detecting zero cross

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computer

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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
 

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

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