Had to make a new account, as couldn't find my old details! (Have been using other IC's for a few years!)
I'm doing a project, and want to communicate manually to my arduino from long distances.
It's essentially working on a project with telephone lines, and I would like to be able to identify when somebody manually sends basic 1/2 second pulses of Negative voltages of more than -12V up to -50v in order to change the state of the arduino.
Am happy with all aspects... except I'm not sure how to read negative voltages of such a magnitude safely without damaging the arduino.
I want to be able to do it with basic simple discrete components - IE Ceramic/Aluminium Capacitors and Resistors.
I don't need an exact measurement, I just want read "on/off".
Essentially if someone "taps 50v x number times" it will then run different programs.
Thank you very much for your ideas!