Simple Metal Detector Circuit Using 555 Timer

In this tutorial, I will show you how to make a simple metal detector circuit using fewer components which is a very essential device that is used for checking persons, luggage, or bags in airports/shopping malls, hotels, etc to ensure that the particular person is not carrying any metals like guns, bombs or any other metallic types of equipment. There are different types of metal detectors like handheld, walkthrough, and ground searching metal detectors. Metal detectors can be created easily using a coil which is the main part of the device. In this project, we are going to make a simple ground search metal detector using a 555 timer IC.

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Project

Circuit Diagram

Components Required

• 555 Timer IC
• 47 KΩ Resistor
• 2.2 µF/25V Electrolytic Capacitor
• 10 uF/25V Electrolytic Capacitor
• Buzzer
• 170 Turns of 10 cm diameter coil
• 9V Battery

Circuit Connection

The circuit diagram shows all the connections of the metal detector circuit. The 555 timer IC here is used to create a square wave frequency and it generates pulses with frequencies audible to a human. The capacitor between pin 2 and pin 1 is 2.2 uF/25V which generates the audible frequency.

In the circuit, we can see an RLC circuit formed by 47 KΩ resistors, 2.2 µF/25V capacitors, and an inductor which is formed by 150 turns of copper coil. This RLC circuit is the main part of this metal detector device.

There is a small 10 uF/25V capacitor connected between the output pin 3 and the junction of the RLC circuit and its anode part is connected with a small buzzer which formed the output audible sound.

Working Principle of Metal Detector

Here the coil of the inductor is air-cored, so when a metal thing is kept near the coil, the metal thing acts as a core for the air-cored inductor. Then the inductance of the coil changes considerably. With these sudden changes in the inductance of the coil the overall reactance or impedance of the RLC circuit changes by amount when compared with the metal thing. 

At first, when there is no metal thing, the signal from the device causes an audible sound. Now with the reactance change around the RLC circuit, the signal sent to the buzzer will not be the same as it is in the first one. 

Therefore, while a metal thing is kept near the coil, the impedance of the RLC circuit changes, meanwhile the signal to the buzzer will also change with a variation.

Application of Metal Detector

This simple Metal Detector device can be used to identify metals like iron, gold, silver, etc. 

It can be used as a security system to detect any kind of illegal weapons or metallic weapons carried by anyone in malls, airports, banks, etc.