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university:courses:electronics:electronics-lab-led-sensor [24 Apr 2017 08:54] – rename Antoniu Miclausuniversity:courses:electronics:electronics-lab-led-sensor [24 Aug 2017 13:33] – add breadboard circuit + waveforms Antoniu Miclaus
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 In addition to emitting light, an LED can be used as a photodiode light sensor / detector. This capability may be used in a variety of applications including ambient light level sensor and bidirectional communications. As a photodiode, an LED is sensitive to wavelengths equal to or shorter than the predominant wavelength it emits. A green LED would be sensitive to blue light and to some green light, but not to yellow or red light. For example, a red LED will detect light emitted by a yellow LED and a yellow LED will detect light emitted by a green LED but a green LED will not detect light emitted by a red or yellow LED. All three LEDs will detect "white" light or light from a blue LED. White light contains a blue light component which can be detected by the green LED. Recall that visible light wavelengths can be listed from longest wavelength to shortest wavelength as Red, Orange, Yellow, Green, Blue, Indigo, Violet (remember the mnemonic "Roy G. Biv"). Violet is the shortest wavelength light with the most energetic photons and red has the longest wavelength light with the least energetic photons of all of the visible colors of light. LED's with clear plastic encapsulation will be more sensitive to broad-spectrum illumination (like general room lighting) than LED's with colored encapsulation (such as those included in the ADALP2000 Analog Parts Kit). In addition to emitting light, an LED can be used as a photodiode light sensor / detector. This capability may be used in a variety of applications including ambient light level sensor and bidirectional communications. As a photodiode, an LED is sensitive to wavelengths equal to or shorter than the predominant wavelength it emits. A green LED would be sensitive to blue light and to some green light, but not to yellow or red light. For example, a red LED will detect light emitted by a yellow LED and a yellow LED will detect light emitted by a green LED but a green LED will not detect light emitted by a red or yellow LED. All three LEDs will detect "white" light or light from a blue LED. White light contains a blue light component which can be detected by the green LED. Recall that visible light wavelengths can be listed from longest wavelength to shortest wavelength as Red, Orange, Yellow, Green, Blue, Indigo, Violet (remember the mnemonic "Roy G. Biv"). Violet is the shortest wavelength light with the most energetic photons and red has the longest wavelength light with the least energetic photons of all of the visible colors of light. LED's with clear plastic encapsulation will be more sensitive to broad-spectrum illumination (like general room lighting) than LED's with colored encapsulation (such as those included in the ADALP2000 Analog Parts Kit).
  
-To use the LED as an optical detector, do not forward bias the LED into quadrant #1 of the current-voltage (I-V) curve. (Quadrant 1 is when the operating voltage and current are both positive.) Allow the LED to operate in the solar cell mode, quadrant #4 (operating voltage is positive, current is negative), or in the photodiode mode quadrant #3 (operating voltage is positive, current is negative). In the solar cell mode, no applied bias voltage is used. The solar cell (or LED in this case) generates its own current and voltage.+To use the LED as an optical detector, do not forward bias the LED into quadrant #1 of the current-voltage (I-V) curve. (Quadrant 1 is when the operating voltage and current are both positive.) Allow the LED to operate in the solar cell mode, quadrant #4 (operating voltage is positive, current is negative), or in the photodiode mode quadrant #3 (operating voltage is negative, current is negative). In the solar cell mode, no applied bias voltage is used. The solar cell (or LED in this case) generates its own current and voltage.
  
 =====Materials:===== =====Materials:=====
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 Jumper wires\\ Jumper wires\\
 2 - 2N3904 NPN transistors ( or SSM2212 NPN matched pair )\\ 2 - 2N3904 NPN transistors ( or SSM2212 NPN matched pair )\\
-1 - 100KΩ resistor\\ +1 - 100KΩ resistor\\ 
-1 - 2.2KΩ resistor\\+1 - 2.2KΩ resistor\\
 3 - LEDs ( multiple red, yellow and green colors )\\ 3 - LEDs ( multiple red, yellow and green colors )\\
 1 - Infrared LED ( QED-123 ) 1 - Infrared LED ( QED-123 )
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 =====Hardware Setup:===== =====Hardware Setup:=====
 +
 +{{:university:courses:electronics:led_single_emitter-bb.png|}}
 +
 +<WRAP centeralign> Figure 2 LED and single common emitter NPN light sensor Breadboard Circuit </WRAP>
 +
 Use the variable positive power supply from the ADALM2000 module set to +5 V to power your circuit. Use scope channel 1 to monitor the voltage at the collector node of Q<sub>1</sub>. Use the variable positive power supply from the ADALM2000 module set to +5 V to power your circuit. Use scope channel 1 to monitor the voltage at the collector node of Q<sub>1</sub>.
  
