Metal Detector

  
Using an oscillator running at 455 kHz, the metal-detector circuit produces an indication on the meter Ml. When the oscillat
Metal Detector - schematic

or frequency changes because of metal in the field of Ll, the change will show as an increase or decrease in frequency, which produces a charge in the meter reading. The ceramic filter FILT1 produces a selective bandpass that yields this effect. Ll can be a 4` diameter coil wound on a suitable plastic form. About 10 turns of #26 wire are required. Use a frequency counter to adjust Ll and verify that Ql is operating on or near 455 kHz.



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