상황
A visually impaired electronics hobbyist needs a non-visual way to verify continuity between test points. This battery-powered tester produces an audible relay click when the probes touch a conductive path.
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01
Use a relay with its NC contact in series with the coil to form an electromechanical buzzer
02
Provide a 9V battery and current-limiting resistor for safe probe voltage
03
Tie the unused NO relay contact to no_connect
When a simple, robust audio-feedback continuity tester is needed without a microcontroller or piezo buzzer.