In message , Paul Nolan writes: >I guess your circuit just picks up the fundamental note. What happens >when you play a chord? It's probably quite hard to pick more than one >note. Hmmm, I guess a fourier transform would have to be involved and >that would probably blow the PIC capacity. Just a thought. There is a more fundamental problem, here. Whether the frequency counter is made from a PIC, vacuum-tubes, or mechanical relays salvaged from old soda machines, it will probably work on the same principle in that there will be a counting device that is stepped through its count by the incoming signal until the time base times out and the count on the counting device is needed. The time base will reset the counter and put the last count on the display and the count starts all over again until the next reset. The whole system is based on the idea that the signal is composed of a single periodic wave form. A chord would produce a more complex series of patterns that would definitely make the counter count, but the result would be worthless because the pulses did not arrive in a steady procession. Imagine an extreme case in which a counter with a 1-second time base is connected to a signal that consists of 5 pulses of a 1Mhz carrier every 10 seconds. For 9 of 10 seconds, the counter will read 0 because it saw nothing. During that tenth second, it will see the five pulses and show 5 Hertz because that's what the counter had in it when reset. The output can't even tell you if those 5 pulses were really 1us apart or 20us. Maybe the time base caught the counter just as it got a couple of the pulses such that the display reads two and then three during the next sample. It might be a bit confusing. I am sorry to have taken so much band-width, but this has been a very good discussion that has touched on some fundamental issues which come up when we want to digitally read signals and try to make sense of them. Martin McCormick WB5AGZ Stillwater, OK 36.7N97.4W in Tornado Ally OSU Center for Computing and Information Services Data Communications Group