Detecting 240V with a PIC (Part2)

[Darrel Taylor]

The Opto you're using has a Triac type output, which is meant to switch AC voltages.

You need one with a Transistor output, could be either NPN or PNP, but NPN is more common. Then with a pull-up resistor on the collector and the emitter to ground ... it should work.

[The Master]

Good idea thanks!

I found some transister ones in rapid. Some even have AC input so i can drop the diodes and they are cheaper anyway. They dont seem to have any datasheets so ill request those tomorrow and maybe buy a few of each type.

Thanks for your help

[Melanie]

Do a search for a K1010 (available from RS). Put a 1N4007 across it (in reverse to clamp the negative cycle because the reverse voltage will almost certainly exceed the opto's max rating and you're in danger of blowing it up). Feed that with a 270K Resistor (mains rated... the CR25 types are marginal here - unless you use say 2 x 150K - one in each input leg). Use a PIC pin with a pull-up (internal weak pull-ups are just fine) and set your software to detect the 50/60Hz AC pulses (no pulses - no mains).

PS... just in case anyone reading this is in a part of the world where they have toy voltages coming out of the wall, the above is good for 220-240vAC.