Detect 240V with a PIC

[The Master]

Hi, Ive got some new smoke machines for halloween and the buttons use 240V. Ive got the control part sorted. Im using triacs. The light also runs on 240V. Is it possible to connect that into a PIC chip somehow so the PC can detect when the smoke machine is ready? I know it would be pretty stupid to connect it directly. I have some opto isolators that i use for controlling the triacs. Could i use a resistor and connect the 240V into the opto isolator?

[dhouston]

Most PIC pins have clamping diodes so (assuming you are using a pin with these diodes) you can connect it directly using a 10M resistor to limit the current.

[The Master]

Thats good. I need to order some more stuff from Rapid soon so ill add some of those resistors to the order. As its 240V i think i will still use an isolator just to be on the safe side.

Thanx

[dhouston]

In that case you won't need 10M resistors. Here's a circuit you can modify for your app...

• http://www.edn.com/index.asp?layout=...leid=CA6466210

[skimask]

http://www.edn.com/index.asp?layout=...leid=CA6466210[/list]

Look at the LEDs on page 77 of that document
Must've been an off day for the editors...

[The Master]

The circuit diagram in the PDF looks good. Nice and simple.

How do i know what value resistors to use? Do i stick with 130K as shown in the diagram? I would have thought it varies for each type of optoisolator. I tried to calculate it based on the maths from a site macrakit linked to Designing LED lighting. I worked out that for my opto isolator the resistors should be 3K975. I think ive gone wrong somewhere because i wouldnt have thought it would vary that much. Im using a MOC3020M.

I take it the diode is just to stop reverse voltage going into the optoisolator. Would it work the same if it was in series with it?

I think im missing some of the document. skimask mentioned page 77 but all i see is a single page with a short writeup and a link to a PDF file. I dont see any kind of navigation for multiple pages either