performance of the photodiode.

==Set-Up==
===Equipment Needed===

''Table 2: List of Equipment Needed''
{| class="wikitable" style="margin:auto" |
! S/N !! Item !! Description/Model No.
|-
| 1 || Soldering Iron || -
|-
| 2 || Soldering Tin || -
|-
| 3 || Wires || -
|-
| 4 || Resistors || 10k, 100k, 1M
|-
| 5 || Photodiode || Hamamatsu S5972
|-
| 6 || DC Power Supply || Matrix MPS-3005L-3
|-
| 7 || Signal Generator || Agilent 33220A
|-
| 8 || 2GHz Digital Oscilloscope || LeCroy WaveRunner 203MXi-A
|}

''Table 3: Colour, Wavelength, and Size of LEDs Used''
{| class="wikitable" style="margin:auto" |
! LED S/N !! Colour !! Wavelength (nm) !! Size (mm)
|-
| 1 || Red || 643 || 5
|-
| 2 || Amber || 605 || 5
|-
| 3 || Green || 570 || 5
|-
| 4 || Blue || 450-495 || 5
|}

===Experimental Set-up===
Characterization of the photodiode is done with three 5 mm LEDs: (i) red, 643nm; (ii) green, 570nm; and (iii) blue, 450nm to 495nm. It can be noted that the photodiode sensitivity increases with increasing wavelength of LED used.

The photodiode used in this experiment is Hamamatsu S5972 Si PIN photodiode. According to the datasheet, it has a spectral response range between 320nm to 1000nm, with a peak sensitivity at 800nm, near infrared radiation. The cutoff frequency is 0.5GHz at reverse bias of 10V. The terminal capacitance at a reverse bias of 2V is close to 3pF.

[[image: Optical_sensor_complete_setup.jpeg|500px]][[image: Optical_sensor_setup_closeup.jpeg|500px]]

''Figure 2. Experimental Set-up (a) wide view, and (b) close-up view''

A signal generator is used to pulse the LEDs to create a flickering light source. A square wave with a peak-to-peak voltage of 2V is used across all the measurements taken. A DC power supply is used to supply 3V across the photodiode.

The performance of the photodiode will be determined by varying the following parameters: (i) wavelength of LED; (ii) external resistor in circuit; and (iii) frequency of LED blinking (1Hz - 100kHz).

The dependent variable that will be measured is the voltage reading across external resistor

This will allow us to determine the response of photodiode and efficiency (Time decay) of photodiode at different wavelengths.

==Timeline and Milestone==
{| class="wikitable" style="margin:auto"
! Week !! Dates !! Tasks
|-
| Week 7 || 4 - 8 Mar || Collecting equipment and prelimary set-up
|-
| Week 8 || 11 - 15 Mar || Complete circuit set-up and prelimary measurements
|-
| Week 9 || 18 - 22 Mar || Data collection (vary LEDs)
|-
| Week 10 || 25 - 29 Mar [Well-being day (28 Mar), Good Friday (29 Mar)]|| Data collection (vary resistance)
|-
| Week 11 || 1 - 5 Apr || Data Analysis and further measurements (if needed)
|-
| Week 12 || 8 - 12 Apr [Hari Raya (10 Apr)] || Data Analysis and explore other light sources (phone/computer screens)
|-
| Week 13 || 15 - 19 Apr || Analyse experimental results and complete documentation
|}

==Results==

===Varying External Resistance===

'''Relationship between resistance and cut-off frequency'''

It can be concluded that as external resistance increases, the cutoff frequency decreases. Decreasing the external resistance by one order of magnitude will increase the cut-off frequency by an order of magnitude. Hence, lower resistance needs to be used in order to measure at higher frequencies.

Comparing the results for red LED,

{| class="wikitable" style="margin:auto"
! Resistance (Ω) !! Cutoff Frequency (kHz)!! Reasoning
|-
| 10k || 100 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=10kHz but not at 100kHz. Based on a rise time of approximately 0.01ms, the cutoff frequency can be estimated to be close to 100kHz.
|-
| 100k || 33 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=10kHz but not at 100kHz. Based on a rise time of approximately 0.03ms, the cutoff frequency can be estimated to be close to 30kHz.
|-
| 1M || 6 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=1kHz but not at 10kHz. Based on a rise time of approximately 0.15ms, the cutoff frequency can be estimated to be close to 7kHz.
|}

[[image: Optical_sensor_red.png|1000px|centre]]

Repeating the same analysis for the blue LED,

{| class="wikitable" style="margin:auto"
! Resistance (Ω) !! Cutoff Frequency (kHz)!! Reasoning
|-
| 10k || 500 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=10kHz but not at 100kHz. Based on a rise time of approximately 0.003ms, the cutoff frequency can be estimated to be ~300kHz.
|-
| 100k || 14 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=10kHz but not at 100kHz. Based on a rise time of approximately 0.04ms, the cutoff frequency can be estimated to be ~25kHz.
|-
| 1M || 6 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=1kHz but not at 10kHz. Based on a rise time of approximately 0.20ms, the cutoff frequency can be estimated to be close to 5kHz.
|}

[[image: Optical_sensor_blue.png|1000px|centre]]

Narrowing down to the specific frequency of 1kHz for blue LED for a clearer illustration, it can be shown that with decreasing external resistance, time constant decreases which replicates the signal sent into the LED (square wave). However, a lower resistance will entail lower signal-to-noise ratio. At the lower resistance of 10kΩ, the signal captured resembles a square wave while the higher resistance of 1MΩ shows, there is an evident decay in the rise and fall of the captured signal. Furthermore, the graphs also illustrate that the background noise is more prominent at lower resistance as the steady-state value across the lower resistance is smaller.

[[image: compare_resistance_blue_1kHz.png|400px|centre]]

For completeness of our discussion, the plots obtained from the measurements of the green LED is shown below. However, due to the low steady-state value of the voltage across the resistor, the rise time of the photodiode cannot be clearly determined.

[[image: Optical_sensor_green.png|1000px|centre]]

===Varying Wavelength===

From our experimental results, the photodiode has a faster response at longer wavelengths.
{| class="wikitable" style="margin:auto"
! LED!! Wavelength (nm) !! Resistance (Ω) !! Rise Time (ms) !! Remarks
|-
| Red || 643 ||10k || 0.01 ||
|-
| || || 100k || 0.03 ||
|-
| || || 1M || 0.16 ||
|-
| Green || 570 || 10k, 100k, 1M || N.A. || Low signal-to-noise ratio
|-
| Blue|| 450-495 || 10k || 0.002 ||
|-
| || || 100k || 0.07 ||
|-
| || || 1M || 0.18
|}

Out of the three LEDs used, the signal-to-noise ratio of the green LED is the lowest. Powering the three LEDs reveals that with the same voltage supplied, the green LED is the dimmest. Thus, the intensity of incident green light on the photodiode is significantly lower. The signal captured by the photodiode is lower and hence, the decrease in resistance of the photodiode is smaller. As a result, the voltage across the external resistor in the circuit of a fixed resistance is lower. Because of this, the change in voltage reading (in the switching of the LED) on the oscilloscope is closer to background noise. Thus, signal-to-noise ratio is lower.

[[image: LED_brightness.jpeg|300px|centre]]

Considering LEDs flickering at 100Hz, the following steady-state values for voltage across the external resistor were obtained.

For the Red LED,
{| class="wikitable" style="margin:auto"
! Resistance (Ω)!! Steady State Value (V)
|-
| 10k || 0.03
|-
| 100k || 0.40
|-
| 1M|| 2.16
|}

For the Blue LED,
{| class="wikitable" style="margin:auto"
! Resistance (Ω)!! Steady State Value (V)
|-
| 10k || 0.05
|-
| 100k || 0.47
|-
| 1M|| 2.44
|}

The steady-state value is dependent on the photosensitivity at different wavelengths and the brightness of the LED.

===Other Light Source(s)===
The photodiode is used to characterise the flickering of a computer screen. For this, we choose the 100kΩ resistor that gave us a sufficient characteristics and designed a compact circuit.

[[image:Final_design.jpeg|400px|center]]

Using the photodiode, we can determine that the Red LED was flickering at 1kHz, while the refresh rate of the computer screen was approximately 50kHz.
[[image:Flicker sources.png|400px|center]]

==[[Lab Log]]==

==References==
[1] NVC Lighting UK, Technical Support - What is Flicker in Relation to Lighting? https://www.nvcuk.com/technical-support/view/what-is-flicker-in-relation-to-lighting-2

[2] A. Wilkins, J. Veitch & B. Lehman. “LED lighting flicker and potential health concerns: IEEE standard PAR1789 update, “Energy Conversion Congress and Exposition, Atlanta Georgia, pp. 171-178, 2010

Optical Sensor for Noise Flickering

2024-04-17T03:52:06Z

Amanda: /* Equipment Needed */

==Group Members==
Eric Cheung Jun Hao; Lee An Min, Amanda; Loh Jia Ying Whitney

==Introduction and Background==
Flicker is the repeated and frequent variation in the output of light source over time. All light sources flicker but vary depending on several variables [1].

There are 4 features that have serious impact on the viewer [1]:

(1) Frequency

(2) Amplitude

(3) Wave form

(4) Light Intensity

The flicker effects can have adverse effects that impacts users as summarised by Wilkins in Table 1 [2]. As such, it is important to be able to detect frequencies when LED or sources of light fall within this range that can severely affect human functions, especially with the development of technology and use of such technology.

''Table 1: Flicker and its Biological Effects [2]''

[[image:Flicker_Bio_effect.jpeg]]

==Objective==

The objective of this project is to characterise a given photodiode and to successfully determine the frequency of an unknown flickering light source.

[[image:Optical_sensor_circuit.jpeg | 300px | none | left ]]
''Figure 1. Potential Divider Circuit''

With a simple potential divider, consisting a resistor and a photodiode in series, the resistance and hence sensitivity of the photodiode can be determined. The photodiode resistance is a function of light exposure, more specifically it is inversely proportional to light intensity. By exposing the photodiode to visual noise tags, such as the flickering of LEDs, the resistance across the photodiode is expected to decrease and hence, a larger potential can be measured across the resistor. The output can be observed on an oscilloscope to determine the performance of the photodiode.

==Set-Up==
===Equipment Needed===

'''Table 2: List of Equipment Needed'''
{| class="wikitable" style="margin:auto" |
! S/N !! Item !! Description/Model No.
|-
| 1 || Soldering Iron || -
|-
| 2 || Soldering Tin || -
|-
| 3 || Wires || -
|-
| 4 || Resistors || 10k, 100k, 1M
|-
| 5 || Photodiode || Hamamatsu S5972
|-
| 6 || DC Power Supply || Matrix MPS-3005L-3
|-
| 7 || Signal Generator || Agilent 33220A
|-
| 8 || 2GHz Digital Oscilloscope || LeCroy WaveRunner 203MXi-A
|}

'''Table 3: Colour, Wavelength, and Size of LEDs Used'''
{| class="wikitable" style="margin:auto" |
! LED S/N !! Colour !! Wavelength (nm) !! Size (mm)
|-
| 1 || Red || 643 || 5
|-
| 2 || Amber || 605 || 5
|-
| 3 || Green || 570 || 5
|-
| 4 || Blue || 450-495 || 5
|}

===Experimental Set-up===
Characterization of the photodiode is done with three 5 mm LEDs: (i) red, 643nm; (ii) green, 570nm; and (iii) blue, 450nm to 495nm. It can be noted that the photodiode sensitivity increases with increasing wavelength of LED used.

The photodiode used in this experiment is Hamamatsu S5972 Si PIN photodiode. According to the datasheet, it has a spectral response range between 320nm to 1000nm, with a peak sensitivity at 800nm, near infrared radiation. The cutoff frequency is 0.5GHz at reverse bias of 10V. The terminal capacitance at a reverse bias of 2V is close to 3pF.

[[image: Optical_sensor_complete_setup.jpeg|500px]][[image: Optical_sensor_setup_closeup.jpeg|500px]]

A signal generator is used to pulse the LEDs to create a flickering light source. A square wave with a peak-to-peak voltage of 2V is used across all the measurements taken. A DC power supply is used to supply 3V across the photodiode.

The performance of the photodiode will be determined by varying the following parameters: (i) wavelength of LED; (ii) external resistor in circuit; and (iii) frequency of LED blinking (1Hz - 100kHz).

