Dear all,

I have a project that requires (among other things) that I trigger a new acquisition as soon as the 50Hz sine wave from the power line crosses zero (or 0° phase).
I found some ideas on the web using some comparators with OpAmps, but I wanted to know if there are devices already on the market.

Best regards,
Jean

 

There are many references. Search google for 'zero crossing detector'. Some microcontrollers have zero crossing detectors built in - PIC and Atmel for instance.

 

The circuit below should work pretty well for zero crossings in one direction. For both zero crossings per cycle you can use to opto couplers and tie the collectors together or "OR" the outputs.

Have to imagine that it would work better without the 1N4148, but people usually add parts for a reason. I suggest that if you try this circuit drive the optocoupler through a transformer for safety's sake.


http://electronics.stackexchange.com/questions/60435/zero-crossing-detector-do-i-really-need-the-7w-resistor

 

Many opto-isolators have built-in zero-cross detectors, for example these.

 

The circuit below should work pretty well for zero crossings in one direction. For both zero crossings per cycle you can use to opto couplers and tie the collectors together or "OR" the outputs.

Have to imagine that it would work better without the 1N4148, but people usually add parts for a reason. I suggest that if you try this circuit drive the optocoupler through a transformer for safety's sake.


http://electronics.stackexchange.co...ing-detector-do-i-really-need-the-7w-resistor

View attachment 116432

a reason. I suggest that if you try this circ

Hello,
Thank you for your message. I have seen this schematic and it should do the job. I am actually looking for a zero crossing in one direction, as I use the output signal to sync an acquisition card. Also, I will use a 1:1 transformer, as the input signal will be small (it will not be the actual 230V, but from a sensor attached to the 230V line). Any ideas on an actual 1:1 ot max. 5:1 transformer?
Regarding the optocoupler, I was thinking about the Vishay 4N25 (I originally went for the Vishay H11AA1, but it is in both directions, for me 1 direction is fine).

Again, thank you all for your replies.

Best regards,
Jean

 

Regarding the optocoupler, I was thinking about the Vishay 4N25

That is not a zero-cross detector type.

 

The circuit below should work pretty well for zero crossings in one direction. For both zero crossings per cycle you can use to opto couplers and tie the collectors together or "OR" the outputs.

Have to imagine that it would work better without the 1N4148, but people usually add parts for a reason. I suggest that if you try this circuit drive the optocoupler through a transformer for safety's sake.


http://electronics.stackexchange.co...ing-detector-do-i-really-need-the-7w-resistor

View attachment 116432

Depending on the amplitude of the input voltage, that diode might be very important to prevent a large reverse voltage from destroying the LED.

One concern I would have with this circuit is glitching at the switching points. With a 50 Hz input waveform, the output (which is analog) is going to be changing relatively slowly and so whatever it is driving may see lots of noisy transitions since there is no hysteresis. If nothing else, this should probably be followed by a comparator that has a Schmitt trigger input.