Simple Metal Detector Circuit Diagram

[Mood Phaneuf]

Metaldetector is a very common device that is used for checking persons, luggage or bags in shopping malls, hotels, cinema halls, etc. to ensure that person is not carrying any metals or illegal things like guns, bombs etc. Metal Detectors detect the presence of metals.

There are different types of metal detectors like hand held metal detectors, walk through metal detectors and ground search metal detectors. Metal detectors can be created easily and the circuit for a basic metal detector is not that complex.

TDA0161 Proximity Detector IC: TDA0161 is a Proximity Detector IC manufactured by STMicroelectronics. It can be used detect metal objects by detecting the slight changes in the high frequency Eddy current losses.

The TDA0161 IC acts as an oscillator with the help of externally tuned circuit. The changes in supply current will determine the output signal i.e. current is high when a metal object is near and it is low when there is no metal object.

There are three main parts in the metal detector circuit: the LC Circuit, the Proximity Sensor , output LED and the Buzzer. The coil and the capacitor C1, which are connected in parallel, will form the LC circuit.

LC Circuit: LC circuit has inductor and capacitor connected in parallel.This circuit sarts resonating when there is same frequency material near to it. The LC circuit charges capacitor and inductor alternatively.When the capacitor is charged fully ,charge is applied to inductor.

Inductor starts charging and when charge across the capacitor is nil, it draws charge from the inducutor in reverse polarity. Then inductor charge is reduced and again the process repeats.Note inductor is a magnetic field storage device and capacitor is electric field storage device.

Proximity Sensor: The proximity sensor can detect the objects with out any physical interference. The proximity sensor will work same as infrared sensor, proximity also release a signal, it will not give output unless and until there is no change in the reflected back signal.

If there is a change in signal it will detect and give the output accordingly. There are different proximity sensors for example to detect plastic material we can use capacitive type proximity and for metals we should use inductive type.

The LC Circuit, which consists of L1 (coil) and C1, is the main metal detector part of the circuit. With the help of this LC Circuit, which is also called as Tank Circuit or Tuned Circuit, the TDA0161 IC acts as an oscillator and oscillates at a particular frequency.

When the LC circuit detects 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 the coil is not near any metal object. 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 less than 1mA when there is no metal detected and it will be around 10mA (usually greater than 8mA) when coil is near to the metal.

I built it and it works pretty good. Not sensative enough to use for digging up treasures at the beach, but I think it will be useful for finding that lost bolt or screw in the grass. Next step will be building a soldered up version and mounting it on a handle. No problem finding the IC on ebay.

I have a need for similar circuit but the only difference is, the circuit I need should function the same way as this one does IN MAGNETIC FIELD. Do you know if this should function the same way under the influence of magnetic field?

A simple metal detector circuit is an electronic device that uses electromagnetic induction to detect the presence of metal objects. It is composed of a coil of wire, a battery, and a few other components that work together to create a magnetic field and detect changes in that field caused by nearby metal objects.

A simple metal detector circuit works by sending an electric current through the coil of wire, which creates a magnetic field. When the coil is near a metal object, the magnetic field is disrupted, causing an electrical signal to be sent to a speaker or other output device. The strength of the signal can indicate the size and distance of the metal object.

The main components of a simple metal detector circuit include a coil of wire, a battery, a resistor, a capacitor, a transistor, and a speaker or other output device. Some circuits may also include a potentiometer for adjusting sensitivity or a switch for turning the detector on and off.

Building a simple metal detector circuit can be a fun and educational project. You can find many online resources that provide step-by-step instructions and diagrams for various types of metal detector circuits. It is important to have basic knowledge of electronics and safety precautions before attempting to build your own circuit.

A simple metal detector circuit can be used for a variety of purposes, such as finding buried metal objects, locating lost items, or detecting metal in food or other products. It is also commonly used in security and law enforcement for detecting weapons or other dangerous objects. Additionally, metal detector circuits are used in archaeological research to locate buried artifacts.

The other day when I was searching instructables I come across on interesting and simple circuit for metal detector. It is build with 555, coil and few other components. Instructable that inspire me to do this project was this one. Main debate was: does it really work? After quick research I found this video that proof it works. That was the time when I decided to make my own metal detector.

