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Please help me RECTIFY this problem :)

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New Member
Hello all,

I need detect the zero crossings of a 120V ac signal and act on it.

So far I have a transformer that converts the 120V to 12V (500mA).
I have the signal going into a rectifier (4 4001 diodes in a diamond shape - I think it's called a full wave rectifier...

anyway... the output is full wave recified... is there any circuitry anyone can suggest to turn this into a nice square wave where it goes high/low on a zero cross?

will a schmitt or something? or an H11L1?


New Member
(I also replied in the general section)

thank you ron, I do have an alternate source for dc, can you please post the simpler circuits? :)

basically I want to do 2 things:

1. use the 555 to control the intensity of a 120V ac light bulb (or small motor)

2. use a PIC microcontroller to control the intensity of the same thing...

I want to start with the 555 and than move on to using a microcontroller instead...
I have a question: do you need to detect the zero crossings and make sure the pulses start on the zero crossings? Can you clarify exactly what a triac is actually doing??

Any help would be greatly appreciated
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