One of the simplest devices is flush detector shown in Fig. 1. The resistor R 1 is needed to protect the chip K561LA7 overvoltage static electricity, but, as experience has shown, it can not put. Antenna is a piece of ordinary copper wire of any thickness. The main thing is that it does not sag under its own weight, ie, It was tough enough. The length of the antenna determines the sensitivity of the device. The optimum is the amount of 5 ... 15 cm. When approaching the antenna wiring to the detector emits a characteristic crack.
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