Or you can detect the electric field from the cable for voltage detection. Wrap 10-20 turns of hookup wire around the cable (or fit a conductive sleeve etc.). This will have capacitive coupling to the live conductor as well as the neutral (and earth conductors if fitted). So you have a capacitive voltage divider. The capacitance isn't much (100pf or so ?), but the input impedance to the pic pin can be pretty high also. I've had the setup working with a protection diode to + and grnd and feeding a ADC input on an atmel micro. Take 10 or so samples over a AC cycle and the difference between connected and not connected can be easily detected. (I think I measured the difference between the max & min of the sampled data with the input biased to midpoint using high value resistors). You do need a ground reference for you detector however - unlike the magnetic/currrent detection systems. And it won't work on neutral screened cables, but that's an unlikely requirement. RP On 11/05/07, alan smith wrote: > To answer some of the questions...this is remote with a PIC and an RF link. PIC detects the event and transmits via the RF link to mother an tattles. So video is out of the question, or a pilot light. It has to detect and report. > > Optical maybe, but may be in a dark enviroment to begin with and can't depend on the plug > size to block. > > Torroid or inductor...same issues I am thinking with the hall sensor. Difficult to the measurment sensitivity over the range. > > And, as far as something plugged in and not on...not the case. Whenever a device is plugged in, it will be on, yet may not be pulling very much current. > > Mechanical may be the best. If I could find a AC recpeticle that the blades touched when the device is unplugged, and opens when the device plugs in. > > > > --------------------------------- > Ahhh...imagining that irresistible "new car" smell? > Check outnew cars at Yahoo! Autos. > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist