detecting zero cross

[computer]

hi,

what is the best way of detecting the zero cross on 240v 50Hz AC or 36v AC? I need to detect it for a PIC chip.

also, will it work if I send DC instead? I'm making a christmas light controller with 4 pic controlled triacs for dimming, etc. I will be making a few of the units if sucessful and would like 1 common design I can use for some 36v AC sets, and some 12v DC sets with the possibility of some 240v AC ones as well...

Thanks,
computer

 

[Styx]

pot it down with a resistor divider and use a comparator

 

[Nigel Goodwin]

hi,

what is the best way of detecting the zero cross on 240v 50Hz AC or 36v AC? I need to detect it for a PIC chip.

also, will it work if I send DC instead? I'm making a christmas light controller with 4 pic controlled triacs for dimming, etc. I will be making a few of the units if sucessful and would like 1 common design I can use for some 36v AC sets, and some 12v DC sets with the possibility of some 240v AC ones as well...

If you search on these forums there was a thread a little while ago, try .

As DC doesn't have a zero crossing point it's not relevent to DC control, you should use PWM instead.

 

[computer]

I know DC doesn't have a zero crossing point, but if I connected DC upto the zero crossing circuit its not going to short or anything? It just won't detect it and the code for that particular pic will just use a DC option with PWM...

 

[Sebi]

A possible solution...

 

[TheOne]

Is the output correct? During the -ve part of the input cycle the first transistor will be off, forcing the 2nd on and the output low not high? Output will be a square wave unless the input is taken from a full wave rectifier that have only +ve cycles

 

[Sebi]

Absolutely right, the quick draw not always good...
Correction