The dependent variable that will be measured is the voltage reading across external resistor

This will allow us to determine the response of photodiode and efficiency (Time decay) of photodiode at different wavelengths.

==Timeline and Milestone==
{| class="wikitable" style="margin:auto"
! Week !! Dates !! Tasks
|-
| Week 7 || 4 - 8 Mar || Collecting equipment and prelimary set-up
|-
| Week 8 || 11 - 15 Mar || Complete circuit set-up and prelimary measurements
|-
| Week 9 || 18 - 22 Mar || Data collection (vary LEDs)
|-
| Week 10 || 25 - 29 Mar [Well-being day (28 Mar), Good Friday (29 Mar)]|| Data collection (vary resistance)
|-
| Week 11 || 1 - 5 Apr || Data Analysis and further measurements (if needed)
|-
| Week 12 || 8 - 12 Apr [Hari Raya (10 Apr)] || Data Analysis and explore other light sources (phone/computer screens)
|-
| Week 13 || 15 - 19 Apr || Analyse experimental results and complete documentation
|}

==Results==

===Varying External Resistance===

'''Relationship between resistance and cut-off frequency'''

It can be concluded that as external resistance increases, the cutoff frequency decreases. Decreasing the external resistance by one order of magnitude will increase the cut-off frequency by an order of magnitude. Hence, lower resistance needs to be used in order to measure at higher frequencies.

Comparing the results for red LED,

{| class="wikitable" style="margin:auto"
! Resistance (Ω) !! Cutoff Frequency (kHz)!! Reasoning
|-
| 10k || 100 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=10kHz but not at 100kHz. Based on a rise time of approximately 0.01ms, the cutoff frequency can be estimated to be close to 100kHz.
|-
| 100k || 33 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=10kHz but not at 100kHz. Based on a rise time of approximately 0.03ms, the cutoff frequency can be estimated to be close to 30kHz.
|-
| 1M || 6 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=1kHz but not at 10kHz. Based on a rise time of approximately 0.15ms, the cutoff frequency can be estimated to be close to 7kHz.
|}

[[image: Optical_sensor_red.png|1000px|centre]]

Repeating the same analysis for the blue LED,

{| class="wikitable" style="margin:auto"
! Resistance (Ω) !! Cutoff Frequency (kHz)!! Reasoning
|-
| 10k || 500 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=10kHz but not at 100kHz. Based on a rise time of approximately 0.003ms, the cutoff frequency can be estimated to be ~300kHz.
|-
| 100k || 14 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=10kHz but not at 100kHz. Based on a rise time of approximately 0.04ms, the cutoff frequency can be estimated to be ~25kHz.
|-
| 1M || 6 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=1kHz but not at 10kHz. Based on a rise time of approximately 0.20ms, the cutoff frequency can be estimated to be close to 5kHz.
|}

[[image: Optical_sensor_blue.png|1000px|centre]]

Narrowing down to the specific frequency of 1kHz for blue LED for a clearer illustration, it can be shown that with decreasing external resistance, time constant decreases which replicates the signal sent into the LED (square wave). However, a lower resistance will entail lower signal-to-noise ratio. At the lower resistance of 10kΩ, the signal captured resembles a square wave while the higher resistance of 1MΩ shows, there is an evident decay in the rise and fall of the captured signal. Furthermore, the graphs also illustrate that the background noise is more prominent at lower resistance as the steady-state value across the lower resistance is smaller.

[[image: compare_resistance_blue_1kHz.png|400px|centre]]

For completeness of our discussion, the plots obtained from the measurements of the green LED is shown below. However, due to the low steady-state value of the voltage across the resistor, the rise time of the photodiode cannot be clearly determined.

[[image: Optical_sensor_green.png|1000px|centre]]

===Varying Wavelength===

From our experimental results, the photodiode has a faster response at longer wavelengths.
{| class="wikitable" style="margin:auto"
! LED!! Wavelength (nm) !! Resistance (Ω) !! Rise Time (ms) !! Remarks
|-
| Red || 643 ||10k || 0.01 ||
|-
| || || 100k || 0.03 ||
|-
| || || 1M || 0.16 ||
|-
| Green || 570 || 10k, 100k, 1M || N.A. || Low signal-to-noise ratio
|-
| Blue|| 450-495 || 10k || 0.002 ||
|-
| || || 100k || 0.07 ||
|-
| || || 1M || 0.18
|}

Out of the three LEDs used, the signal-to-noise ratio of the green LED is the lowest. Powering the three LEDs reveals that with the same voltage supplied, the green LED is the dimmest. Thus, the intensity of incident green light on the photodiode is significantly lower. The signal captured by the photodiode is lower and hence, the decrease in resistance of the photodiode is smaller. As a result, the voltage across the external resistor in the circuit of a fixed resistance is lower. Because of this, the change in voltage reading (in the switching of the LED) on the oscilloscope is closer to background noise. Thus, signal-to-noise ratio is lower.

[[image: LED_brightness.jpeg|300px|centre]]

Considering LEDs flickering at 100Hz, the following steady-state values for voltage across the external resistor were obtained.

For the Red LED,
{| class="wikitable" style="margin:auto"
! Resistance (Ω)!! Steady State Value (V)
|-
| 10k || 0.03
|-
| 100k || 0.40
|-
| 1M|| 2.16
|}

For the Blue LED,
{| class="wikitable" style="margin:auto"
! Resistance (Ω)!! Steady State Value (V)
|-
| 10k || 0.05
|-
| 100k || 0.47
|-
| 1M|| 2.44
|}

The steady-state value is dependent on the photosensitivity at different wavelengths and the brightness of the LED.

===Other Light Source(s)===
The photodiode is used to characterise the flickering of a computer screen. For this, we choose the 100kΩ resistor that gave us a sufficient characteristics and designed a compact circuit.

[[image:Final_design.jpeg|400px|center]]

Using the photodiode, we can determine that the Red LED was flickering at 1kHz, while the refresh rate of the computer screen was approximately 50kHz.
[[image:Flicker sources.png|400px|center]]

==[[Lab Log]]==

==References==
[1] NVC Lighting UK, Technical Support - What is Flicker in Relation to Lighting? https://www.nvcuk.com/technical-support/view/what-is-flicker-in-relation-to-lighting-2

[2] A. Wilkins, J. Veitch & B. Lehman. “LED lighting flicker and potential health concerns: IEEE standard PAR1789 update, “Energy Conversion Congress and Exposition, Atlanta Georgia, pp. 171-178, 2010

Optical Sensor for Noise Flickering

2024-04-16T03:52:14Z

Amanda:

==Group Members==
Eric Cheung Jun Hao; Lee An Min, Amanda; Loh Jia Ying Whitney

==Introduction and Background==
Flicker is the repeated and frequent variation in the output of light source over time. All light sources flicker but vary depending on several variables. [1]

There are 4 features that have serious impact on the viewer[1]:

(1) Frequency

(2) Amplitude

(3) Wave form

(4) Light Intensity

The flicker effects can have adverse effects that impacts users as summarised by Wilkins in the table below [2]. As such it is important to be able to detect frequencies when LED or sources of light fall within this range that can severely affect human functions especially with the development of technology and use of such technology.

Table 1: Flicker and its Biological Effects [2]

[[image:Flicker_Bio_effect.jpeg]]

==Objective==
The objective of this project is to characterise a given photodiode and to successfully determine the frequency of an unknown flickering light source.

[[image:Optical_sensor_circuit.jpeg]]

With a simple potential divider, consisting a resistor and a photodiode in series, the resistance and hence sensitivity of the photodiode can be determined. By exposing the photodiode to visual noise tags, such as the flickering of LEDs, the resistance across the photodiode is expected to decrease and hence, a larger potential can be measured across the resistor. The photodiode resistance is a function of light exposure. The resistance is inversely proportional to light intensity. The output can be observed on an oscilloscope to determine the performance of the photodiode.

==Set-Up==
===Equipment Needed===
{| class="wikitable" style="margin:auto" |
! S/N !! Item !! Description/Model No.
|-
| 1 || Soldering Iron || -
|-
| 2 || Soldering Tin || -
|-
| 3 || Wires || -
|-
| 4 || Resistors || 10k, 100k, 1M
|-
| 5 || Photodiode || Hamamatsu S5972
|-
| 6 || DC Power Supply || Matrix MPS-3005L-3
|-
| 7 || Signal Generator || Agilent 33220A
|-
| 8 || 2GHz Digital Oscilloscope || LeCroy WaveRunner 203MXi-A
|}

{| class="wikitable" style="margin:auto" |
! LED S/N !! Colour !! Wavelength (nm) !! Size (mm)
|-
| 1 || Red || 643 || 5
|-
| 2 || Amber || 605 || 5
|-
| 3 || Green || 570 || 5
|-
| 4 || Blue || 450-495 || 5
|}

===Experimental Set-up===
Characterization of the photodiode is done with three 5 mm LEDs: (i) red, 643nm; (ii) green, 570nm; and (iii) blue, 450nm to 495nm. It can be noted that the photodiode sensitivity increases with increasing wavelength of LED used.

The photodiode used in this experiment is Hamamatsu S5972 Si PIN photodiode. According to the datasheet, it has a spectral response range between 320nm to 1000nm, with a peak sensitivity at 800nm, near infrared radiation. The cutoff frequency is 0.5GHz at reverse bias of 10V. The terminal capacitance at reverse bias of 2V is close to 3pF.

[[image: Optical_sensor_complete_setup.jpeg|500px]][[image: Optical_sensor_setup_closeup.jpeg|500px]]

A signal generator is used to pulse the LEDs to create a flickering light source. A square wave with a peak-to-peak voltage of 2V is used across all the measurements taken. A DC power supply is used to supply 3V across the photodiode.

The performance of the photodiode will be determined by varying the following parameters: (i) wavelength of LED; (ii) external resistor in circuit; and (iii) frequency of LED blinking (1Hz - 100kHz).

The dependent variable that will be measured is the voltage reading across external resistor

This will allow us to determine the response of photodiode and efficiency (Time decay) of photodiode at different wavelengths.

==Timeline and Milestone==
{| class="wikitable" style="margin:auto"
! Week !! Dates !! Tasks
|-
| Week 7 || 4 - 8 Mar || Collecting equipment and prelimary set-up
|-
| Week 8 || 11 - 15 Mar || Complete circuit set-up and prelimary measurements
|-
| Week 9 || 18 - 22 Mar || Data collection (vary LEDs)
|-
| Week 10 || 25 - 29 Mar [Well-being day (28 Mar), Good Friday (29 Mar)]|| Data collection (vary resistance)
|-
| Week 11 || 1 - 5 Apr || Data Analysis and further measurements (if needed)
|-
| Week 12 || 8 - 12 Apr [Hari Raya (10 Apr)] || Data Analysis and explore other light sources (phone/computer screens)
|-
| Week 13 || 15 - 19 Apr || Analyse experimental results and complete documentation
|}

==Results==

===Varying External Resistance===

'''Relationship between resistance and cut-off frequency'''

It can be concluded that as external resistance increases, the cutoff frequency decreases. Decreasing the external resistance by one order of magnitude will increase the cut-off frequency by an order of magnitude. Hence, lower resistance needs to be used in order to measure at higher frequencies.

Comparing the results for red LED,

{| class="wikitable" style="margin:auto"
! Resistance (Ω) !! Cutoff Frequency (kHz)!! Reasoning
|-
| 10k || 100 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=10kHz but not at 100kHz. Based on a rise time of approximately 0.01ms, the cutoff frequency can be estimated to be close to 100kHz.
|-
| 100k || 33 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=10kHz but not at 100kHz. Based on a rise time of approximately 0.03ms, the cutoff frequency can be estimated to be close to 30kHz.
|-
| 1M || 6 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=1kHz but not at 10kHz. Based on a rise time of approximately 0.15ms, the cutoff frequency can be estimated to be close to 7kHz.
|}

[[image: Optical_sensor_red.png|1000px|centre]]

Repeating the same analysis for the blue LED,

{| class="wikitable" style="margin:auto"
! Resistance (Ω) !! Cutoff Frequency (kHz)!! Reasoning
|-
| 10k || 500 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=10kHz but not at 100kHz. Based on a rise time of approximately 0.003ms, the cutoff frequency can be estimated to be ~300kHz.
|-
| 100k || 14 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=10kHz but not at 100kHz. Based on a rise time of approximately 0.04ms, the cutoff frequency can be estimated to be ~25kHz.
|-
| 1M || 6 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=1kHz but not at 10kHz. Based on a rise time of approximately 0.20ms, the cutoff frequency can be estimated to be close to 5kHz.
|}

[[image: Optical_sensor_blue.png|1000px|centre]]

Narrowing down to the specific frequency of 1kHz for blue LED for a clearer illustration, it can be shown that with decreasing external resistance, time constant decreases which replicates the signal sent into the LED (square wave). However, a lower resistance will entail lower signal-to-noise ratio. At the lower resistance of 10kΩ, the signal captured resembles a square wave while the higher resistance of 1MΩ shows, there is an evident decay in the rise and fall of the captured signal. Furthermore, the graphs also illustrate that the background noise is more prominent at lower resistance as the steady-state value across the lower resistance is smaller.

