Arduino digital input, 80Vdc

Using Arduino General Electronics
10

I need to detect 0Vdc or >60Vdc (system on).

Assuming that you need isolation.

  1. Get the optocoupler's datasheet. Find the current needed to light up the led.
  2. Get a resistor that will generate that current under 60v. You can size that resistor a little bit higher if you want to make sure that there is sufficient threshold.
  3. If you want to protect the opto-coupler for reverse polarity, put a diode on it, or another opto-coupler but reverse the polarity - in that case, you can detect ac as well as dc.
  4. Done.