Before Carl Moreland was Engineering Manager at White's Electronics (and now First Texas), he created a website that has more technical information on metal detectors than any I know of. The Geotech website has lots of interesting stuff and in particular it has a lot of "build your own" metal detector projects for the electronically minded. I have never done this myself but if you were ever curious about what makes detectors tick a lot can be learned here. Projects http://www.geotech1.com/c