> Use a small bridge rectifier, where the output goes through a resister
> into an
> optocoupler.  The LED in the optocoupler will be on for mist of the wave,
> and
> only off just before each zero crossing, turning back on just after the
> zero
> crossing.
>
or just an optocoupler like the H11AAx, which has two diodes, designed
for AC detection. But either way, you'll still have a somewhat rounded
signal when the input voltage is close to the threshold of the diode. If
you really want a nice square wave, try a comparator/logic gate/transistor
after the opto to clean up the signal. Although I don't see why it can't
work with just the opto coupler...


Phil Eisermann
H:(440) 284-3787 (mazer@ix.netcom.com)
O:(440) 329-4680 (peiserma@ridgid.com)