Zero Crossing Detection

[Gene Zumchak]

James,

    For safety, you use an optical couple with an appropriate series resistor and a
regular diode across the diode of the opto so that no appreciable reverse voltage
will appear across it.  Now take the output of the opto pulled up to five volts and
run the square wave into a CMOS exclusive OR gate.   Run direct to one input and a
high value resistor to the other input.  The input capacitance of the logic gate
together with the series resistor (try 100K) gives a delay.  The EXOR gate will
provide a pulse for both the rising edge and the falling edge.

Gene Z.


James Jackson wrote:

> Hi all - A bit off topic, but here goes -
>         I need to find out where I can get a schematic for a zero crossing
> detector that works with UK Mains voltages as an input. The voltage has an
> r.m.s. of 220-240v, and is at 50-60Hz. I just need a pulse output at logic
> levels each time the voltage crosses zero. This should make a pulsed output
> of 100Hz (correct me if I'm wrong). I know I could use a multivibrator, but
> I need the pulse to be in time with the mains supply of my device I'm making.
>
> Thanks,
> James Jackson.
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