Zero-crossing detector?

[ardhuru]

Thats a good circuit Don, but i'd also use a 47E resistor in series with the 0.1 uf cap.

Anand

[RussMartin]

I guess I wasn't very clear . . .

I don't need a transformerless power supply for the PIC circuit and associated glue; I was looking just for a transformerless zero-crossing detector.

[sougata]

Hi,

You can also use a NPN inverter from the rectified DC for sharper (inverted zero cross).

[The Master]

Recently ive been using this idea. That page describes how to run an LED from the mains but with just the capacitor and resistor you can run an AC input darlington opto. Ive been using this method for detecting the presence of AC but it should work fine to detecting a zero crossing too.

I always use an opto for safety. I did try a huge resistor feeding directly into the PIC which seemed to work fine till i connected the PIC to my laptop through serial and the laptop turned itself off.

My prefered method is to use the 12V coming from the supply transformer. If you can use a transformer for the supply then you only need 2 extra diodes and a resistor to feed into the PIC.

As for the code, i dont like using oninterrupt but i do use the interrupt flags. The program doesnt have to check the interrupt after each command that way. It checks it when you want.

[sougata]

Hi,

The zero-cross sensing is mostly used for phase angle control. The Master The circuit you mentioned would essentially phase shift the zero cross signal.

BTW if you replace this idea with this idea then you get more ideas. Like this idea

Thanks to the author of the site and The Master

[dhouston]

I always use an opto for safety. I did try a huge resistor feeding directly into the PIC which seemed to work fine till i connected the PIC to my laptop through serial and the laptop turned itself off.

For ZC, the resistor is adequate given the PIC has clamp diodes on the inputs. If you need mains isolation for RS232, use optos in the RS232 lines.

• http://www.pkfamily.com/users/solson/eeg/isoRS232.gif