From: "Colin Constant" I'm just wondering if there's a way to measure the speed of an electric motor > (Dremel tool) by looking at the noise it inflicts on the line (if, indeed, it > does). > You can make a speed sensor which needs no connection to the motor. Just look at the noise e.g. pitch. Not too inaccurate as long as doppler effects are minimal. If doppler shift is occuring, you're probably swinging a switched on dremel round your head so innaccuracy is the last of your worries!! Personally I'd prefer this option over a "noise" measuring device. I feel it would pretty difficult get "just enough" noise to trigger the circuit without completely swamping it.... Ben -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.