I do believe, that before you start working on metal detector you should read more about metal detectors and how they work.

I am not hold responsible for any damage that occurred during reproduction.

The most difficult part is making coil. In great help was web calculators for air coils. With them, I calculated that with coil 90 mm width I need about 250 windings and with diameter 70 mm 290 windings that inductance can be 10 mH. You can also buy already made coils online.

I made coils core from cardboard. Coil is made from lacquered copper wire which is 0,2 mm in diameter. I did 260 turns. Before soldering, you must clean up both ends of coil. You can do that with help of sandpaper.

It's nice but the speaker turns always on.

It will be fine if the speaker turns off when there are no metal near inductor (coil)

and the speaker Turns on when a metal brought near inductor .

how can I do that?

made circuit using 2.2uf50v 10uf50v capacitors 47k resistor ne555 ic 8ohm speaker on coil i used 0.1mm enameled wire 150turns of120mm diameter . the detactor produces a high pitch sound which does not change even when coil is swept over a metal object. pliz help with specific voltages of capacitors and specific resistance of search coil

the 555 timer either sourcing or sinking a fixed amount of current from its pin 3,

so I see as the output is a fixed squarawave tone so the increasing of L coil will increase voltage on it that increasing current draining from pin 3 hence reducing tone....very simple ! I will build the circuit and examine it under oscilloscope and if there is time I will publish results here ...god willing...

in this circuit diagram pin 2 and pin 6 are connected.I think its only astable multivibrator. am i right sir ??can we design a metal detector using monostable multivibrator configuration where pin 6and pin7 are connected???

I made the exact same circuit. The coil of 170 turns, 22 gauge copper wire, 10 cm diameter and all the other components were kept the same as mentioned, but it did not work. I've tried it multiple times but not even the slightest of change in noise occurs.

Help me out. What could be the probable mistake?

Thanks for sharing this project. I was able to make a working copy with the specified components. I'm wondering if it would be possible to filter out the constant tone when no metal is near the coil by simply adding a basic RLC band stop filter between the output and the speaker. It would probably need to be a sufficiently high order one to retain the sensitivity, and band stop because both higher and lower frequencies should be able to pass (to detect both ferromagnetic e.g. iron and non-ferromagnetic e.g. aluminium). Please comment if you have tried something like this :) Also would be interested if someone had experimented with differently shaped coils (for example '8'-shaped) to improve the detection range.

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Remember this: almost all circuits (up to about 4 - 6 transistors) have the same capability: detecting a 20mm coin at about 100mm. It doesn't matter if the circuit is simple or complex, The sensitivity revolves around the circuit driving the coil. Some circuits are more sensitive to "interference" and we have demonstrated this in Circuits 1 - 8 at the end of the page. The most-sensitive circuit is a 100mm dia coil with just 12 to 20 turns and operates at about 200kHz as shown in circuit 8. The frequency of the circuit will change by one Hertz and this can be detected on an AM radio. You cannot get better than this.

The simplest circuit is shown below:Another Simple Metal Detector Circuit

To learn more about the basics of circuit-design and recognise components, component-values, go to our: Basics Electronics 1A

We also have two Metal Detector Projects:

Metal Detector MkI

Metal Detector MkII

BASIC CIRCUITRY of

METAL DETECTION

byCharles D. Rakes

Note by Colin Mitchell: The first part of this discussion is a very old article using US imperial measurements, by Charles D. Rakes. A table of wire gauges is provided at the end of the article. The rest of the circuits are from different sources.

All these circuits have about the same sensitivity as the single transistor circuit shown in fig 7 of Part II (shown below), using an AM radio as the receiver. They have been included to show the ingenuity of design-engineers, in an attempt to improve the performance.

Here is a reference from another website with exactly the same views as myself:

The Beat-frequency oscillator (BFO) is the simplest (and oldest) type of metal detector technology and is a good starting point for learning how metal detectors work. The basic beat-frequency metal detector employs two radio frequency oscillators which are tuned near the same frequency. The first is called the search oscillator and the other is called the reference oscillator.

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