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university:courses:electronics:electronics-lab-led-sensor [24 Apr 2017 08:54] – rename Antoniu Miclaus | university:courses:electronics:electronics-lab-led-sensor [20 Nov 2023 04:55] (current) – [Background:] Eric hungerford | ||
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- | ======Activity: | + | ======Activity: |
=====Objective: | =====Objective: | ||
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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 " | 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 " | ||
- | 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. | + | (Beware that phosphor-coated LEDs are increasingly common. These LEDs actually have a blue emitter, but a phosphor coating causes the blue light to be converted to any other color. If you try the following experiments with such an LED you may find very poor results lighting it from an identical LED, even though they appear to be of the same wavelength! Because, e.g., the blue LED, used as a photodiode, is being lit by the longer wavelegth orange phosphor.) |
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+ | 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:===== | ||
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+ | {{: | ||
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+ | <WRAP centeralign> | ||
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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< | 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< | ||
=====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, | + | 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, |
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+ | {{: | ||
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+ | <WRAP centeralign> | ||
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+ | {{: | ||
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+ | <WRAP centeralign> | ||
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+ | {{: | ||
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+ | <WRAP centeralign> | ||
=====Step 2 Directions: | =====Step 2 Directions: | ||
- | Change the circuit on your breadboard to the Darlington configuration shown in figure | + | Change the circuit on your breadboard to the Darlington configuration shown in figure |
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+ | {{ : | ||
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+ | <WRAP centeralign> | ||
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+ | =====Step 2 Hardware Setup: | ||
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+ | {{: | ||
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+ | <WRAP centeralign> | ||
=====Step 2 Procedure: | =====Step 2 Procedure: | ||
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Repeat the same procedure of inserting the various LEDs into the circuit for D< | Repeat the same procedure of inserting the various LEDs into the circuit for D< | ||
- | {{ : | + | {{: |
+ | |||
+ | <WRAP centeralign> | ||
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+ | {{: | ||
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+ | <WRAP centeralign> | ||
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+ | {{: | ||
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+ | <WRAP centeralign> | ||
- | <WRAP centeralign> | ||
=====Questions: | =====Questions: | ||
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How does the sensitivity of the Darlington connected configuration compare to the single common emitter configuration? | How does the sensitivity of the Darlington connected configuration compare to the single common emitter configuration? | ||
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+ | <WRAP round download> | ||
+ | **Resources: | ||
+ | * Fritzing files: [[downgit> | ||
+ | * LTspice files: [[downgit> | ||
+ | </ | ||
**For Further Reading:** | **For Further Reading:** |