[[image: compare_resistance_blue_1kHz.png|400px|centre]]

For completeness of our discussion, the plots obtained from the measurements of the green LED is shown below. However, due to the low steady-state value of the voltage across the resistor, the rise time of the photodiode cannot be clearly determined.

[[image: Optical_sensor_green.png|1000px|centre]]

===Varying Wavelength===

From our experimental results, the photodiode has a faster response at longer wavelengths.
{| class="wikitable" style="margin:auto"
! LED!! Wavelength (nm) !! Resistance (Ω) !! Rise Time (ms) !! Remarks
|-
| Red || 643 ||10k || 0.01 ||
|-
| || || 100k || 0.03 ||
|-
| || || 1M || 0.16 ||
|-
| Green || 570 || 10k, 100k, 1M || N.A. || Low signal-to-noise ratio
|-
| Blue|| 450-495 || 10k || 0.002 ||
|-
| || || 100k || 0.07 ||
|-
| || || 1M || 0.18
|}

Out of the three LEDs used, the signal-to-noise ratio of the green LED is the lowest. Powering the three LEDs reveals that with the same voltage supplied, the green LED is the dimmest. Thus, the intensity of incident green light on the photodiode is significantly lower. The signal captured by the photodiode is lower and hence, the decrease in resistance of the photodiode is smaller. As a result, the voltage across the external resistor in the circuit of a fixed resistance is lower. Because of this, the change in voltage reading (in the switching of the LED) on the oscilloscope is closer to background noise. Thus, signal-to-noise ratio is lower.

[[image: LED_brightness.jpeg|300px|centre]]

Considering LEDs flickering at 100Hz, the following steady-state values for voltage across the external resistor were obtained.

For the Red LED,
{| class="wikitable" style="margin:auto"
! Resistance (Ω)!! Steady State Value (V)
|-
| 10k || 0.03
|-
| 100k || 0.40
|-
| 1M|| 2.16
|}

For the Blue LED,
{| class="wikitable" style="margin:auto"
! Resistance (Ω)!! Steady State Value (V)
|-
| 10k || 0.05
|-
| 100k || 0.47
|-
| 1M|| 2.44
|}

The steady-state value is dependent on the photosensitivity at different wavelengths and the brightness of the LED.

===Other Light Source(s)===
The photodiode is used to characterise the flickering of a white computer screen. For this, we choose the 100kΩ resistor that gave us a sufficient characteristics and designed a compact circuit.

[[image:Final_design.jpeg|400px|center]]
==[[Lab Log]]==

==References==
[1] NVC Lighting UK, Technical Support - What is Flicker in Relation to Lighting? https://www.nvcuk.com/technical-support/view/what-is-flicker-in-relation-to-lighting-2

[2] A. Wilkins, J. Veitch & B. Lehman. “LED lighting flicker and potential health concerns: IEEE standard PAR1789 update, “Energy Conversion Congress and Exposition, Atlanta Georgia, pp. 171-178, 2010

Optical Sensor for Noise Flickering

2024-04-10T15:57:35Z

Amanda: /* Varying Wavelength */

==Group Members==
Eric Cheung Jun Hao; Lee An Min, Amanda; Loh Jia Ying Whitney

==Background and Introduction==

The objective of this project is to characterise a given photodiode and to successfully determine the frequency of an unknown flickering light source.

[[image:Optical_sensor_circuit.jpeg]]

With a simple potential divider, consisting a resistor and a photodiode in series, the resistance and hence sensitivity of the photodiode can be determined. By exposing the photodiode to visual noise tags, such as the flickering of LEDs, the resistance across the photodiode is expected to decrease and hence, a larger potential can be measured across the resistor. The photodiode resistance is a function of light exposure. The resistance is inversely proportional to light intensity. The output can be observed on an oscilloscope to determine the performance of the photodiode.

==Set-Up==
===Equipment Needed===
{| class="wikitable" style="margin:auto" |
! S/N !! Item !! Description/Model No.
|-
| 1 || Soldering Iron || -
|-
| 2 || Soldering Tin || -
|-
| 3 || Wires || -
|-
| 4 || Resistors || 10k, 100k, 1M
|-
| 5 || Photodiode || Hamamatsu S5972
|-
| 6 || DC Power Supply || Matrix MPS-3005L-3
|-
| 7 || Signal Generator || Agilent 33220A
|-
| 8 || 2GHz Digital Oscilloscope || LeCroy WaveRunner 203MXi-A
|}

{| class="wikitable" style="margin:auto" |
! LED S/N !! Colour !! Wavelength (nm) !! Size (mm)
|-
| 1 || Red || 643 || 5
|-
| 2 || Amber || 605 || 5
|-
| 3 || Green || 570 || 5
|-
| 4 || Blue || 450-495 || 5
|}

===Experimental Set-up===
Characterization of the photodiode is done with three 5 mm LEDs: (i) red, 643nm; (ii) green, 570nm; and (iii) blue, 450nm to 495nm. It can be noted that the photodiode sensitivity increases with increasing wavelength of LED used.

The photodiode used in this experiment is Hamamatsu S5972 Si PIN photodiode. According to the datasheet, it has a spectral response range between 320nm to 1000nm, with a peak sensitivity at 800nm, near infrared radiation. The cutoff frequency is 0.5GHz at reverse bias of 10V. The terminal capacitance at reverse bias of 2V is close to 3pF.

[[image: Optical_sensor_complete_setup.jpeg|500px]][[image: Optical_sensor_setup_closeup.jpeg|500px]]

A signal generator is used to pulse the LEDs to create a flickering light source. A square wave with a peak-to-peak voltage of 2V is used across all the measurements taken. A DC power supply is used to supply 3V across the photodiode.

The performance of the photodiode will be determined by varying the following parameters: (i) wavelength of LED; (ii) external resistor in circuit; and (iii) frequency of LED blinking (1Hz - 100kHz).

The dependent variable that will be measured is the voltage reading across external resistor

This will allow us to determine the following parameters (i) response of photodiode at different wavelengths; (ii) efficiency (Time decay) of photodiode at different wavelengths; and (iii) internal capacitance (time constant) of photodiode.

==Timeline and Milestone==
{| class="wikitable" style="margin:auto"
! Week !! Dates !! Tasks
|-
| Week 7 || 4 - 8 Mar || Collecting equipment and prelimary set-up
|-
| Week 8 || 11 - 15 Mar || Complete circuit set-up and prelimary measurements
|-
| Week 9 || 18 - 22 Mar || Data collection (vary LEDs)
|-
| Week 10 || 25 - 29 Mar [Well-being day (28 Mar), Good Friday (29 Mar)]|| Data collection (vary resistance)
|-
| Week 11 || 1 - 5 Apr || Data Analysis and further measurements (if needed)
|-
| Week 12 || 8 - 12 Apr [Hari Raya (10 Apr)] || Data Analysis and explore other light sources (phone/computer screens)
|-
| Week 13 || 15 - 19 Apr || Analyse experimental results and complete documentation
|}

==Results==

===Varying External Resistance===

'''Relationship between resistance and cut-off frequency'''

It can be concluded that as external resistance increases, the cutoff frequency decreases. Decreasing the external resistance by one order of magnitude will increase the cut-off frequency by an order of magnitude. Hence, lower resistance needs to be used in order to measure at higher frequencies.

Comparing the results for red LED,

{| class="wikitable" style="margin:auto"
! Resistance (Ω) !! Cutoff Frequency (kHz)!! Reasoning
|-
| 10k || 100 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=10kHz but not at 100kHz. Based on a rise time of approximately 0.01ms, the cutoff frequency can be estimated to be close to 100kHz.
|-
| 100k || 33 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=10kHz but not at 100kHz. Based on a rise time of approximately 0.03ms, the cutoff frequency can be estimated to be close to 30kHz.
|-
| 1M || 6 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=1kHz but not at 10kHz. Based on a rise time of approximately 0.15ms, the cutoff frequency can be estimated to be close to 7kHz.
|}

[[image: Optical_sensor_red.png|1000px|centre]]

Repeating the same analysis for the blue LED,

{| class="wikitable" style="margin:auto"
! Resistance (Ω) !! Cutoff Frequency (kHz)!! Reasoning
|-
| 10k || 500 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=10kHz but not at 100kHz. Based on a rise time of approximately 0.003ms, the cutoff frequency can be estimated to be ~300kHz.
|-
| 100k || 14 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=10kHz but not at 100kHz. Based on a rise time of approximately 0.04ms, the cutoff frequency can be estimated to be ~25kHz.
|-
| 1M || 6 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=1kHz but not at 10kHz. Based on a rise time of approximately 0.20ms, the cutoff frequency can be estimated to be close to 5kHz.
|}

[[image: Optical_sensor_blue.png|1000px|centre]]

Narrowing down to the specific frequency of 1kHz for blue LED for a clearer illustration, it can be shown that with decreasing external resistance, time constant decreases which replicates the signal sent into the LED (square wave). However, a lower resistance will entail lower signal-to-noise ratio. At the lower resistance of 10kΩ, the signal captured resembles a square wave while the higher resistance of 1MΩ shows, there is an evident decay in the rise and fall of the captured signal. Furthermore, the graphs also illustrate that the background noise is more prominent at lower resistance as the steady-state value across the lower resistance is smaller.

[[image: compare_resistance_blue_1kHz.png|400px|centre]]

For completeness of our discussion, the plots obtained from the measurements of the green LED is shown below. However, due to the low steady-state value of the voltage across the resistor, the rise time of the photodiode cannot be clearly determined.

[[image: Optical_sensor_green.png|1000px|centre]]

===Varying Wavelength===

From our experimental results, the photodiode has a faster response at longer wavelengths.
{| class="wikitable" style="margin:auto"
! LED!! Wavelength (nm) !! Resistance (Ω) !! Rise Time (ms) !! Remarks
|-
| Red || 643 ||10k || 0.01 ||
|-
| || || 100k || 0.03 ||
|-
| || || 1M || 0.16 ||
|-
| Green || 570 || 10k, 100k, 1M || N.A. || Low signal-to-noise ratio
|-
| Blue|| 450-495 || 10k || 0.002 ||
|-
| || || 100k || 0.07 ||
|-
| || || 1M || 0.18
|}

Out of the three LEDs used, the signal-to-noise ratio of the green LED is the lowest. Powering the three LEDs reveals that with the same voltage supplied, the green LED is the dimmest. Thus, the intensity of incident green light on the photodiode is significantly lower. The signal captured by the photodiode is lower and hence, the decrease in resistance of the photodiode is smaller. As a result, the voltage across the external resistor in the circuit of a fixed resistance is lower. Because of this, the change in voltage reading (in the switching of the LED) on the oscilloscope is closer to background noise. Thus, signal-to-noise ratio is lower.

[[image: LED_brightness.jpeg|300px|centre]]

Considering LEDs flickering at 100Hz, the following steady-state values for voltage across the external resistor were obtained.

For the Red LED,
{| class="wikitable" style="margin:auto"
! Resistance (Ω)!! Steady State Value (V)
|-
| 10k || 0.03
|-
| 100k || 0.40
|-
| 1M|| 2.16
|}

For the Blue LED,
{| class="wikitable" style="margin:auto"
! Resistance (Ω)!! Steady State Value (V)
|-
| 10k || 0.05
|-
| 100k || 0.47
|-
| 1M|| 2.44
|}

The steady-state value is dependent on the photosensitivity at different wavelengths and the brightness of the LED.

===Internal Capacitance===

The time constants for red and blue LEDs with different external resistance are determined experimentally. The time constant is related to the internal capacitance of the photodiode through the following equation,

𝜏 = RC

in which 𝜏 is the time constant, R is the external resistance, and C is the internal capacitance. From experimental results, the internal capacitance is calculated and shown in the table below.

