I'll have to look at this and see if it might work. Some of the other ideas....dont really fit because of the application....details would make sense of it all...but I am under NDA so can't divulge more than the generics. Suffice to say....the devices under "watch" are not under the control of the client.....yes I know, that raises more questions but...if its outside the box and plug, there is no control. It all has to be inside behind the plate. Thanks to all for the suggestions, thats what I like about this group..very diverse populace with lots of good ideas. "Peter P." wrote: Mike Harrison whitewing.co.uk> writes: > As it's AC, a simple capacitive charge pump would give enough voltage to > drive a LED or optoisolator. Actually, no, because it would require Germanium diodes and would still provide too little current for an opto. The easy way to sense it was as I said, using a 1:1 (can be other ratio) pulse transformer capacitively coupled. For ordinary diodes something like this should work: +---C0---+ | | A o----+-A-D1-K-+----o | | +-K-D2-A-+ | | C1 R1 | | +-A-D3-K-+ | | +K-LED-A-+ With LED=ir (optocoupler, Vf=1V), D3-Schottky, C1=10uF and R1=5R. C0=0.1uF, D1+D2 = 1N4001 etc Peter P. -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist --------------------------------- Looking for a deal? Find great prices on flights and hotels with Yahoo! FareChase. -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist