How to detect Line Voltage

[HenrikOlsson]

And, if you use an opto with just one diode, your series resistor would heat up even less

Nah, be careful there. In that case you'll need an external diode across the LED in the isolator since the LED can only take a couple of volts (6V for the PC817) in the reverse direction and then the current going thru that diode will have to go thru the resistor(s) as well. That's the main reason I suggested the dual LED isolator.

If the PIC is isolated you could live with a voltage divider and a zener and then direct to the PIC input.

/Henrik.

[Ioannis]

Anand: I have to make an extended research for the opto coupler that need the less current.

Henrik: unfortunately it will not be isolated. The voltage divider would be a good option in that case.

The other idea would be to use a small(?) relay with coil directly made for line voltage. But regarding the wasted power, it would be not so good one.

Ioannis

[dhouston]

Here is a schematic.

[Dave]

I would use a single led opto rather than a dual and put a 1N4004 diode and appropriate resistor in series with it.