I thought these had gone away, Fat Quarters is defunct as is the Speake & C= o site, but I just found this site which has the latest version: https://www.fgsensors.com/ The output is a square(ish) wave which varies in frequency according to fie= ld strength. Years ago I was detecting and classifying vehicles at 20 meters or so with = the FGM-1 sensors. Just FYI -- David VanHorn Lead Hardware Engineer Backcountry Access, Inc. 2820 Wilderness Pl, Unit H Boulder, CO 80301 USA phone: 303-417-1345 x110 email: david.vanhorn@backcountryaccess.com --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .