DIYer RazorG illustrates how to make a cheap metal detector using an old AM radio, tape, and a calculator. Tune your AM radio with the volume on maximum onto the high end of the frequency but not directly on a broadcast station. Once you can hear the static from the AM radio, position the radio and the calculator (turned on) close together until you hear a loud tone. Then, tape the units together securely. You now have a working metal detector which you can experiment with by putting it near silverware or another piece of metal. This works, RazorG says, because the loud tone that comes from the radio is the calculator's electronic circuit board, which produces a radio frequency signal. The radio waves from the calculator bounce off the spoon and are heard on the radio's speakers.
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