wvmarle:
An optocoupler will allow you to read any voltage from 12V to 100V with a digital output. The main issue is the ringer which would be AC, so this needs a protection diode on the optocoupler. This should work:
R1 limits the current through the optocoupler (other optocouplers may need a different value), D1 protects against reverse voltage (the ringer - which will produce a 20 Hz block wave output).
Optocoupler is chosen based on what I happen to have in my parts box - no particular reason to go with this one instead of one of the many others.
I've tried this, and it should work (tested with breadboard and multimeter).
I measured current draw across the resistor (which I swapped out for a 5K6, for now, first one I found in box) and found it as 11ma for 60 volts.
What I didn't expect was the ridiculous amount of heat it gave of!
Burnt my fingers touching the damned thing, haha!
This doesn't seem normal for a 10ma draw, what am I doing wrong?
Also.... sorry to be a pest.... any suggestions for the protection diode? I don't want to end up ordering the wrong thing!