themotorman:
I have 112 switches that output a 0 or 5 volts. I need a way to send this to an Arduino, MEGA2560 , by the serial port, using some CMOS logic or? so that I can tell which switches have changed state. Normal condition is that all 112 are HI=5 volts. Ideas please. The Arduino and the switches are about 5 feet apart but in a noisy environment.
thanks
Well you state the switches already have a 0 or +5vdc signal value. Scanning 112 'dry contact' switches is pretty straight forward in simple 2D matrix scan using 22 arduino I/O pins, however if the switches already have a 'foreign' voltage (no free 'dry contacts') wired to them then it's not possible as the arduino has to be able to activate voltage on one dimension of the matrix to then read back the other dimension to tell is a specific switch is closed or not. So what are the switches now controlling and or wired too?
So assuming the switches are performing some electrical function already and you just want to 'monitor' their output states, then you probably need to use lots external logic chips like input shift registers (parallel in/serial out) or digital encoder chips (say lots of 16 in /1 out mux chips. It will not be a low parts count application that is for sure.
Lefty