Metal Detector

Published:2011/7/20 5:58:00 Author:Sue | Keyword: Metal, Detector | From:SeekIC

As seen in figure 8-23, the detector circuit consists of oscillator, mixer, frequency to voltage converter. It has many advantages such as high sensitivity, direct display. It can fix the position of metal and the deepest detection depth can reach 2 meters. IC1(555) and L1,D1,RP1 will compose detecting oscillator. L1 is detecting coil which will be put in the detecting handle. Its oscillate frequency f1=0.72R/L1. The parameter's corresponding frequency in the figure is 26kHz. To choose the extra long frequency of 26kHz can abate the soil's absorption of the electromagnetic wave. IC2(555) and L2,D2,R1 will compose referency oscillator. The two oscillate signals will be put on VT1 to be mixed, and then the difference frequency signal will be put on IC3. IC3 uses LM2917. It is a integrated circuit with charge pump and comparator circuit and is used as frequency to voltage converter. Its degree of linearity is usually within 0.3%. It will convert the input difference frequency into voltage which will be shown in the direct current voltmeter with a range of 3V. The load can also be replaced by audio circuit.



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