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# AC Sine Wave to Digital Pulse, plus Freq Multiplication

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First off, what is a reliable circuit to turn and AC sine wave into a digital pulse train? Voltage could be from 2-30VAC. I'm assuming you'd trigger a pulse whenever the AC voltage crosses 0.

Secondly, is there a good method to multiply the frequency of a digital square wave? How accurate would it be it the square wave was always changing frequency?

You need to be much specific about what you're wanting to do, it's too vague to answer as it is.

But squaring a sinewave is trivial, either a schmitt trigger, or an overdriven amplifier.

to multiply your square wave w, multiply it by 2 first to produce w2 by firing a pulse on every transition (xor the signal by a delayed version of it) then multiply w2 by 2 to produce w4 then divide w4 by 2 with a D flip to produce w42 which should be symmetric and track w

You need to be much specific about what you're wanting to do, it's too vague to answer as it is.

But squaring a sinewave is trivial, either a schmitt trigger, or an overdriven amplifier.
I have a rotating device with a reluctor wheel and sensor that generates AC. There are only 32 teeth on my wheel. I would like to be able to determine the position of the wheel with an accuracy 4 times higher than now (or 128 pulses per revolution). I will have an "event" which is a digital pulse. I want to know where my wheel is when this "event" occurs.

First method I thought of was the one I mentioned (pulse freq multiplication). I count the pulses and whatever the number is when my "event" pulse happens gives me my position.

The second would be to determine position based on time measurement. To do this I need to know RPM. Then I could measure how much time elapses between when one of the 32 teeth pass by and my "event" pulse to get the exact position. This seems much more complex and error prone to me as the elapsed time has to be calculated against RPM to get an accurate position.

Triggering a pulse whenever sine crosses zero will need only a zero crossing detector(zcd) cascaded with a monostable multivibrator.Now depending upon your need you can set the pulse width of o/p of monostable.You can use a RC network after ZCD for generating trigger for monostable.

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