555 timer ic


A metal detector can be used at airports, in theatres, or elsewhere. It is used to detect someone holding a metal (arms, etc.) to protect citizens. We will develop a basic detector circuit in this project. There are so many metal detector projects, but most of them are in the design complex so we will make a basic 555 Timer IC metal detector circuit. This circuit is easy to make and requires a few basic components.

This simple circuit consists of the following parts;

  • Resistor – 3.3 k ohm – 1 nos
  • Resistor – 2.2k ohm – 1 nos
  • Resistir – 68ohm – 1 nos
  • Capacitor – 10uF/16V – 1 nos
  • Capacitor – 10pF – 1 nos
  • Capacitor – 100pF – 1 nos
  • Battery – 6V
  • NPN transistor – BC548 – 1 nos

Metal Detector Circuit Explanation

  • When the LC circuit that is L1 and C1 has got any resonating frequency from any metal which is near to it, electric field will be created which will lead to induces current in the coil and changes in the signal flow through the coil.
  • Variable resistor is used to change the proximity sensor value equal to the LC circuit, it is better to check the value when there is coil not near to the metal. When the metal is detected the LC circuit will have changed signal. The changed signal is given to the proximity detector (TDA 0161), which will detect the change in the signal and react accordingly. The output of the proximity sensor will be of 1mA when there is no metal detected and it will be around 10mA when the coil is near to the metal.
  • When the output pin is high the resistor R3 will provide a positive voltage to transistor Q1. Q1 will be turned on and led will glow and the buzzer will give the buzz. Resistor r2 is used to limit the current flow.

Applications and Uses

The metal detector is very common in shopping centers, restaurants, movie halls, and other locations to track people’s baggage or luggage, to guarantee that people should not wear metals or unlawfully explosives.


  • The Proximity Detector IC TDA0161 based Metal Detector Circuit is a very simple and easy to construct metal detector that can be used to detect small metals in our homes, offices and gardens.
  • There is need for any microcontroller as the Proximity Sensor will be sufficient to implement the project.


  • The main disadvantage of this Metal Detector Circuit is the range of detection. The metal object has to be at a distance of 10mm for the detector to detect it.

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