The circuit consists of a tuned colpitts oscillator and a switching circuit any ferrous materials brings the resonance circuit to be untuned , this untuning is sensor by the transistor circuit to buzz a buzzer .
The value of presel resistor 4.7 k ohm has to be adjusted till the circuit stops sounding inthe absence of any ferrous materials.
sensing coil 2.547 NPN transistors
SKILL LEVEL REQUIREMENTS:
3.9 volts battery cap
5.NPN BC547 transistors
6.100 nano farad capacitors
7.100 micro farad 25 volts capacitors
8.10 k preset (pot)