Metal Detector Circuit

Metal detector 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.

In this project, we have designed a simple DIY type Metal Detector Circuit using very simple components that can be used in our homes and gardens.

Metal Detector Circuit Image 1
Metal Detector Circuit Image 2
Metal Detector Circuit Image 3
Metal Detector Circuit Image 4

Circuit Diagram

The following image shows the circuit diagram for the metal detector circuit.

Metal Detector Circuit Diagram

Components Required

  • 1 x TDA0161 Proximity Detector IC
  • 2 x 47nF Capacitors (Ceramic Capacitor code 473)
  • 1 x 1 KΩ Resistor (1/4 Watt)
  • 1 x 330 Ω Resistor (1/4 Watt)
  • 1 x 100 Ω Resistor (1/4 Watt)
  • 1 x 5 KΩ Potentiometer
  • 1 x 2N2222A (NPN Transistor)
  • 1 x 5V Buzzer
  • Coil (copper wire of 26 – 30 AWG is taken and it is wound in to a coil of diamater 5 – 6 cm and 140 – 150 turns)
  • Additional Components (for LED)
    • 1 x 220 Ω Resistor (1/4 Watt)
    • 1 x 5mm LED

Component Description

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.

TDA0161 has 8 pins and it comes in Dual in – line Package (DIP). The following image shows the pin diagram of TDA0161 IC.

NOTE: According to STMicroelectronics, TDA0161 Proximity Detector IC is obsolete. If it is available in the market, go ahead and make this fun project. If it isn’t available, try to find a replacement IC. We will try to update if any similar IC is available. If you find any Proximity Detector ICs, please mention it in the comments section.

Coil (Inductor): We have taken a 30 AWG Copper wire for this project. It is then wound in to a coil using a 5.8cm diamater reference. The coil consists of 140 – 150 turns.

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 coil is near to the metal
  • When the output pin is high the resistor R3 will provide positive voltage to transistor Q1. Q1 will be turned on and led will glow and buzzer will give the buzz. Resistor r2 is used to limit the current flow.

Block Diagram of Metal Detector

block diagram

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.

Proximity sensor(TDA0161), is triggered by this LC cirucit if any metal is detected.The Proximity sensor will then turn on the led and produces alarm using buzzer.

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.

Working

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.

When the output pin is high, the resistor R3 will provide positive voltage to transistor Q1. Q1 will be turned on and LED will glow (not shown in the circuit) and buzzer will be activated.

Advantages

  • 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.

Disadvantages

  • 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.

Applications

  • This simple Metal Detector can be used to identify metals like iron, gold, silver etc.
  • Since it is a simple project, we can use this in our home to scan for nails, metal scraps etc. which are not easily spotable by naked eye.

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56 Responses

    1. TDA0161-Proximity sensor
      Inductor- 680PF
      Transistor- 2N3904
      R1,R4,R5-1k;R2-330,R3-120.
      RV1-10k
      Capacitor-0.047uf-(Quantity-2)
      Buzzer
      Battery
      Led

        1. please can you share the alternative components of the TDA0161 Proximity sensor with me. Am talking about the metal detector circuit

  1. please I want a brief notes about the functionality of the project and also how to give a justification of the project

  2. Can we simulate this on Proteus or Multisim?
    If yes, then after completing the circuit how am i supposed to show the presence of the metal ?

  3. TDA0161 Proximity Detector IC not available in market plz help me .and available IC in market plz contact send me

  4. Hi , the project is very good . I just have 2 doubts :
    1- If i want to increase the range of the metal detection how do i do that .
    2- What is the other alternative to copper wire used .

  5. Am trying to come up with a project of this kind but i’ve not found TDA0161 in the market and even its substitute which CS209/CS209 IC is not in the market too. please someone assist me get one piece of this tda0161. thank you

  6. Dear sir

    I increase range up to 10 meter than i what nead to changing circuit. plz tell me about

  7. there are two pins connected on VR1, is the 3rd pin left open as shown in the diagram, or is it meant to be grounded.

    Pin 8 is also left open on the TDA chip, should this be similarly grounded too.

    Thanks.

    1. 3rd Pin of VR1 is left open.

      Coming to Pin 8 of TDA0161, usually a 0.001µF (1nF) capacitor is connected between Pin 8 and the output pin (Pin 6). But it can be left floating (as per the datasheet by ST Microelectronics).

  8. 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.

  9. I have this circuit built but I am not sure its working correctly. No matter what I do the buzzer turns on as soon as I power up. Any suggestions?

  10. Hello there,

    Nice and easy circuit.

    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?

    Thanks,

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