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Simple Metal Detector Circuit

This article show a special trick to make a Simple Metal Detector Circuit

It uses simple circuit not like other circuits and needs only one transistor.

The circuit find metal by catching signal from a normal radio.

What is a Metal Detector:

Metal detector is electric circuit made to check if metal is close or not.

It works using electromagnetic induction when metal comes near and it changes the frequency of special circuit.

Metal detector are used in many place like factory, treasure hunting, airport security and old history digging.

Circuit Working:

Parts List:

CategoryDescriptionQuantity
Resistor1/4 W CFR
330k1
Capacitors
Ceramic 68pF1
Trimmer 500pF1
Semiconductor
Transistor 2N39041
Search Coil as given in the text1

Below we can explain how metal detector circuit work:

First take plastic round base 3 to 4 inch wide and wind wire on it 30 times and this will make coil called L1.

Connect L1 to circuit using three wires which will become search coil or sensor.

To is used for ground metal finding and fixes coil at end of long wood or plastic stick.

To find metal at inside walls keep whole circuit inside small box so we can carry easily.

The circuit work when metal come close and disturb the electromagnetic field made by coil L1.

When metal come L1s value and frequency both changes.

Use small battery radio near circuit.

The radio catches this change and make loud sound.

First tune radio to local station an we will hear beat or small flutter sound.

Now turn capacitor C1 slowly until we hear low beat or chirp which mean it is set right.

When metal is near the sound changes more and this will help find hidden metal.

Circuit find changes in field made by L1 when metal is there.

Radio make these changes louder so its easy to know metal is there.

Capacitor C1 need to adjust correct to get strong signal.

Formula:

Below formula helps to find starting frequency of metal detector circuit:

f = 1 / 2π√(L * C)

where:

How formula work:

Multiply L and C which then take square root and then multiply by 2π and do 1 divided by that number which then gives f.

If we make C or L bigger frequency f go down.

If C or L is smaller then f goes up.

This help set circuit to correct working speed. lower capacitance or inductance.

How to Build:

The following are the connections steps for building a Simple Metal Detector Circuit.

Make Oscillator Coil L1:

Connect Coil to Circuit:

Build Circuit on Breadboard:

Set Up Radio Receiver:

Power the Circuit:

Test the Circuit:

Try Metal Detecting:

Improve the Circuit:

Conclusion:

Anyone can make working Simple Metal Detector Circuit by following these above steps.

If we need for different metal finding job we can change circuit like use different capacitor values or change coil design.

References:

Design of a Beat Frequency Oscillator Metal Detector

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