{| class="wikitable" style="margin:auto" |
! LED !! Resistance (Ω) !! Time constant (ms) !! Internal Capacitance (nF)
|-
| Red || 10k || N.A. || N.A.
|-
| || 100k || 0.02 || 0.2
|-
| || 1M || 0.07|| 0.07
|-
| Blue || 10k|| N.A. || N.A.
|-
| || 100k|| 0.05 || 0.5
|-
| || 1M|| 0.09 || 0.09
|}

===Other Light Source(s)===
The photodiode is used to characterise the flickering of a white computer screen.

==[[Lab Log]]==

Optical Sensor for Noise Flickering

2024-04-10T15:56:21Z

Amanda: /* Internal Capacitance */

==Group Members==
Eric Cheung Jun Hao; Lee An Min, Amanda; Loh Jia Ying Whitney

==Background and Introduction==

The objective of this project is to characterise a given photodiode and to successfully determine the frequency of an unknown flickering light source.

[[image:Optical_sensor_circuit.jpeg]]

With a simple potential divider, consisting a resistor and a photodiode in series, the resistance and hence sensitivity of the photodiode can be determined. By exposing the photodiode to visual noise tags, such as the flickering of LEDs, the resistance across the photodiode is expected to decrease and hence, a larger potential can be measured across the resistor. The photodiode resistance is a function of light exposure. The resistance is inversely proportional to light intensity. The output can be observed on an oscilloscope to determine the performance of the photodiode.

==Set-Up==
===Equipment Needed===
{| class="wikitable" style="margin:auto" |
! S/N !! Item !! Description/Model No.
|-
| 1 || Soldering Iron || -
|-
| 2 || Soldering Tin || -
|-
| 3 || Wires || -
|-
| 4 || Resistors || 10k, 100k, 1M
|-
| 5 || Photodiode || Hamamatsu S5972
|-
| 6 || DC Power Supply || Matrix MPS-3005L-3
|-
| 7 || Signal Generator || Agilent 33220A
|-
| 8 || 2GHz Digital Oscilloscope || LeCroy WaveRunner 203MXi-A
|}

{| class="wikitable" style="margin:auto" |
! LED S/N !! Colour !! Wavelength (nm) !! Size (mm)
|-
| 1 || Red || 643 || 5
|-
| 2 || Amber || 605 || 5
|-
| 3 || Green || 570 || 5
|-
| 4 || Blue || 450-495 || 5
|}

===Experimental Set-up===
Characterization of the photodiode is done with three 5 mm LEDs: (i) red, 643nm; (ii) green, 570nm; and (iii) blue, 450nm to 495nm. It can be noted that the photodiode sensitivity increases with increasing wavelength of LED used.

The photodiode used in this experiment is Hamamatsu S5972 Si PIN photodiode. According to the datasheet, it has a spectral response range between 320nm to 1000nm, with a peak sensitivity at 800nm, near infrared radiation. The cutoff frequency is 0.5GHz at reverse bias of 10V. The terminal capacitance at reverse bias of 2V is close to 3pF.

[[image: Optical_sensor_complete_setup.jpeg|500px]][[image: Optical_sensor_setup_closeup.jpeg|500px]]

A signal generator is used to pulse the LEDs to create a flickering light source. A square wave with a peak-to-peak voltage of 2V is used across all the measurements taken. A DC power supply is used to supply 3V across the photodiode.

The performance of the photodiode will be determined by varying the following parameters: (i) wavelength of LED; (ii) external resistor in circuit; and (iii) frequency of LED blinking (1Hz - 100kHz).

The dependent variable that will be measured is the voltage reading across external resistor

This will allow us to determine the following parameters (i) response of photodiode at different wavelengths; (ii) efficiency (Time decay) of photodiode at different wavelengths; and (iii) internal capacitance (time constant) of photodiode.

==Timeline and Milestone==
{| class="wikitable" style="margin:auto"
! Week !! Dates !! Tasks
|-
| Week 7 || 4 - 8 Mar || Collecting equipment and prelimary set-up
|-
| Week 8 || 11 - 15 Mar || Complete circuit set-up and prelimary measurements
|-
| Week 9 || 18 - 22 Mar || Data collection (vary LEDs)
|-
| Week 10 || 25 - 29 Mar [Well-being day (28 Mar), Good Friday (29 Mar)]|| Data collection (vary resistance)
|-
| Week 11 || 1 - 5 Apr || Data Analysis and further measurements (if needed)
|-
| Week 12 || 8 - 12 Apr [Hari Raya (10 Apr)] || Data Analysis and explore other light sources (phone/computer screens)
|-
| Week 13 || 15 - 19 Apr || Analyse experimental results and complete documentation
|}

==Results==

===Varying External Resistance===

'''Relationship between resistance and cut-off frequency'''

It can be concluded that as external resistance increases, the cutoff frequency decreases. Decreasing the external resistance by one order of magnitude will increase the cut-off frequency by an order of magnitude. Hence, lower resistance needs to be used in order to measure at higher frequencies.

Comparing the results for red LED,

{| class="wikitable" style="margin:auto"
! Resistance (Ω) !! Cutoff Frequency (kHz)!! Reasoning
|-
| 10k || 100 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=10kHz but not at 100kHz. Based on a rise time of approximately 0.01ms, the cutoff frequency can be estimated to be close to 100kHz.
|-
| 100k || 33 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=10kHz but not at 100kHz. Based on a rise time of approximately 0.03ms, the cutoff frequency can be estimated to be close to 30kHz.
|-
| 1M || 6 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=1kHz but not at 10kHz. Based on a rise time of approximately 0.15ms, the cutoff frequency can be estimated to be close to 7kHz.
|}

[[image: Optical_sensor_red.png|1000px|centre]]

Repeating the same analysis for the blue LED,

{| class="wikitable" style="margin:auto"
! Resistance (Ω) !! Cutoff Frequency (kHz)!! Reasoning
|-
| 10k || 500 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=10kHz but not at 100kHz. Based on a rise time of approximately 0.003ms, the cutoff frequency can be estimated to be ~300kHz.
|-
| 100k || 14 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=10kHz but not at 100kHz. Based on a rise time of approximately 0.04ms, the cutoff frequency can be estimated to be ~25kHz.
|-
| 1M || 6 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=1kHz but not at 10kHz. Based on a rise time of approximately 0.20ms, the cutoff frequency can be estimated to be close to 5kHz.
|}

[[image: Optical_sensor_blue.png|1000px|centre]]

Narrowing down to the specific frequency of 1kHz for blue LED for a clearer illustration, it can be shown that with decreasing external resistance, time constant decreases which replicates the signal sent into the LED (square wave). However, a lower resistance will entail lower signal-to-noise ratio. At the lower resistance of 10kΩ, the signal captured resembles a square wave while the higher resistance of 1MΩ shows, there is an evident decay in the rise and fall of the captured signal. Furthermore, the graphs also illustrate that the background noise is more prominent at lower resistance as the steady-state value across the lower resistance is smaller.

[[image: compare_resistance_blue_1kHz.png|400px|centre]]

For completeness of our discussion, the plots obtained from the measurements of the green LED is shown below. However, due to the low steady-state value of the voltage across the resistor, the rise time of the photodiode cannot be clearly determined.

[[image: Optical_sensor_green.png|1000px|centre]]

===Varying Wavelength===

From our experimental results, the photodiode has a faster response at longer wavelengths.
{| class="wikitable" style="margin:auto"
! LED!! Wavelength (nm) !! Resistance (Ω) !! Rise Time (ms) !! Remarks
|-
| Red || 643 ||10k || 0.01 ||
|-
| || || 100k || 0.03 ||
|-
| || || 1M || 0.16 ||
|-
| Green || 570 || 10k, 100k, 1M || N.A. || Low signal-to-noise ratio
|-
| Blue|| 450-495 || 10k || 0.002 ||
|-
| || || 100k || 0.07 ||
|-
| || || 1M || 0.18
|}

Out of the three LEDs used, the signal-to-noise ratio of the green LED is the lowest. Powering the three LEDs reveals that with the same voltage supplied, the green LED is the dimmest. Thus, the intensity of incident green light on the photodiode is significantly lower. The signal captured by the photodiode is lower and hence, the decrease in resistance of the photodiode is smaller. As a result, the voltage across the external resistor in the circuit of a fixed resistance is lower. Because of this, the change in voltage reading (in the switching of the LED) on the oscilloscope is closer to background noise. Thus, signal-to-noise ratio is lower.

[[image: LED_brightness.jpeg|300px|centre]]

Considering LEDs flickering at 100Hz, the following steady-state values for voltage across the external resistor were obtained.

For the Red LED,
{| class="wikitable" style="margin:auto"
! Resistance (Ω)!! Steady State Value (V)
|-
| 10k || 0.04
|-
| 100k || 0.40
|-
| 1M|| 2.15
|}

For the Blue LED,
{| class="wikitable" style="margin:auto"
! Resistance (Ω)!! Steady State Value (V)
|-
| 10k || 0.05
|-
| 100k || 0.50
|-
| 1M|| 2.45
|}

The steady-state value is dependent on the photosensitivity at different wavelengths and the brightness of the LED.

===Internal Capacitance===

The time constants for red and blue LEDs with different external resistance are determined experimentally. The time constant is related to the internal capacitance of the photodiode through the following equation,

𝜏 = RC

in which 𝜏 is the time constant, R is the external resistance, and C is the internal capacitance. From experimental results, the internal capacitance is calculated and shown in the table below.

{| class="wikitable" style="margin:auto" |
! LED !! Resistance (Ω) !! Time constant (ms) !! Internal Capacitance (nF)
|-
| Red || 10k || N.A. || N.A.
|-
| || 100k || 0.02 || 0.2
|-
| || 1M || 0.07|| 0.07
|-
| Blue || 10k|| N.A. || N.A.
|-
| || 100k|| 0.05 || 0.5
|-
| || 1M|| 0.09 || 0.09
|}

===Other Light Source(s)===
The photodiode is used to characterise the flickering of a white computer screen.

==[[Lab Log]]==

Optical Sensor for Noise Flickering

2024-04-10T15:56:09Z

Amanda:

==Group Members==
Eric Cheung Jun Hao; Lee An Min, Amanda; Loh Jia Ying Whitney

==Background and Introduction==

The objective of this project is to characterise a given photodiode and to successfully determine the frequency of an unknown flickering light source.

[[image:Optical_sensor_circuit.jpeg]]

With a simple potential divider, consisting a resistor and a photodiode in series, the resistance and hence sensitivity of the photodiode can be determined. By exposing the photodiode to visual noise tags, such as the flickering of LEDs, the resistance across the photodiode is expected to decrease and hence, a larger potential can be measured across the resistor. The photodiode resistance is a function of light exposure. The resistance is inversely proportional to light intensity. The output can be observed on an oscilloscope to determine the performance of the photodiode.

==Set-Up==
===Equipment Needed===
{| class="wikitable" style="margin:auto" |
! S/N !! Item !! Description/Model No.
|-
| 1 || Soldering Iron || -
|-
| 2 || Soldering Tin || -
|-
| 3 || Wires || -
|-
| 4 || Resistors || 10k, 100k, 1M
|-
| 5 || Photodiode || Hamamatsu S5972
|-
| 6 || DC Power Supply || Matrix MPS-3005L-3
|-
| 7 || Signal Generator || Agilent 33220A
|-
| 8 || 2GHz Digital Oscilloscope || LeCroy WaveRunner 203MXi-A
|}

{| class="wikitable" style="margin:auto" |
! LED S/N !! Colour !! Wavelength (nm) !! Size (mm)
|-
| 1 || Red || 643 || 5
|-
| 2 || Amber || 605 || 5
|-
| 3 || Green || 570 || 5
|-
| 4 || Blue || 450-495 || 5
|}

===Experimental Set-up===
Characterization of the photodiode is done with three 5 mm LEDs: (i) red, 643nm; (ii) green, 570nm; and (iii) blue, 450nm to 495nm. It can be noted that the photodiode sensitivity increases with increasing wavelength of LED used.

The photodiode used in this experiment is Hamamatsu S5972 Si PIN photodiode. According to the datasheet, it has a spectral response range between 320nm to 1000nm, with a peak sensitivity at 800nm, near infrared radiation. The cutoff frequency is 0.5GHz at reverse bias of 10V. The terminal capacitance at reverse bias of 2V is close to 3pF.

