Double coil metal detector circuit

This double coil metal detector by detecting head, transmitters, receivers, timer and audio generator, as shown in the figure a.

The metal detector is used to launch the coil and the receiving coil mutual induction coupling principle, when the coil is close to the metal body due to coupling parameters change, the oscillation frequency changes, given the high frequency audio signals.

　　

　　

　　

Figure b is the transmitter circuits.

IC1 and R1, R2, C2 composition multivibrator, f = 1.44/(R1 + 2R2) about C2, 100Hz. Ic2 and R4 and C4 composition trigger timing circuits, each time a pulse by IC1 to trigger the scheduled time, td1 = 1.1R4C4 about 165us. At the scheduled time, enabling conducting VT1 and VT2 saturated.

　　

　　

　　

Figure e-timing circuit.

IC3 and R10, C7 composition MONOSTABLE delay circuit, the delay time td1 = 1.1R10C7, 36us; output the IC3 C8, R11 differential delay triggering IC4, after td2 = 1.1R12C9, about 50us, its output is sent to the receiver, the VT3 gate opening.

　　

　　

　　

Figure c receiver circuit.

IC5 adopts uA709CP, it will loop induction signal difference zoom in, zoom in on the signal in the timing circuit to open the gate to get through the VT3 during detection amplifier IC6.

　　

　　

　　

Figure d-sound generator.

555 and VT4, R26, R27, C17 composition multivibrator. When there is no metal induction signal, VT4 cut-off. When the search coils gradually to the metal body close to the sensor signal gets bigger, the better case VT4 breakover, thus the oscillation frequency IC9 gradually increase, when close to the metal body, will issue a high frequency sound, said here have metal objects.