Hello,

I have a signal that I would like to monitor with pi and I'm not sure what is the best way to do this. The signal is pwm and its frequency is 100 Hz and the high value is oscillating between 10 - 20 VDC, so I would need to limit this high value to max. 3.3 VDC. I'm not sure how much amperage I can draw from the signal so it doesn't disturb it.

It is quite simple to do with a voltage divider and get the amperage quite low, but it's not the best solution for protecting the pi.

I did some calculating and I could do it with a 1.2k resistor and a 2V7 zener but when the signal is at 20 VDC it draws quite alot of amperage from it.

I also found Tage's solution for quite similar problem in and older post:

https://www.raspberrypi.org/forums/view ... hp?t=42938

This solution seems to be the best option so far although may be a little bit of an overkill.

Any ideas how I should approach this problem?