[[image: Optical_sensor_complete_setup.jpeg|500px]][[image: Optical_sensor_setup_closeup.jpeg|500px]]

A signal generator is used to pulse the LEDs to create a flickering light source. A square wave with a peak-to-peak voltage of 2V is used across all the measurements taken. A DC power supply is used to supply 3V across the photodiode.

The performance of the photodiode will be determined by varying the following parameters: (i) wavelength of LED; (ii) external resistor in circuit; and (iii) frequency of LED blinking (1Hz - 100kHz).

The dependent variable that will be measured is the voltage reading across external resistor

This will allow us to determine the following parameters (i) response of photodiode at different wavelengths; (ii) efficiency (Time decay) of photodiode at different wavelengths; and (iii) internal capacitance (time constant) of photodiode.

==Timeline and Milestone==
{| class="wikitable" style="margin:auto"
! Week !! Dates !! Tasks
|-
| Week 7 || 4 - 8 Mar || Collecting equipment and prelimary set-up
|-
| Week 8 || 11 - 15 Mar || Complete circuit set-up and prelimary measurements
|-
| Week 9 || 18 - 22 Mar || Data collection (vary LEDs)
|-
| Week 10 || 25 - 29 Mar [Well-being day (28 Mar), Good Friday (29 Mar)]|| Data collection (vary resistance)
|-
| Week 11 || 1 - 5 Apr || Data Analysis and further measurements (if needed)
|-
| Week 12 || 8 - 12 Apr [Hari Raya (10 Apr)] || Data Analysis and explore other light sources (phone/computer screens)
|-
| Week 13 || 15 - 19 Apr || Analyse experimental results and complete documentation
|}

==Results==

===Varying External Resistance===

'''Relationship between resistance and cut-off frequency'''

It can be concluded that as external resistance increases, the cutoff frequency decreases. Decreasing the external resistance by one order of magnitude will increase the cut-off frequency by an order of magnitude. Hence, lower resistance needs to be used in order to measure at higher frequencies.

Comparing the results for red LED,

{| class="wikitable" style="margin:auto"
! Resistance (Ω) !! Cutoff Frequency (kHz)!! Reasoning
|-
| 10k || 100 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=10kHz but not at 100kHz. Based on a rise time of approximately 0.01ms, the cutoff frequency can be estimated to be close to 100kHz.
|-
| 100k || 33 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=10kHz but not at 100kHz. Based on a rise time of approximately 0.03ms, the cutoff frequency can be estimated to be close to 30kHz.
|-
| 1M || 6 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=1kHz but not at 10kHz. Based on a rise time of approximately 0.15ms, the cutoff frequency can be estimated to be close to 7kHz.
|}

[[image: Optical_sensor_red.png|1000px|centre]]

Repeating the same analysis for the blue LED,

{| class="wikitable" style="margin:auto"
! Resistance (Ω) !! Cutoff Frequency (kHz)!! Reasoning
|-
| 10k || 500 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=10kHz but not at 100kHz. Based on a rise time of approximately 0.003ms, the cutoff frequency can be estimated to be ~300kHz.
|-
| 100k || 14 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=10kHz but not at 100kHz. Based on a rise time of approximately 0.04ms, the cutoff frequency can be estimated to be ~25kHz.
|-
| 1M || 6 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=1kHz but not at 10kHz. Based on a rise time of approximately 0.20ms, the cutoff frequency can be estimated to be close to 5kHz.
|}

[[image: Optical_sensor_blue.png|1000px|centre]]

Narrowing down to the specific frequency of 1kHz for blue LED for a clearer illustration, it can be shown that with decreasing external resistance, time constant decreases which replicates the signal sent into the LED (square wave). However, a lower resistance will entail lower signal-to-noise ratio. At the lower resistance of 10kΩ, the signal captured resembles a square wave while the higher resistance of 1MΩ shows, there is an evident decay in the rise and fall of the captured signal. Furthermore, the graphs also illustrate that the background noise is more prominent at lower resistance as the steady-state value across the lower resistance is smaller.

[[image: compare_resistance_blue_1kHz.png|400px|centre]]

For completeness of our discussion, the plots obtained from the measurements of the green LED is shown below. However, due to the low steady-state value of the voltage across the resistor, the rise time of the photodiode cannot be clearly determined.

[[image: Optical_sensor_green.png|1000px|centre]]

===Varying Wavelength===

From our experimental results, the photodiode has a faster response at longer wavelengths.
{| class="wikitable" style="margin:auto"
! LED!! Wavelength (nm) !! Resistance (Ω) !! Rise Time (ms) !! Remarks
|-
| Red || 643 ||10k || 0.01 ||
|-
| || || 100k || 0.03 ||
|-
| || || 1M || 0.16 ||
|-
| Green || 570 || 10k, 100k, 1M || N.A. || Low signal-to-noise ratio
|-
| Blue|| 450-495 || 10k || 0.002 ||
|-
| || || 100k || 0.07 ||
|-
| || || 1M || 0.18
|}

Out of the three LEDs used, the signal-to-noise ratio of the green LED is the lowest. Powering the three LEDs reveals that with the same voltage supplied, the green LED is the dimmest. Thus, the intensity of incident green light on the photodiode is significantly lower. The signal captured by the photodiode is lower and hence, the decrease in resistance of the photodiode is smaller. As a result, the voltage across the external resistor in the circuit of a fixed resistance is lower. Because of this, the change in voltage reading (in the switching of the LED) on the oscilloscope is closer to background noise. Thus, signal-to-noise ratio is lower.

[[image: LED_brightness.jpeg|300px|centre]]

Considering LEDs flickering at 100Hz, the following steady-state values for voltage across the external resistor were obtained.

For the Red LED,
{| class="wikitable" style="margin:auto"
! Resistance (Ω)!! Steady State Value (V)
|-
| 10k || 0.04
|-
| 100k || 0.40
|-
| 1M|| 2.15
|}

For the Blue LED,
{| class="wikitable" style="margin:auto"
! Resistance (Ω)!! Steady State Value (V)
|-
| 10k || 0.05
|-
| 100k || 0.50
|-
| 1M|| 2.45
|}

The steady-state value is dependent on the photosensitivity at different wavelengths and the brightness of the LED.

===Internal Capacitance===

The time constants for red and blue LEDs with different external resistance are determined experimentally. The time constant is related to the internal capacitance of the photodiode through the following equation,

𝜏 = RC

in which 𝜏 is the time constant, R is the external resistance, and C is the internal capacitance. From experimental results, the internal capacitance is calculated and shown in the table below.

{| class="wikitable" style="margin:auto" |
! LED !! Resistance (Ω) !! Time constant (ms) !! Internal Capacitance (nF)
|-
| Red || 10k || N.A. || N.A.
|-
| || 100k || 0.02 || 0.2
|-
| || 1M || 0.07|| 0.07
|-
| Blue || 10k|| N.A. || N.A.
| || 100k|| 0.05 || 0.5
| || 1M|| 0.09 || 0.09
|}

===Other Light Source(s)===
The photodiode is used to characterise the flickering of a white computer screen.

==[[Lab Log]]==

Optical Sensor for Noise Flickering

2024-04-10T15:43:09Z

Amanda: /* Varying External Resistance */

==Group Members==
Eric Cheung Jun Hao; Lee An Min, Amanda; Loh Jia Ying Whitney

==Background and Introduction==

The objective of this project is to characterise a given photodiode and to successfully determine the frequency of an unknown flickering light source.

[[image:Optical_sensor_circuit.jpeg]]

With a simple potential divider, consisting a resistor and a photodiode in series, the resistance and hence sensitivity of the photodiode can be determined. By exposing the photodiode to visual noise tags, such as the flickering of LEDs, the resistance across the photodiode is expected to decrease and hence, a larger potential can be measured across the resistor. The photodiode resistance is a function of light exposure. The resistance is inversely proportional to light intensity. The output can be observed on an oscilloscope to determine the performance of the photodiode.

==Set-Up==
===Equipment Needed===
{| class="wikitable" style="margin:auto" |
! S/N !! Item !! Description/Model No.
|-
| 1 || Soldering Iron || -
|-
| 2 || Soldering Tin || -
|-
| 3 || Wires || -
|-
| 4 || Resistors || 10k, 100k, 1M
|-
| 5 || Photodiode || Hamamatsu S5972
|-
| 6 || DC Power Supply || Matrix MPS-3005L-3
|-
| 7 || Signal Generator || Agilent 33220A
|-
| 8 || 2GHz Digital Oscilloscope || LeCroy WaveRunner 203MXi-A
|}

{| class="wikitable" style="margin:auto" |
! LED S/N !! Colour !! Wavelength (nm) !! Size (mm)
|-
| 1 || Red || 643 || 5
|-
| 2 || Amber || 605 || 5
|-
| 3 || Green || 570 || 5
|-
| 4 || Blue || 450-495 || 5
|}

===Experimental Set-up===
Characterization of the photodiode is done with three 5 mm LEDs: (i) red, 643nm; (ii) green, 570nm; and (iii) blue, 450nm to 495nm. It can be noted that the photodiode sensitivity increases with increasing wavelength of LED used.

The photodiode used in this experiment is Hamamatsu S5972 Si PIN photodiode. According to the datasheet, it has a spectral response range between 320nm to 1000nm, with a peak sensitivity at 800nm, near infrared radiation. The cutoff frequency is 0.5GHz at reverse bias of 10V. The terminal capacitance at reverse bias of 2V is close to 3pF.

[[image: Optical_sensor_complete_setup.jpeg|500px]][[image: Optical_sensor_setup_closeup.jpeg|500px]]

A signal generator is used to pulse the LEDs to create a flickering light source. A square wave with a peak-to-peak voltage of 2V is used across all the measurements taken. A DC power supply is used to supply 3V across the photodiode.

The performance of the photodiode will be determined by varying the following parameters: (i) wavelength of LED; (ii) external resistor in circuit; and (iii) frequency of LED blinking (1Hz - 100kHz).

The dependent variable that will be measured is the voltage reading across external resistor

This will allow us to determine the following parameters (i) response of photodiode at different wavelengths; (ii) efficiency (Time decay) of photodiode at different wavelengths; and (iii) internal capacitance (time constant) of photodiode.

==Timeline and Milestone==
{| class="wikitable" style="margin:auto"
! Week !! Dates !! Tasks
|-
| Week 7 || 4 - 8 Mar || Collecting equipment and prelimary set-up
|-
| Week 8 || 11 - 15 Mar || Complete circuit set-up and prelimary measurements
|-
| Week 9 || 18 - 22 Mar || Data collection (vary LEDs)
|-
| Week 10 || 25 - 29 Mar [Well-being day (28 Mar), Good Friday (29 Mar)]|| Data collection (vary resistance)
|-
| Week 11 || 1 - 5 Apr || Data Analysis and further measurements (if needed)
|-
| Week 12 || 8 - 12 Apr [Hari Raya (10 Apr)] || Data Analysis and explore other light sources (phone/computer screens)
|-
| Week 13 || 15 - 19 Apr || Analyse experimental results and complete documentation
|}

==Results==

===Varying External Resistance===

'''Relationship between resistance and cut-off frequency'''

It can be concluded that as external resistance increases, the cutoff frequency decreases. Decreasing the external resistance by one order of magnitude will increase the cut-off frequency by an order of magnitude. Hence, lower resistance needs to be used in order to measure at higher frequencies.

