555 double coil metal detectors

As shown in the following figure is double coil metal detector circuit. The probe by the probe, a transmitter, a receiver, a timer and sound transmitters and other components.
555 double coil metal detectors - schematic

Transmitter circuit shown in (b), by the multivibrator (IC1, R1, R2, C2), single stabilizer (IC2, R4, C4) composition, and the timer IC2 by multivibrator IC1 output pulse trigger. Oscillation frequency of f 1.44/(R1 + 2R2) C2, the corresponding icon parameter is about 100Hz. Timer in time td l.1R4C4, icon parameter corresponding to approximately 165 mu s. In the timing, (high) signal from the output enable pin IC2 BG1, BG2 saturated conduction. Receiving circuit shown in (c), mainly by the differential amplifier and the detector amplifier. Tibetan differential amplifier IC5 ( mu A709CP) the sensor signal diagram (b) of the coil differential amplification, the amplified signal during the open gates of a timing circuit through BG3, to the sense amplifier IC6. A timing circuit shown in Figure (d) shown by the two monostable delay circuit IC3, R10, C7 and IC4, R12, C9 composition than, IC3 and IC4 by the output control. Wherein the delay time of the former is td l.1R12C9, icon parameter corresponding to about 36 mu s; the latter hope to delay time td2 1.1R10C7, icon parameter corresponding to about 50 mu s, the output signal supplied to receiver BG3, as open gates. Sound generator as shown in (e), the core is composed of 555 (IC9), BG4, R26, R27, C17 and other multivibrator composed. When the metal-free sensor signal from the signal output enable pin IC6 BG4 off multivibrator does not work, corresponding speaker does not sound. When metal sensing signal, and gradually close to the search coil metal body, the sensor signal becomes large, BG4 conduction situation changed for the better, so that the oscillation frequency IC9 gradually increased, when close to the metal body, high output by the IC9 oscillation frequency signal drives the speaker issued a high-frequency sound, it indicates there is a metal object.

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