NE555 metal detector

In this blog we are going to discuss an application of 555 ic which is simple metal. The circuit also uses A- stable mode of IC 555 also coil and Buzzer for the indication and alert. So, let’s take a look.

First we should understand concept of inductor circuits. Inductors are coils of insulated copper wire which is also used in winding of induction motors. In all of those parameters we are basically interested in core on the inductor as depending on the core, inductance value changes drastically.

When inductor coil is wound on ferrite core like iron rod, the inductance coil inductance increases. The inductance value changes the value of reactance or impedance changes when a metal piece comes near.

Components Required:

The figure shows the circuit diagram of metal detector. The 555 IC timer is used to generate a square wave and it generate pulses with frequencies audible to human. The capacitor between pin2 and pin1 is of 2.2uf.

Here is an RLC circuit of 47K resistor, 2.2µF capacitor, and 50turn inductor. This RLC circuit is the metal detection part..

Remember the coil wound here has no core so when a metal piece comes near the coil, the metal piece acts as a core. By this metal , the inductance of the coil changes or increases considerably. With this sudden increase in inductance of coil the overall reactance or impedance of the RLC circuit changes by a considerable amount when compared without the metal piece.

This makes the sound of piezo buzzer changed and it is hearable when happens. This sound change can be taken as detection of metal presence for the system.