JP1 Remotes

[NEC1]

In a number of universal learning remotes with only one infrared emitter and no other infrared detector diode, I found that the infrared emitter can also act as an infrared detector with the right amplification circuitry (note that the infrared emitter in question has two pins).
An infrared emitter diode emits when a positive voltage is applied to its anode (input) via a limiting resistor with the cathode (output) being shunted to ground; however, an infrared emitter diode allows current to flow from cathode (input) to anode (output) if infrared light of sufficient intensity is directed at it.
I discovered this with a simple tool (for identifying the pins on infrared receiver modules) to try to identify my infrared LEDs if they were emitters or detectors.
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