Features:
Supply voltage: 3-5V
Dimensions: 66 x 61mm
Maximum detection range: 5CM (Best detection range: 1 CM - 2 CM)

Principle explanation: Q1, L1, L2, C2, C3, R1, W composed of high-frequency oscillation circuit, adjustment potentiometer W, you can change the oscillation stage gain, the oscillator oscillating in a critical state, that is just the oscillator start-up. Q2, Q3 when the composition of the detection circuit, the circuit normally oscillate voltage AC voltage exceeds 0.6V, Q2 will be in the negative half cycle of conducting the C4 discharge short circuit, resulting in Q3 ends; when it detects metal objects near the coil L1, will be metal conductor eddy current is generated, the oscillation circuit of the energy loss increases, positive feedback weakened in the critical state of the oscillator weakened, if not impossible to maintain the minimum required energy oscillations and to stop, so Q2 is turned off, R2 to C4 charge, Q3 is turned on, pushing the buzzer sounds. According to whether the sound, you can determine whether the detection coil underneath the metal object.

Note: If you need longer detection than 5CM range and higher sensitivity, please create their own search coil, search coil diameter of the larger suppliers will be farther away from the probe
Kits parameters:
 
Supply voltage: 3-5V;
Dimensions: 66 * 61MM;
Maximum detection range: 5CM;
The new board simple metal detector kit with 1.6mm double-sided fiberglass board do
 
Package List: 
PCB board 1pcs
Buzzer 1pcs
100UF25V electrolytic capacitors 1pcs
104 ceramic capacitor 2pcs
222 polyester capacitors 2pcs
220K resistance 0.25W 1pcs
2.2K resistor 0.25W 1pcs
100 European blue potentiometer 1pcs
9018 transistor 1pcs
9015 transistor 1pcs
9012 transistor 1pcs
22AWG wire red 10CM 1pcs

Package included:
1 x DIY Metal Detector Kit (unassembled - require soldering)
Instructions/schematic are NOT included. We don't provide technical assistance please make sure that you are familiar with the product before purchasing.