Comparing the results for red LED,

{| class="wikitable" style="margin:auto"
! Resistance (Ω) !! Cutoff Frequency (kHz)!! Reasoning
|-
| 10k || 100 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=10kHz but not at 100kHz. Based on a rise time of approximately 0.01ms, the cutoff frequency can be estimated to be close to 100kHz.
|-
| 100k || 33 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=10kHz but not at 100kHz. Based on a rise time of approximately 0.03ms, the cutoff frequency can be estimated to be close to 30kHz.
|-
| 1M || 6 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=1kHz but not at 10kHz. Based on a rise time of approximately 0.15ms, the cutoff frequency can be estimated to be close to 7kHz.
|}

[[image: Optical_sensor_red.png|1000px|centre]]

Repeating the same analysis for the blue LED,

{| class="wikitable" style="margin:auto"
! Resistance (Ω) !! Cutoff Frequency (kHz)!! Reasoning
|-
| 10k || 500 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=10kHz but not at 100kHz. Based on a rise time of approximately 0.003ms, the cutoff frequency can be estimated to be ~300kHz.
|-
| 100k || 14 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=10kHz but not at 100kHz. Based on a rise time of approximately 0.04ms, the cutoff frequency can be estimated to be ~25kHz.
|-
| 1M || 6 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=1kHz but not at 10kHz. Based on a rise time of approximately 0.20ms, the cutoff frequency can be estimated to be close to 5kHz.
|}

[[image: Optical_sensor_blue.png|1000px|centre]]

Narrowing down to the specific frequency of 1kHz for blue LED for a clearer illustration, it can be shown that with decreasing external resistance, time constant decreases which replicates the signal sent into the LED (square wave). However, a lower resistance will entail lower signal-to-noise ratio. At the lower resistance of 10kΩ, the signal captured resembles a square wave while the higher resistance of 1MΩ shows, there is an evident decay in the rise and fall of the captured signal. Furthermore, the graphs also illustrate that the background noise is more prominent at lower resistance as the steady-state value across the lower resistance is smaller.

[[image: compare_resistance_blue_1kHz.png|400px|centre]]

For completeness of our discussion, the plots obtained from the measurements of the green LED is shown below. However, due to the low steady-state value of the voltage across the resistor, the rise time of the photodiode cannot be clearly determined.

[[image: Optical_sensor_green.png|1000px|centre]]

===Varying Wavelength===

From our experimental results, the photodiode has a faster response at longer wavelengths.
{| class="wikitable" style="margin:auto"
! LED!! Wavelength (nm) !! Resistance (Ω) !! Rise Time (ms) !! Remarks
|-
| Red || 643 ||10k || 0.01 ||
|-
| || || 100k || 0.03 ||
|-
| || || 1M || 0.16 ||
|-
| Green || 570 || 10k, 100k, 1M || N.A. || Low signal-to-noise ratio
|-
| Blue|| 450-495 || 10k || 0.002 ||
|-
| || || 100k || 0.07 ||
|-
| || || 1M || 0.18
|}

Out of the three LEDs used, the signal-to-noise ratio of the green LED is the lowest. Powering the three LEDs reveals that with the same voltage supplied, the green LED is the dimmest. Thus, the intensity of incident green light on the photodiode is significantly lower. The signal captured by the photodiode is lower and hence, the decrease in resistance of the photodiode is smaller. As a result, the voltage across the external resistor in the circuit of a fixed resistance is lower. Because of this, the change in voltage reading (in the switching of the LED) on the oscilloscope is closer to background noise. Thus, signal-to-noise ratio is lower.

[[image: LED_brightness.jpeg|300px|centre]]

Considering LEDs flickering at 100Hz, the following steady-state values for voltage across the external resistor were obtained.

For the Red LED,
{| class="wikitable" style="margin:auto"
! Resistance (Ω)!! Steady State Value (V)
|-
| 10k || 0.04
|-
| 100k || 0.40
|-
| 1M|| 2.15
|}

For the Blue LED,
{| class="wikitable" style="margin:auto"
! Resistance (Ω)!! Steady State Value (V)
|-
| 10k || 0.05
|-
| 100k || 0.50
|-
| 1M|| 2.45
|}

The steady-state value is dependent on the photosensitivity at different wavelengths and the brightness of the LED.

===Internal Capacitance===

The time constant of the photodiode with a series resistance of 100kΩ is ___. Thus, the internal capacitance of the photodiode is calculated to be ___.

===Other Light Source(s)===
The photodiode is used to characterise the flickering of a white computer screen.

==[[Lab Log]]==

Optical Sensor for Noise Flickering

2024-04-10T15:42:23Z

Amanda: /* Varying Wavelength */

==Group Members==
Eric Cheung Jun Hao; Lee An Min, Amanda; Loh Jia Ying Whitney

==Background and Introduction==

The objective of this project is to characterise a given photodiode and to successfully determine the frequency of an unknown flickering light source.

[[image:Optical_sensor_circuit.jpeg]]

With a simple potential divider, consisting a resistor and a photodiode in series, the resistance and hence sensitivity of the photodiode can be determined. By exposing the photodiode to visual noise tags, such as the flickering of LEDs, the resistance across the photodiode is expected to decrease and hence, a larger potential can be measured across the resistor. The photodiode resistance is a function of light exposure. The resistance is inversely proportional to light intensity. The output can be observed on an oscilloscope to determine the performance of the photodiode.

==Set-Up==
===Equipment Needed===
{| class="wikitable" style="margin:auto" |
! S/N !! Item !! Description/Model No.
|-
| 1 || Soldering Iron || -
|-
| 2 || Soldering Tin || -
|-
| 3 || Wires || -
|-
| 4 || Resistors || 10k, 100k, 1M
|-
| 5 || Photodiode || Hamamatsu S5972
|-
| 6 || DC Power Supply || Matrix MPS-3005L-3
|-
| 7 || Signal Generator || Agilent 33220A
|-
| 8 || 2GHz Digital Oscilloscope || LeCroy WaveRunner 203MXi-A
|}

{| class="wikitable" style="margin:auto" |
! LED S/N !! Colour !! Wavelength (nm) !! Size (mm)
|-
| 1 || Red || 643 || 5
|-
| 2 || Amber || 605 || 5
|-
| 3 || Green || 570 || 5
|-
| 4 || Blue || 450-495 || 5
|}

===Experimental Set-up===
Characterization of the photodiode is done with three 5 mm LEDs: (i) red, 643nm; (ii) green, 570nm; and (iii) blue, 450nm to 495nm. It can be noted that the photodiode sensitivity increases with increasing wavelength of LED used.

The photodiode used in this experiment is Hamamatsu S5972 Si PIN photodiode. According to the datasheet, it has a spectral response range between 320nm to 1000nm, with a peak sensitivity at 800nm, near infrared radiation. The cutoff frequency is 0.5GHz at reverse bias of 10V. The terminal capacitance at reverse bias of 2V is close to 3pF.

[[image: Optical_sensor_complete_setup.jpeg|500px]][[image: Optical_sensor_setup_closeup.jpeg|500px]]

A signal generator is used to pulse the LEDs to create a flickering light source. A square wave with a peak-to-peak voltage of 2V is used across all the measurements taken. A DC power supply is used to supply 3V across the photodiode.

The performance of the photodiode will be determined by varying the following parameters: (i) wavelength of LED; (ii) external resistor in circuit; and (iii) frequency of LED blinking (1Hz - 100kHz).

The dependent variable that will be measured is the voltage reading across external resistor

This will allow us to determine the following parameters (i) response of photodiode at different wavelengths; (ii) efficiency (Time decay) of photodiode at different wavelengths; and (iii) internal capacitance (time constant) of photodiode.

==Timeline and Milestone==
{| class="wikitable" style="margin:auto"
! Week !! Dates !! Tasks
|-
| Week 7 || 4 - 8 Mar || Collecting equipment and prelimary set-up
|-
| Week 8 || 11 - 15 Mar || Complete circuit set-up and prelimary measurements
|-
| Week 9 || 18 - 22 Mar || Data collection (vary LEDs)
|-
| Week 10 || 25 - 29 Mar [Well-being day (28 Mar), Good Friday (29 Mar)]|| Data collection (vary resistance)
|-
| Week 11 || 1 - 5 Apr || Data Analysis and further measurements (if needed)
|-
| Week 12 || 8 - 12 Apr [Hari Raya (10 Apr)] || Data Analysis and explore other light sources (phone/computer screens)
|-
| Week 13 || 15 - 19 Apr || Analyse experimental results and complete documentation
|}

==Results==

===Varying External Resistance===

'''Relationship between resistance and cut-off frequency'''

It can be concluded that as external resistance increases, the cutoff frequency decreases. Decreasing the external resistance by one order of magnitude will increase the cut-off frequency by an order of magnitude. Hence, lower resistance needs to be used in order to measure at higher frequencies.

Comparing the results for red LED,

{| class="wikitable" style="margin:auto"
! Resistance (Ω) !! Cutoff Frequency (kHz)!! Reasoning
|-
| 10k || ~100 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=10kHz but not at 100kHz. Based on a rise time of approximately 0.01ms, the cutoff frequency can be estimated to be close to 100kHz.
|-
| 100k || ~30 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=10kHz but not at 100kHz. Based on a rise time of approximately 0.03ms, the cutoff frequency can be estimated to be close to 30kHz.
|-
| 1M || ~7 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=1kHz but not at 10kHz. Based on a rise time of approximately 0.15ms, the cutoff frequency can be estimated to be close to 7kHz.
|}

[[image: Optical_sensor_red.png|1000px|centre]]

Repeating the same analysis for the blue LED,

{| class="wikitable" style="margin:auto"
! Resistance (Ω) !! Cutoff Frequency (kHz)!! Reasoning
|-
| 10k || ~300 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=10kHz but not at 100kHz. Based on a rise time of approximately 0.003ms, the cutoff frequency can be estimated to be ~300kHz.
|-
| 100k || ~25 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=10kHz but not at 100kHz. Based on a rise time of approximately 0.04ms, the cutoff frequency can be estimated to be ~25kHz.
|-
| 1M || ~5 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=1kHz but not at 10kHz. Based on a rise time of approximately 0.20ms, the cutoff frequency can be estimated to be close to 5kHz.
|}

[[image: Optical_sensor_blue.png|1000px|centre]]

Narrowing down to the specific frequency of 1kHz for blue LED for a clearer illustration, it can be shown that with decreasing external resistance, time constant decreases which replicates the signal sent into the LED (square wave). However, a lower resistance will entail lower signal-to-noise ratio. At the lower resistance of 10kΩ, the signal captured resembles a square wave while the higher resistance of 1MΩ shows, there is an evident decay in the rise and fall of the captured signal. Furthermore, the graphs also illustrate that the background noise is more prominent at lower resistance as the steady-state value across the lower resistance is smaller.

[[image: compare_resistance_blue_1kHz.png|400px|centre]]

For completeness of our discussion, the plots obtained from the measurements of the green LED is shown below. However, due to the low steady-state value of the voltage across the resistor, the rise time of the photodiode cannot be clearly determined.

[[image: Optical_sensor_green.png|1000px|centre]]

===Varying Wavelength===

From our experimental results, the photodiode has a faster response at longer wavelengths.
{| class="wikitable" style="margin:auto"
! LED!! Wavelength (nm) !! Resistance (Ω) !! Rise Time (ms) !! Remarks
|-
| Red || 643 ||10k || 0.01 ||
|-
| || || 100k || 0.03 ||
|-
| || || 1M || 0.16 ||
|-
| Green || 570 || 10k, 100k, 1M || N.A. || Low signal-to-noise ratio
|-
| Blue|| 450-495 || 10k || 0.002 ||
|-
| || || 100k || 0.07 ||
|-
| || || 1M || 0.18
|}

Out of the three LEDs used, the signal-to-noise ratio of the green LED is the lowest. Powering the three LEDs reveals that with the same voltage supplied, the green LED is the dimmest. Thus, the intensity of incident green light on the photodiode is significantly lower. The signal captured by the photodiode is lower and hence, the decrease in resistance of the photodiode is smaller. As a result, the voltage across the external resistor in the circuit of a fixed resistance is lower. Because of this, the change in voltage reading (in the switching of the LED) on the oscilloscope is closer to background noise. Thus, signal-to-noise ratio is lower.

[[image: LED_brightness.jpeg|300px|centre]]

Considering LEDs flickering at 100Hz, the following steady-state values for voltage across the external resistor were obtained.

For the Red LED,
{| class="wikitable" style="margin:auto"
! Resistance (Ω)!! Steady State Value (V)
|-
| 10k || 0.04
|-
| 100k || 0.40
|-
| 1M|| 2.15
|}

For the Blue LED,
{| class="wikitable" style="margin:auto"
! Resistance (Ω)!! Steady State Value (V)
|-
| 10k || 0.05
|-
| 100k || 0.50
|-
| 1M|| 2.45
|}

The steady-state value is dependent on the photosensitivity at different wavelengths and the brightness of the LED.

===Internal Capacitance===

The time constant of the photodiode with a series resistance of 100kΩ is ___. Thus, the internal capacitance of the photodiode is calculated to be ___.

===Other Light Source(s)===
The photodiode is used to characterise the flickering of a white computer screen.

