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i have a sinus voltage witch 5volt peak, and want to know when its zero volt.
Here we have 110VAC 50 or 60hz. Not 100hz. Not 5V.
The output is 0 or 5v to go to the computer.
I can build a circuit that works like this but you will get a (+)edge at one crossing and a (-)edge at the other.
This next circuit will give you a 200nS pulse (interrupt) at any zero crossing.
Now about phase:
In software you will need to measure the frequency. (you need to know 50 or 60hz) Depends on where you live.
Because you get two pulses/cycle then you really will get numbers like 100 or 120 hz.
10mS or 8.3mS
I do not know what you want to do and you are not going to say.....but
I will pretend you want to turn on a SCR like a lamp dimmer.
Measure from one pulse to another = 10 (8.3mS).
If you want the lamp at 1/2 power them after the interrupt, delay 5mS (4.15ms) and turn on the SCR.
This is how you set the phase. (measure time)