I was a youngster, my father (and I) built what must have been the simplest BFO metal detector at the time -- designed I think by the famous Frank Rayer. The first time we used it, we found a wristwatch. The metal detector used several components, a carefully wound coil -- and a MW radio to provide the beat frequency. Here is my first (the world's first) one-component BFO design -- or two, if one includes the coil. It uses a CMOS 4001 quad NOR gate IC. There is a suitable coil at BFO Metal Detector . Wire the Faraday shield to the battery negative (the switch side is positive). Or use a general purpose 100µH radial inductor to create a pipe-finder instead. A lead from IC1d pin 11 is attached to a MW or SW radio aerial, or wrapped around the radio. Then tune in, and experiment. OBSERVATION: Don't expect much from this one -- but then again, it is so very simple to make. Note that IC1 is sensitive to static. One could use a turned-pin DIL socket to avoid damage -- turned-pin because this is a high frequency circuit. The IC pinout will be found on the Internet.