Metal Detector Using Arduino

Metal detector is a device used to detect the presence of a metal in its proximity without touching it. This project explains the concept of detecting the presence of a metal using the method of inductive sensing. The basic concept used is that the presence of a metal can vary the inductance value of an inductor. The prototype discussed here is a modified version of an inductance meter, which has the ability of sensing the change in inductance and triggers an output.

The inductance meter is a device that can be used to measure the unknown inductance of an inductor or a simple coil. The project makes use of a tank circuit, in which there will be a capacitor and an inductor connected in parallel. The natural resonating frequency of the tank circuit varies with the presence of a metal in its proximity.The prototype has been developed using an easy prototyping platform, Arduino board. The prototype is built on a breadboard in which there is an inductor placed and any metal brought near to that inductor will trigger an alarm through a loudspeaker. 

DESCRIPTION:

The Arduino based metal detector explained in this project is basically a frequency meter which measures the resonating frequency or time period of a tank circuit. The resonating frequency of a tank circuit is fixed however the presence of metals can vary it slightly. The tank circuit is a general term representing an inductor and a capacitor connected in parallel. This circuit is also called parallel LC circuit, in which the ‘L’ denotes the inductance and the ‘C’ denotes the capacitor.This tank circuit is made to oscillate at its resonating frequency by suddenly discharging it after a period of constant charging. Once started discharging the tank circuit will produce a type of oscillation is called ‘Damped oscillation’

The above image is the representation of a damped oscillation happening at the output of a LC tank circuit. The frequency of the oscillation is related to the value of the inductor ‘L’ and the capacitor ‘C’ in the circuit and is given by the following equation.

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