Supply voltage: 3-5V
Dimensions: 66 x 61MM
Maximum measure range: 5CM (Best measure range: 1 CM - 2 CM)
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 measure 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 measure 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 measure coil underneath the metal object.
If you need longer measure range and higher sensitivity, please create their own search coil, search coil diameter of the larger suppliers will be farther away from the probe
1 x DIY Metal Measure Kit