Video Design Idea: LED senses and displays ambient-light intensity
Dhananjay V Gadre of India's Netaji Subhas Institute of Technology explains how an LED can double as a photosensor and a visual indicator of ambient-light intensity.
By Staff -- EDN, September 5, 2007
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This EDN Video Design Idea, presented by Dhananjay V Gadre, assistant professor in the electronics and communications engineering division of the Netaji Subhas Institute of Technology in New Delhi, India, shows a method of using an LED as a photovoltaic detector.
In addition, the circuit's microcontroller flashes the same LED at a frequency proportional to the incident light's intensity.
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Read more detail in "LED senses and displays ambient-light intensity" (This Design Idea appeared in written form in EDN in November 2006).
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View/download schematics:
Figure 1: Basic concept
Figure 2: LED-to-microcontroller pin connections
Figure 3: Detailed circuit diagram
Figure 4: Graph of circuit's square-wave output versus light intensity
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The LED type and color are variables to consider when using LEDs for ambient-light sensing. I found that IR LEDs work well, returning consistent values in repeated measured tests. The distraction of the LED blinking is also eliminated. Has anyone tried a UV LED?
John Krell - 2007-20-9 09:57:00 PDT -
The LED reversed biased during the measurement cycle. Subsequently, the LED is forward biased to indicate the sensed ambient intensity. Thus, the LED blinks at a rate proportional to the ambient light intensity; more the ambient light, higher is the LED blinking rate.
Dhananjay Gadre - 2007-15-9 20:35:00 PDT -
The LED is seems to be driven in the opposite direction to emit light. Is it a mistake or is it done on purpose. I suppose if your have to correct the polarity of the LED, will this trick still works? Have you done an actual testing or perhaps made a prototype out of the circuit?
Faulty Lee - 2007-12-9 14:57:00 PDT
