Metal detector 2

  
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This metal detectors described in the example can be used to detect metal objects with high permeable magnetic substances. The working principle. The metal detector circuit is composed of the power circuit, sine wave oscillator, PLL phase-locked loop circuit and hybrid amplification circuit, it is shown in Figure 8-68. Power circuit is composed of
Metal detector 2 - schematic

the battery GBl, GB2, filter capacitor Cl, C2, and the power switch S (Sa, Sb). Sinusoidal oscillator circuit consists of transistors Vl, detecting coil L, capacitor C3-C5 and resistors Rl, R2. PLL circuit is composed of dual time-base integrated circuit and resistors R3, potentiometers RPI, capacitors C6-C8. The hybrid amplification circuit is composed of the transistors V2, V3, resistors R4-R6, potentiometer RP2 and ammeter PA. Rl-R6 use l/8W or 1/4W carbon film resistors. RPl uses multi-turn precision potentiometer; RP2 uses general lap synthetic membranes potentiometer. Cl and C2 select electrolytic capacitors with voltage in 16V; C3-C5 and C8 select monolithic capacitors; C6 and C7 select high-frequency ceramic capacitors.



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