상황
A hobbyist needs a readable BFO metal detector schematic that clearly separates power, oscillator, mixer, comparator, and indicator stages.
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01
Use two BF422 Colpitts-style oscillators (search and reference) to produce a beat note.
02
Use a 7805 regulator to derive a stable 5 V rail from a 12 V battery.
03
Use an LM339 comparator to square up the detected envelope.
Reuse when building or documenting a classic BFO metal detector and you need a clean, auto-routed netlist rather than a positional wiring diagram.