 =====Procedure:===== =====Procedure:=====
  
-Insert a red, yellow or green LED into the circuit as shown one at a time. Try exposing the three different color LEDs from your ADALP2000 Analog Parts Kit to different light sources such as standard incandescent, florescent and LED lights held at differing distances from the LED sensor. Observe the voltage waveform seen at the collector of Q<sub>1</sub>. Try inserting the infrared LED from your kit and observing how it responds to the light from the different sources. Try increasing the sensitivity or gain by increasing the value of R<sub>L</sub> to 200KΩ or 470KΩ.+Insert a red, yellow or green LED into the circuit as shown one at a time. Try exposing the three different color LEDs from your ADALP2000 Analog Parts Kit to different light sources such as standard incandescent, florescent and LED lights held at differing distances from the LED sensor. Observe the voltage waveform seen at the collector of Q<sub>1</sub>. Try inserting the infrared LED from your kit and observing how it responds to the light from the different sources. Try increasing the sensitivity or gain by increasing the value of R<sub>L</sub> to 200KΩ or 470KΩ. 
 + 
 +{{:university:courses:electronics:led_single_emitter_wav1.png|}} 
 + 
 +<WRAP centeralign> Figure 3 Red LED and single common emitter NPN light sensor - Led light max distance </WRAP> 
 + 
 +{{:university:courses:electronics:led_single_emitter_wav2.png|}} 
 + 
 +<WRAP centeralign> Figure 4 Red LED and single common emitter NPN light sensor - Led light medium distance </WRAP> 
 + 
 +{{:university:courses:electronics:led_single_emitter_wav3.png|}} 
 + 
 +<WRAP centeralign> Figure 5 Red LED and single common emitter NPN light sensor - Led light min distance </WRAP> 
  
 =====Step 2 Directions:===== =====Step 2 Directions:=====
  
-Change the circuit on your breadboard to the Darlington configuration shown in figure 2. Be sure to turn off the power supply before making any changes to the circuit. With the Darlington connected transistors the emitter current of Q<sub>2</sub> becomes the base current of Q<sub>1</sub> such that the photo generated current from the LED D<sub>1</sub> is now multiplied by ß<sup>2</sup> and will appear in the load resistor R<sub>L</sub> from the collectors of Q<sub>1</sub> and Q<sub>2</sub>. Because of this much higher current gain we can use a much lower value load resistor.+Change the circuit on your breadboard to the Darlington configuration shown in figure 6. Be sure to turn off the power supply before making any changes to the circuit. With the Darlington connected transistors the emitter current of Q<sub>2</sub> becomes the base current of Q<sub>1</sub> such that the photo generated current from the LED D<sub>1</sub> is now multiplied by ß<sup>2</sup> and will appear in the load resistor R<sub>L</sub> from the collectors of Q<sub>1</sub> and Q<sub>2</sub>. Because of this much higher current gain we can use a much lower value load resistor. 
 + 
 +{{ :university:courses:electronics:aleds_f2.png?600 |}} 
 + 
 +<WRAP centeralign> Figure 6 LED and Darlington connected NPN light sensor </WRAP> 
 + 
 +=====Step 2 Hardware Setup:===== 
 + 
 +{{:university:courses:electronics:led_darlington-bb.png|}} 
 + 
 +<WRAP centeralign> Figure 7 LED and Darlington connected light sensor Breadboard Circuit </WRAP>
  
 =====Step 2 Procedure:===== =====Step 2 Procedure:=====
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 Repeat the same procedure of inserting the various LEDs into the circuit for D<sub>1</sub> and measuring the response to the various light sources and record them in your lab report. Repeat the same procedure of inserting the various LEDs into the circuit for D<sub>1</sub> and measuring the response to the various light sources and record them in your lab report.
  
-{{ :university:courses:electronics:aleds_f2.png?600 |}}+{{:university:courses:electronics:led_darlington_wav1.png|}} 
 + 
 +<WRAP centeralign> Figure 8 Red LED and Darlington connected light sensor - Led light max distance </WRAP> 
 + 
 +{{:university:courses:electronics:led_darlington_wav2.png|}} 
 + 
 +<WRAP centeralign> Figure 9 Red LED and Darlington connected light sensor - Led light medium distance </WRAP> 
 + 
 +{{:university:courses:electronics:led_darlington_wav3.png|}} 
 + 
 +<WRAP centeralign> Figure 10 Red LED and Darlington connected light sensor - Led light min distance </WRAP>
  
-<WRAP centeralign> Figure 2 LED and Darlington connected NPN light sensor </WRAP> 
  
 =====Questions:===== =====Questions:=====
university/courses/electronics/electronics-lab-led-sensor.txt · Last modified: 20 Nov 2023 04:55 by Eric hungerford

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