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20-11-2017, 01:06 PM

Hi, I got a VK 557 metal detector and did the connections as specified, but as soon as the battery is connect the LED glows and the buzzer starts buzzing, not stopping even if there is no metal neary by and there is no differnce in buzzer sound if I try to keep a metal object. Please help.
Thanks,
Jayapriya

jaseela123d · 20-11-2017, 02:50 PM

[Image: metal_detector.png?resize=300%2C140]

This circuit is more useful for security checking. The metal detectors available in the market are quite expensive. This metal detector can be used to detect metallic objects of slightly larger size and used a detection coil. This coil should be kept close to metallic objects for detection. The entrance to Circuit is an R.F. Oscillator range. The sensing coil forms parts of the tuned oscillator.

When the coil approaches a metallic object, magnetic energy is observed and the oscillator does not work. Then, the final transistor drives and the buzzer is activated. Use a 9-volt battery. After connecting the battery, adjust the 4.7k preset until the circuit stops ringing.

LIST OF PARTS:-

RESISTANCE

• R1, R4 - 56K

• R2 - 3K3

• R3 - 22K

• R5 - 2K7

• R6 - 2K2

• R7, R9 - 680E

• R8 - 15K

• P1 - 5K 3386 Trim

CONDENSERS

• C1, C6 - .1PF (104) 100 KPF

• C2 - 1KPF (102) .001PF

• C3 - 220PF

• C4 - 270PF / 100V

• C5 - 12KPF / 100V (.012 / 25V)

• C7 - 100 / 25V

TRANSISTORS

• Q1,2,3,4 - BC 547 PH

DIODE

• D1,2,3,4 - EN 4148

MISCELLANEOUS

• LED1 - 5MM red LED

• COIL1 - Metal detector coil

• Buzzer - VK 27 CT (S)

• Supply - Snapper 9v

• PCB - PCB VK 557

20-11-2017, 03:45 PM

Thanks, but please help me with how to tune the oscillator.

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