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university:courses:electronics:electronics-lab-led-sensor [27 Mar 2017 16:51] – [Hardware Setup:] Doug Mercer | university:courses:electronics:electronics-lab-led-sensor [24 Apr 2017 08:54] – rename Antoniu Miclaus | ||
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When exposed to light photodiodes produce a current that is directly proportional to the intensity of the light. This light generated current flows in the opposite direction to current in a normal diode or LED. As more photons hit the photodiode the current increases causing a voltage across the diode. As the voltage across the diode increases the linearity decreases. | When exposed to light photodiodes produce a current that is directly proportional to the intensity of the light. This light generated current flows in the opposite direction to current in a normal diode or LED. As more photons hit the photodiode the current increases causing a voltage across the diode. As the voltage across the diode increases the linearity decreases. | ||
- | 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. | 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. | ||
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=====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 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 |
=====Step 2 Directions: | =====Step 2 Directions: |