Zero-Crossing question

[financecatalyst]

Can someone please guide me to any circuit to provide the following Square wave with 240V AC (with full wave rectification) input using minimum number of components.

[Dave]

How about an bidirectional opto isolator and a resisror?

Dave Purola,

[sayzer]

Click this link:

Zero-Crossing-Concept-Using-Optocoupler-GPIO-Change-Int-and-DT-s-Instant-Interrupt

[Ioannis]

My concern is for the heat dissipation from the 5W resistor.

Maybe the secondary of the tranformer can be used with lower waste of energy.

Ioannis

[financecatalyst]

I don't have transformer in the circuit. To cut costs, minimum components are required and as this is an enclosed circuit, it is ok to not to have isolation.
I previously used this-----
From Mains - > 2.2M->12v Zener-> 4.7k -> 5V Zener -> 4.4M -> PIC. This worked fine for a long time, but now I want to make the circuit better and put full wave rectification, I tried the same above circuit but the voltage on PIC is sticking to 0.5 for some reason. So I would like to ask if I should make changes to the above circuit may be reducing resistance values or choose a completely different circuit.

[sayzer]

My concern is for the heat dissipation from the 5W resistor.

Maybe the secondary of the tranformer can be used with lower waste of energy.

Ioannis

The circuit in the link is a concept.
Designer can work around it.

And yes; a transformer say with a 9V secondary, can also work.
In that case, have the zero cross input from there.

If no transformer will be used, then transformerless power supply concept can also work.
Long missed Melanie had a post for transformerless power supply here post #5.
You may get some ideas from her schematic.