Implementing bidirectional interface with a single common LED

It’s called LEDComm and requires only two pins of a microcontroller and a current limiting resistor to function. It works by making use of the fact that LEDs, once reverse biased, are also pretty efficient photodiodes, or light sensors.

Reversed biased LEDs can be modeled with a current source proportional to the light received, and a parallel capacitor. To read the amount of light the LED has received one must first charge the capacitor, and t

via Dangerous Prototype