Using two digital i/o pins a microprocessor can be used to both emit and detect light through a LED. The concept is simple, switch the biasing of the diode for each condition depending on the circuit layout of the diode. Since the LED is a photodiode, sensitive to light that is above the spectrum at which it displays, it can be polled for the current light level it sees.
Then you simulate the biasing of the LED in the microcontroller to emit and detect. Depending on the number of LEDs, even a low frequency uC could handle the job.
The video attached to the post demonstrates how fast and accurate this interface can operate. Also attached is a document on building a touch LED interface, where the above Figure clips were taken from. My immediate idea is a fun interactive light wall for advertisement. But the versatility of this simple input has no bounds. Buttons for a device, a simple touch screen, a hand reconfigurable digital sign, to just name a few possibilities. But does it work in the dark?
See also "Engineer's Notebooks" 1977, By Forrest M. Mins. Mins describes how an LED can be used as a photodiode.
Cabe
Attachments:
| TR2003-35.pdf | |
