simple metal, which is often needed at home – for finding pipes, fittings, wires, nails, etc.. in the wall. The apparatus may also be used to search for metals, which are in the land. The only limitation is the range of – the detector reacts to objects, spaced a few centimeters from the sensor coil.
- metal detector: single, easy-to-reel manufacturing
- audible alarm the presence of metal
- Generator alarm activation – LED diode
- small number of elements, easy assembly
- power supply 9 AT (6F22 battery)
Schematic diagram of the detector shown in Figure. 1. a reference oscillator, built on NAND U2C member using a piezoceramic resonator, It operates at a frequency of about 450 kHz. A second tunable oscillator element as a coil L1 is built on the gate U2B. In equilibrium, it is set to the same frequency, and that the reference oscillator.
An additional variable capacitor C5 allows it to be calibrated. Yield measuring generator (a coil L1) connected to the input of the monostable oscillator, consisting of elements U2A C8 and R7, which runs from each edge of the signal from gate U2B. Both signals control gate U2D, the output of which, depending on the difference of the two frequencies, there is an acoustic frequency signal. He controls the converter BZ1.
System, composed of vents U1D, E, F, It is a simple flip-flop, who works as U2 power supply switch (CMOS4011). Subsequent pressing button S1 alternately turns on and off the device. Additional diode D1 indicates the activation of both generators. As used power inverter buffers CMOS4049. In the "sleep" system consumes little current of several microamperes, that does not affect the status of the battery. After turning on the power source U2 (conclusion 14 connected to the output gate U1F), the system starts to work, then the current consumption is increased to about 30 mA.
Assembly and commissioning
Scheme collected on single-sided printed circuit board. An arrangement of elements shown in Figure. 2.
Initially, you need to install Z-jumper, passive components, resistors and capacitors, necessary to use panels (seats) to IC. Then we can paste BZ1 converter PCB, do not forget to connect the wires. The final element is the airbag coil L1, that needs to be wound out 69 turns of insulated wire on the roller diameter 50 mm. The diameter of the wire is not critical condition. After that, wrap the tape reel. with the PCB coil must be prepared in such a way best applied silicone hot glue to the body, as shown in Figure. 3.
S1 button can be placed in a place, convenient for finger. The proposed body should also conform to the type of battery “crown” 9V 6F22. After the addition of the battery and pressing the S1 button on the speaker to be heard the sound or no sound (in the case of mutual vibration damping) and should light up the LED D1. Turn the trimmer capacitor C5 and simultaneously lift the metal coil L1, install the C5 axis so, to changes in the acoustic signal have been as high as possible. After this operation, the housing can be closed, the detector is ready for use. If the detector can not be adjusted, the value of the capacitor C4 in the range 150 pF … 470 pF should be reduced or increased.