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pebe
Nobel Prize Winner
United Kingdom
1078 Posts |
 Posted - Jul 20 2012 : 10:31:13 AM
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| The circuit is of a BFO type metal detector. The search coil, L2, and the caps with it oscillate at a certain radio frequency. T1 is part of a tuned circuit that runs at the same frequency. Both are fed to the audio stages. When the two are exactly in tune no sound is heard. When metal is brought near the search coil, the frequency of L2 is shifted. The difference in the two oscillators's frequencies then produce a beat note that you can hear. |
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Metal detector
