Metal detector 7

That metal detector circuit uses LC single-tube oscillator circuit, it is shown as Figure 8-73. In the circuit, V is oscillating tube, L is the detection coil, Cl is the resonant capacitor. After turning on power switch S, the LC single-tube oscillator circuit starts oscillation, semiconductor superheterodyne radio speaker will issue the sounds with the frequency in lkHz.
Metal detector 7 - schematic

When the search coil L detects underground metal, the radio frequency of the sound of the speaker becomes high. Component`s selection R uses variable resistor (270P seal simply connected); C2 and C3 use high frequency ceramic capacitor or glaze capacitors. V selects 3AGl or 3AGIl High Frequency Low Power PNP germanium transistors. GB uses 9V laminated battery. L uses enameled wire with †O · 5lmm which is winded on the 5mmxlOmmx8Omm magnet bar with 80 turns (60 turns at the tap, W1 has 60 turns, W2 has 20 turns. ) For increasing the sensitivity of L, it can also be winded the coil with the diameter in 3Ocm, the coil should be parallel to the ground.

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