Design, Construction and Characterisation of Metal Detector Device

Abstract

A metal detector device based on Beat Frequency Oscillator (BFO) was designed, constructed and characterized in this research work. The device comprises basically of two modules; the transmitter and receiver module. The transmitter module is a resonant inductor-capacitor (LC) circuit oscillator based on Colpitts oscillator while the receiver module comprises; tuning circuit, demodulating unit, preamplifier the amplifier and load. The receiver oscillator, turning circuit is synthesized with a tapped inductor cored with a ferrite rod and a variable capacitor of 500PF. With this configuration the receiver oscillator can be made to oscillate at close radio frequency (RF) to that of the transmitter and hence interference occurs to produce an audible note. This audible note is demodulated by the demodulator; IN 133 germanium diode and passed to the preamplifier; two matched complementary pair of transistors – C9013 and A733. LM386 OP-amp with its gain set at 200 performs the final amplification and drives directly the load; 8 0hm () speaker. When a metal object is brought near the transmitter inductor (search coil) it modulates this audible note; it will fall for ferrous metal and rise for non-ferrous metal. The device has been successfully tested and it worked.