Rectified wave problem

Hi everyone;

I'm upto a triac control circuit . So , in order to control the triac triggering angle we need to detect the zero crossing points .. I've made the attached circuit schematic on a breadboard but I'm having too weird problem about the full wave rectified sine wave .. The rectified wave can not reach to zero cross twice but only once during a period and plots an unintended line as seen on the attached picture .. I've changed the circuit components for a thousands of times including the resistors , capacitors , bridge rectifiers , transistors even the breadboard ... The rectified wave even acts same on a single load resistor ...

What could the problem be ?

PLEASE HELP ... Attachment 7382Attachment 7383Attachment 7384Attachment 7385Attachment 7386

looks like your ac signal earth reference is biased one forward diode voltage above earth.
you need something like this

I use 'ac opto' to get 0xing. vary R3 to change width of the zero areaAttachment 7388

oh, add series resister to opto input !!

Quote:

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Originally Posted by amgen

I use 'ac opto' to get 0xing. vary R3 to change width of the zero areaAttachment 7388

oh, add series resister to opto input !!

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Thanks for your replies guys .

To amgen ; Why would we still need the diodes and the cap since the AC opto and a series resistor are sufficient to detect the zero crosses ?
I mean the following link would have sufficied I suppose ?

http://i.stack.imgur.com/sw3mO.png

thought that was part of your power supply stuff !! otherwise then not needed.
don