==[[Lab Log]]==

Optical Sensor for Noise Flickering

2024-04-10T15:41:43Z

Amanda: /* Varying Wavelength */

==Group Members==
Eric Cheung Jun Hao; Lee An Min, Amanda; Loh Jia Ying Whitney

==Background and Introduction==

The objective of this project is to characterise a given photodiode and to successfully determine the frequency of an unknown flickering light source.

[[image:Optical_sensor_circuit.jpeg]]

With a simple potential divider, consisting a resistor and a photodiode in series, the resistance and hence sensitivity of the photodiode can be determined. By exposing the photodiode to visual noise tags, such as the flickering of LEDs, the resistance across the photodiode is expected to decrease and hence, a larger potential can be measured across the resistor. The photodiode resistance is a function of light exposure. The resistance is inversely proportional to light intensity. The output can be observed on an oscilloscope to determine the performance of the photodiode.

==Set-Up==
===Equipment Needed===
{| class="wikitable" style="margin:auto" |
! S/N !! Item !! Description/Model No.
|-
| 1 || Soldering Iron || -
|-
| 2 || Soldering Tin || -
|-
| 3 || Wires || -
|-
| 4 || Resistors || 10k, 100k, 1M
|-
| 5 || Photodiode || Hamamatsu S5972
|-
| 6 || DC Power Supply || Matrix MPS-3005L-3
|-
| 7 || Signal Generator || Agilent 33220A
|-
| 8 || 2GHz Digital Oscilloscope || LeCroy WaveRunner 203MXi-A
|}

{| class="wikitable" style="margin:auto" |
! LED S/N !! Colour !! Wavelength (nm) !! Size (mm)
|-
| 1 || Red || 643 || 5
|-
| 2 || Amber || 605 || 5
|-
| 3 || Green || 570 || 5
|-
| 4 || Blue || 450-495 || 5
|}

===Experimental Set-up===
Characterization of the photodiode is done with three 5 mm LEDs: (i) red, 643nm; (ii) green, 570nm; and (iii) blue, 450nm to 495nm. It can be noted that the photodiode sensitivity increases with increasing wavelength of LED used.

The photodiode used in this experiment is Hamamatsu S5972 Si PIN photodiode. According to the datasheet, it has a spectral response range between 320nm to 1000nm, with a peak sensitivity at 800nm, near infrared radiation. The cutoff frequency is 0.5GHz at reverse bias of 10V. The terminal capacitance at reverse bias of 2V is close to 3pF.

[[image: Optical_sensor_complete_setup.jpeg|500px]][[image: Optical_sensor_setup_closeup.jpeg|500px]]

A signal generator is used to pulse the LEDs to create a flickering light source. A square wave with a peak-to-peak voltage of 2V is used across all the measurements taken. A DC power supply is used to supply 3V across the photodiode.

The performance of the photodiode will be determined by varying the following parameters: (i) wavelength of LED; (ii) external resistor in circuit; and (iii) frequency of LED blinking (1Hz - 100kHz).

The dependent variable that will be measured is the voltage reading across external resistor

This will allow us to determine the following parameters (i) response of photodiode at different wavelengths; (ii) efficiency (Time decay) of photodiode at different wavelengths; and (iii) internal capacitance (time constant) of photodiode.

==Timeline and Milestone==
{| class="wikitable" style="margin:auto"
! Week !! Dates !! Tasks
|-
| Week 7 || 4 - 8 Mar || Collecting equipment and prelimary set-up
|-
| Week 8 || 11 - 15 Mar || Complete circuit set-up and prelimary measurements
|-
| Week 9 || 18 - 22 Mar || Data collection (vary LEDs)
|-
| Week 10 || 25 - 29 Mar [Well-being day (28 Mar), Good Friday (29 Mar)]|| Data collection (vary resistance)
|-
| Week 11 || 1 - 5 Apr || Data Analysis and further measurements (if needed)
|-
| Week 12 || 8 - 12 Apr [Hari Raya (10 Apr)] || Data Analysis and explore other light sources (phone/computer screens)
|-
| Week 13 || 15 - 19 Apr || Analyse experimental results and complete documentation
|}

==Results==

===Varying External Resistance===

'''Relationship between resistance and cut-off frequency'''

It can be concluded that as external resistance increases, the cutoff frequency decreases. Decreasing the external resistance by one order of magnitude will increase the cut-off frequency by an order of magnitude. Hence, lower resistance needs to be used in order to measure at higher frequencies.

Comparing the results for red LED,

{| class="wikitable" style="margin:auto"
! Resistance (Ω) !! Cutoff Frequency (kHz)!! Reasoning
|-
| 10k || ~100 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=10kHz but not at 100kHz. Based on a rise time of approximately 0.01ms, the cutoff frequency can be estimated to be close to 100kHz.
|-
| 100k || ~30 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=10kHz but not at 100kHz. Based on a rise time of approximately 0.03ms, the cutoff frequency can be estimated to be close to 30kHz.
|-
| 1M || ~7 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=1kHz but not at 10kHz. Based on a rise time of approximately 0.15ms, the cutoff frequency can be estimated to be close to 7kHz.
|}

[[image: Optical_sensor_red.png|1000px|centre]]

Repeating the same analysis for the blue LED,

{| class="wikitable" style="margin:auto"
! Resistance (Ω) !! Cutoff Frequency (kHz)!! Reasoning
|-
| 10k || ~300 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=10kHz but not at 100kHz. Based on a rise time of approximately 0.003ms, the cutoff frequency can be estimated to be ~300kHz.
|-
| 100k || ~25 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=10kHz but not at 100kHz. Based on a rise time of approximately 0.04ms, the cutoff frequency can be estimated to be ~25kHz.
|-
| 1M || ~5 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=1kHz but not at 10kHz. Based on a rise time of approximately 0.20ms, the cutoff frequency can be estimated to be close to 5kHz.
|}

[[image: Optical_sensor_blue.png|1000px|centre]]

Narrowing down to the specific frequency of 1kHz for blue LED for a clearer illustration, it can be shown that with decreasing external resistance, time constant decreases which replicates the signal sent into the LED (square wave). However, a lower resistance will entail lower signal-to-noise ratio. At the lower resistance of 10kΩ, the signal captured resembles a square wave while the higher resistance of 1MΩ shows, there is an evident decay in the rise and fall of the captured signal. Furthermore, the graphs also illustrate that the background noise is more prominent at lower resistance as the steady-state value across the lower resistance is smaller.

[[image: compare_resistance_blue_1kHz.png|400px|centre]]

For completeness of our discussion, the plots obtained from the measurements of the green LED is shown below. However, due to the low steady-state value of the voltage across the resistor, the rise time of the photodiode cannot be clearly determined.

[[image: Optical_sensor_green.png|1000px|centre]]

===Varying Wavelength===

From our experimental results, the photodiode has a faster response at longer wavelengths.
{| class="wikitable" style="margin:auto"
! LED!! Wavelength (nm) !! Resistance (Ω) !! Rise Time (ms) !! Remarks
|-
| Red || 643 ||10k || 0.01 ||
| || || 100k || 0.03 ||
| || || 1M || 0.16 ||
|-
| Green || 570 || 10k, 100k, 1M || N.A. || Low signal-to-noise ratio
|-
| Blue|| 450-495 || 10k || 0.002 ||
| || || 100k || 0.07 ||
| || || 1M || 0.18
|}

Out of the three LEDs used, the signal-to-noise ratio of the green LED is the lowest. Powering the three LEDs reveals that with the same voltage supplied, the green LED is the dimmest. Thus, the intensity of incident green light on the photodiode is significantly lower. The signal captured by the photodiode is lower and hence, the decrease in resistance of the photodiode is smaller. As a result, the voltage across the external resistor in the circuit of a fixed resistance is lower. Because of this, the change in voltage reading (in the switching of the LED) on the oscilloscope is closer to background noise. Thus, signal-to-noise ratio is lower.

[[image: LED_brightness.jpeg|300px|centre]]

Considering LEDs flickering at 100Hz, the following steady-state values for voltage across the external resistor were obtained.

For the Red LED,
{| class="wikitable" style="margin:auto"
! Resistance (Ω)!! Steady State Value (V)
|-
| 10k || 0.04
|-
| 100k || 0.40
|-
| 1M|| 2.15
|}

For the Blue LED,
{| class="wikitable" style="margin:auto"
! Resistance (Ω)!! Steady State Value (V)
|-
| 10k || 0.05
|-
| 100k || 0.50
|-
| 1M|| 2.45
|}

The steady-state value is dependent on the photosensitivity at different wavelengths and the brightness of the LED.

===Internal Capacitance===

The time constant of the photodiode with a series resistance of 100kΩ is ___. Thus, the internal capacitance of the photodiode is calculated to be ___.

===Other Light Source(s)===
The photodiode is used to characterise the flickering of a white computer screen.

==[[Lab Log]]==

Optical Sensor for Noise Flickering

2024-04-10T15:41:16Z

Amanda:

==Group Members==
Eric Cheung Jun Hao; Lee An Min, Amanda; Loh Jia Ying Whitney

==Background and Introduction==

The objective of this project is to characterise a given photodiode and to successfully determine the frequency of an unknown flickering light source.

[[image:Optical_sensor_circuit.jpeg]]

With a simple potential divider, consisting a resistor and a photodiode in series, the resistance and hence sensitivity of the photodiode can be determined. By exposing the photodiode to visual noise tags, such as the flickering of LEDs, the resistance across the photodiode is expected to decrease and hence, a larger potential can be measured across the resistor. The photodiode resistance is a function of light exposure. The resistance is inversely proportional to light intensity. The output can be observed on an oscilloscope to determine the performance of the photodiode.

==Set-Up==
===Equipment Needed===
{| class="wikitable" style="margin:auto" |
! S/N !! Item !! Description/Model No.
|-
| 1 || Soldering Iron || -
|-
| 2 || Soldering Tin || -
|-
| 3 || Wires || -
|-
| 4 || Resistors || 10k, 100k, 1M
|-
| 5 || Photodiode || Hamamatsu S5972
|-
| 6 || DC Power Supply || Matrix MPS-3005L-3
|-
| 7 || Signal Generator || Agilent 33220A
|-
| 8 || 2GHz Digital Oscilloscope || LeCroy WaveRunner 203MXi-A
|}

{| class="wikitable" style="margin:auto" |
! LED S/N !! Colour !! Wavelength (nm) !! Size (mm)
|-
| 1 || Red || 643 || 5
|-
| 2 || Amber || 605 || 5
|-
| 3 || Green || 570 || 5
|-
| 4 || Blue || 450-495 || 5
|}

===Experimental Set-up===
Characterization of the photodiode is done with three 5 mm LEDs: (i) red, 643nm; (ii) green, 570nm; and (iii) blue, 450nm to 495nm. It can be noted that the photodiode sensitivity increases with increasing wavelength of LED used.

The photodiode used in this experiment is Hamamatsu S5972 Si PIN photodiode. According to the datasheet, it has a spectral response range between 320nm to 1000nm, with a peak sensitivity at 800nm, near infrared radiation. The cutoff frequency is 0.5GHz at reverse bias of 10V. The terminal capacitance at reverse bias of 2V is close to 3pF.

[[image: Optical_sensor_complete_setup.jpeg|500px]][[image: Optical_sensor_setup_closeup.jpeg|500px]]

A signal generator is used to pulse the LEDs to create a flickering light source. A square wave with a peak-to-peak voltage of 2V is used across all the measurements taken. A DC power supply is used to supply 3V across the photodiode.

The performance of the photodiode will be determined by varying the following parameters: (i) wavelength of LED; (ii) external resistor in circuit; and (iii) frequency of LED blinking (1Hz - 100kHz).

The dependent variable that will be measured is the voltage reading across external resistor

This will allow us to determine the following parameters (i) response of photodiode at different wavelengths; (ii) efficiency (Time decay) of photodiode at different wavelengths; and (iii) internal capacitance (time constant) of photodiode.

