This circuit, from a 1978 publication, emits a modulated signal when the fine sensor is interrupted. With a coil formed by 20 turns and 50 + 50 turns of wire 28 or 30 in a ferrite rod, the signal will be in the range of medium waves. The other transformer is a driver obtained from a transistorized radio or recorder of that time. The antenna must be 80 to 120 cm and the transistors can be BC558 with the emitter connected to the positive power line. The circuit must also operate on 6 V power.
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