120v zero cross detector

[Myren]

zero cross detector

i need some way to let my microcontroller know when a zero cross occurs, otherwise i cant keep phase with my little light dimming project.



i saw plans for using a 4n25 (the most primitive of optocouplers: merely a transistor pretty much), but i havent had much luck actually making it go. it pretty much just hooks the LED input up to the AC line then uses a pullup resistor off 5v on the other side to detect.

it triggers alright, but at ~60 khz, which just aint right.

been looking at some solutions: HCPL-3700 seems the best so far for its simplicity, and i /think/ it'll do what i want it to. the On semiconductor ca3059 and intersil fn490 both seem designed for what i want to do, plus a whole helluva ton more... major overkill. i'm afraid to even go check prices on them.

Myren

 

[cozturk]

zero cross

You need only ~1Mohm resistor from phase to pic.
see PICDIM Lamp Dimmer for the PIC12C508 from Microchip (PICREF-4)

 

[Myren]

zero cross detector optocoupler

Yeah, I was thinking about that. After much deliberation, I decided I definately need some sort of optocoupler in there though, I'm just not willing to place such a hazardous source anywhere near my micros. A pity, considering how convenient it would be.

You'd need to common ground your AC and digital too then, I'd presume? No floating voltages...

Thanks
Myren

 

[Gorilla]

zero crossing detector optocoupler

This design has a simple ZC detector, based on an optocoupler.
**broken link removed**

It's not my design, but it looks okay to me.