==Timeline and Milestone==
{| class="wikitable" style="margin:auto"
! Week !! Dates !! Tasks
|-
| Week 7 || 4 - 8 Mar || Collecting equipment and prelimary set-up
|-
| Week 8 || 11 - 15 Mar || Complete circuit set-up and prelimary measurements
|-
| Week 9 || 18 - 22 Mar || Data collection (vary LEDs)
|-
| Week 10 || 25 - 29 Mar [Well-being day (28 Mar), Good Friday (29 Mar)]|| Data collection (vary resistance)
|-
| Week 11 || 1 - 5 Apr || Data Analysis and further measurements (if needed)
|-
| Week 12 || 8 - 12 Apr [Hari Raya (10 Apr)] || Data Analysis and explore other light sources (phone/computer screens)
|-
| Week 13 || 15 - 19 Apr || Analyse experimental results and complete documentation
|}

==Results==

===Varying External Resistance===

'''Relationship between resistance and cut-off frequency'''

It can be concluded that as external resistance increases, the cutoff frequency decreases. Decreasing the external resistance by one order of magnitude will increase the cut-off frequency by an order of magnitude. Hence, lower resistance needs to be used in order to measure at higher frequencies.

Comparing the results for red LED,

{| class="wikitable" style="margin:auto"
! Resistance (Ω) !! Cutoff Frequency (kHz)!! Reasoning
|-
| 10k || ~100 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=10kHz but not at 100kHz. Based on a rise time of approximately 0.01ms, the cutoff frequency can be estimated to be close to 100kHz.
|-
| 100k || ~30 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=10kHz but not at 100kHz. Based on a rise time of approximately 0.03ms, the cutoff frequency can be estimated to be close to 30kHz.
|-
| 1M || ~7 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=1kHz but not at 10kHz. Based on a rise time of approximately 0.15ms, the cutoff frequency can be estimated to be close to 7kHz.
|}

[[image: Optical_sensor_red.png|1000px|centre]]

Repeating the same analysis for the blue LED,

{| class="wikitable" style="margin:auto"
! Resistance (Ω) !! Cutoff Frequency (kHz)!! Reasoning
|-
| 10k || ~300 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=10kHz but not at 100kHz. Based on a rise time of approximately 0.003ms, the cutoff frequency can be estimated to be ~300kHz.
|-
| 100k || ~25 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=10kHz but not at 100kHz. Based on a rise time of approximately 0.04ms, the cutoff frequency can be estimated to be ~25kHz.
|-
| 1M || ~5 || Graphically, the voltage across the external resistor can reach and maintain at a steady-state value when f=1kHz but not at 10kHz. Based on a rise time of approximately 0.20ms, the cutoff frequency can be estimated to be close to 5kHz.
|}

[[image: Optical_sensor_blue.png|1000px|centre]]

Narrowing down to the specific frequency of 1kHz for blue LED for a clearer illustration, it can be shown that with decreasing external resistance, time constant decreases which replicates the signal sent into the LED (square wave). However, a lower resistance will entail lower signal-to-noise ratio. At the lower resistance of 10kΩ, the signal captured resembles a square wave while the higher resistance of 1MΩ shows, there is an evident decay in the rise and fall of the captured signal. Furthermore, the graphs also illustrate that the background noise is more prominent at lower resistance as the steady-state value across the lower resistance is smaller.

[[image: compare_resistance_blue_1kHz.png|400px|centre]]

For completeness of our discussion, the plots obtained from the measurements of the green LED is shown below. However, due to the low steady-state value of the voltage across the resistor, the rise time of the photodiode cannot be clearly determined.

[[image: Optical_sensor_green.png|1000px|centre]]

===Varying Wavelength===

From our experimental results, the photodiode has a faster response at longer wavelengths.
{| class="wikitable" style="margin:auto"
! LED!! Wavelength (nm) !! Resistance (Ω) !! Rise Time (ms) !! Remarks
|-
| Red || 643 ||10k || 0.01 ||
| || || 100k || 0.03 ||
| || || 1M || 0.16 ||
|-
| Green || 570 || 10k, 100k, 1M || N.A. || Low signal-to-noise ratio
|-
| Blue|| 450-495 || 10k || 0.002 ||
| || || 100k || 0.07 ||
| || || 1M || 0.18
|}

Out of the three LEDs used, the signal-to-noise ratio of the green LED is the lowest. Powering the three LEDs reveals that with the same voltage supplied, the green LED is the dimmest. Thus, the intensity of incident green light on the photodiode is significantly lower. The signal captured by the photodiode is lower and hence, the decrease in resistance of the photodiode is smaller. As a result, the voltage across the external resistor in the circuit of a fixed resistance is lower. Because of this, the change in voltage reading (in the switching of the LED) on the oscilloscope is closer to background noise. Thus, signal-to-noise ratio is lower.

[[image: LED_brightness.jpeg|300px|centre]]

Considering LEDs flickering at 100Hz, the following steady-state values for voltage across the external resistor were obtained.

For the Red LED,
{| class="wikitable" style="margin:auto"
! Resistance (Ω)!! Steady State Value (V)
|-
| 10k || 0.04
|-
| 100k || 0.40
|-
| 1M|| 2.15
|}

For the Blue LED,
{| class="wikitable" style="margin:auto"
! Resistance (Ω)!! Steady State Value (V)
|-
| 10k || 0.05
|-
| 100k || 0.50
|-
| 1M|| 2.45
|}

The steady-state value is dependent on the photosensitivity at different wavelengths and the brightness of the LED.

===Internal Capacitance===

The time constant of the photodiode with a series resistance of 100kΩ is ___. Thus, the internal capacitance of the photodiode is calculated to be ___.

===Other Light Source(s)===
The photodiode is used to characterise the flickering of a white computer screen.

==[[Lab Log]]==

Optical Sensor for Noise Flickering

2024-04-09T03:48:03Z

Amanda: /* Experimental Set-up */

Optical Sensor for Noise Flickering

2024-04-09T03:46:06Z

Amanda: /* Equipment Needed */

Optical Sensor for Noise Flickering

2024-04-09T03:43:57Z

Amanda:

Optical Sensor for Noise Flickering

2024-04-09T03:41:06Z

Amanda: /* Results */

Optical Sensor for Noise Flickering

2024-04-09T03:39:46Z

Amanda:

Optical Sensor for Noise Flickering

2024-04-09T03:39:18Z

Amanda:

Optical Sensor for Noise Flickering

2024-04-09T03:36:08Z

Amanda: /* Results */

Optical Sensor for Noise Flickering

2024-04-09T03:33:31Z

Amanda: /* Results */

Optical Sensor for Noise Flickering

2024-04-09T03:32:50Z

Amanda: /* Results */

Optical Sensor for Noise Flickering

2024-04-09T03:24:48Z

Amanda: /* Results */

Optical Sensor for Noise Flickering

2024-04-09T03:22:17Z

Amanda: /* Results */

Optical Sensor for Noise Flickering

2024-04-09T03:19:50Z

Amanda: /* Results */

Optical Sensor for Noise Flickering

2024-04-09T03:14:38Z

Amanda: /* Results */

Optical Sensor for Noise Flickering

2024-04-09T03:13:31Z

Amanda: /* Results */

Optical Sensor for Noise Flickering

2024-04-09T03:12:11Z

Amanda: /* Results */

Optical Sensor for Noise Flickering

2024-04-09T03:04:34Z

Amanda: /* Results */

Optical Sensor for Noise Flickering

2024-04-09T03:03:46Z

Amanda: /* Results */

Optical Sensor for Noise Flickering

2024-04-09T02:57:14Z

Amanda: /* Results */

Optical Sensor for Noise Flickering

2024-04-09T02:55:53Z

Amanda: /* Results */

Optical Sensor for Noise Flickering

2024-04-09T02:53:43Z

Amanda: /* Results */

Optical Sensor for Noise Flickering

2024-04-09T02:51:32Z

Amanda: /* Results */

Optical Sensor for Noise Flickering

2024-04-09T02:47:36Z

Amanda: /* Results */

Optical Sensor for Noise Flickering

2024-04-09T02:46:55Z

Amanda: /* Results */

Optical Sensor for Noise Flickering

2024-04-09T02:33:38Z

Amanda: /* Results */

Optical Sensor for Noise Flickering

2024-04-09T02:24:17Z

Amanda: /* Results */

Optical Sensor for Noise Flickering

2024-02-20T02:19:15Z

Amanda: /* [Set-Up] */

==Group Members==
Eric Cheung; Lee An Min, Amanda; Loh Jia Ying Whitney

==Summary==

==Set-Up==
===Equipment===
*Soldering Iron
*Soldering Tin
*Shrink Tubes
*Wires
*100k Ohm Resistor
*LDR Photoresistor: GL5528 / GL5537
*3V DC Power Supply
*OpenBCI Board

Optical Sensor for Noise Flickering

2024-02-20T02:19:07Z

Amanda: /* [Summary] */

==Group Members==
Eric Cheung; Lee An Min, Amanda; Loh Jia Ying Whitney

==Summary==

==[Set-Up]==
===[Equipment]===
*Soldering Iron
*Soldering Tin
*Shrink Tubes
*Wires
*100k Ohm Resistor
*LDR Photoresistor: GL5528 / GL5537
*3V DC Power Supply
*OpenBCI Board

Optical Sensor for Noise Flickering

2024-02-20T02:19:01Z

Amanda: /* [Group Members] */

==Group Members==
Eric Cheung; Lee An Min, Amanda; Loh Jia Ying Whitney

==[Summary]==

==[Set-Up]==
===[Equipment]===
*Soldering Iron
*Soldering Tin
*Shrink Tubes
*Wires
*100k Ohm Resistor
*LDR Photoresistor: GL5528 / GL5537
*3V DC Power Supply
*OpenBCI Board

Optical Sensor for Noise Flickering

2024-02-20T02:18:23Z

Amanda: Created page with "==[Group Members]== Eric Cheung; Lee An Min, Amanda; Loh Jia Ying Whitney ==[Summary]== ==[Set-Up]== ===[Equipment]=== *Soldering Iron *Soldering Tin *Shrink Tubes *Wires *100k Ohm Resistor *LDR Photoresistor: GL5528 / GL5537 *3V DC Power Supply *OpenBCI Board"

==[Group Members]==
Eric Cheung; Lee An Min, Amanda; Loh Jia Ying Whitney

==[Summary]==

==[Set-Up]==
===[Equipment]===
*Soldering Iron
*Soldering Tin
*Shrink Tubes
*Wires
*100k Ohm Resistor
*LDR Photoresistor: GL5528 / GL5537
*3V DC Power Supply
*OpenBCI Board

Main Page

2024-02-20T02:17:11Z

Amanda: /* Optical Sensor for Noise Flickerinng */

Welcome to the wiki page for the course PC5271: Physics of Sensors!

This is the repository where projects are documented. Creation of new accounts have now been blocked,and editing/creating pages is enabled. If you need an account, please contact Christian.

==Projects==
===[[Project 1 (Example)]]===
Keep a very brief description of a project or even a suggestion here, and perhaps the names of the team members, or who to contact if there is interest to join. Once the project has stabilized, keep stuff in the project page linked by the headline.

===[[Simple Optical Heart Rate Monitor]]===
This project demonstrates the principles of photoplethysmography (PPG) through the construction of a simple device to measure heart rate. The project involves using an LED and photodiode to detect variations in light absorption caused by changes in blood volume during each heartbeat.

===[[Gas sensor]]===
This project aims to use high and low detection methods of tin dioxide (SnO2) sensor to detect carbon monoxide or other combustible gases.

===[[Optical Sensor for Noise Flickering]]===
Group Members: Eric Cheung; Lee An Min, Amanda; Loh Jia Ying Whitney

This project aims to use a simple voltage divider made up with resistors and LDR to measure visual noise tags.

==Resources==
===Recorded sessions===
===Devices and material===
Apart form the stuff in the teaching lab, we have a resources you may want to consider for your project:
*...
===Books and links===
===Software===
* Various Python extensions. [https://www.python.org Python] is a very powerful free programming language that runs on just about any computer platform. It is open source and completely free.
* [https://www.gnuplot.info Gnuplot]: A free and very mature data display tool that works on just about any platform used that produces excellent publication-grade eps and pdf figures. Can be also used in scripts. Open source and completely free.
* Matlab: Very common, good toolset also for formal mathematics, good graphics. Expensive. We may have a site license, but I am not sure how painful it is for us to get a license for this course. Ask if interested.
* Mathematica: More common among theroetical physicists, very good in formal maths, now with better numerics. Graphs are ok but can be a pain to make looking good. As with Matlab, we do have a campus license. Ask if interested.

==Some wiki reference materials==
* [https://www.mediawiki.org/wiki/Special:MyLanguage/Manual:FAQ MediaWiki FAQ]
* [[Writing mathematical expressions]]
* [[Uploading images and files]]