Output signal is determined by supply current changes. Independent of supply voltage, this current is high or low according to the presence or the absence of a close metallic object. This metal detector circuit use two LEDs , which offer an visual indication of presence or absence at a metals ,around the coil . To adjust the circuit you need to make sure there is no metal near the coil and then set the fine adjustment to a "Mid position". After that you need to adjust the course adjustment to turn on the LED and , adjust the fine adjustment to turn off the LED.
This detector electronic circuit operates over a wide range input voltage of 4 -35 volts .? If you want you can use other values for the Cx capacitor and for L1 inductor? ( changing this value will affect the frequency oscillation and the detection range ) .
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