Matchless Metal Detector, has had more than 100 000 views on YouTube alone (some examples on the right). I sold the copyright to that one in June 2002. A pity I didn't patent it! That design was based on a dual CMOS 555 integrated circuit. I further published a single CMOS 555 RX (receive) circuit in October 2011, the smallest that there is. That became the basis of one of the smallest self-contained metal detectors, the BB Metal Detector. OBSERVATION: It's great to see the enthusiasm and innovation in the videos. Before I finally retire from metal detector design, I still have a magnetometer in mind. It's going to be a good one -- if and when!