Proximity Detectors

Metal Detector Circuit

A metal detector is a widely used device employed for inspecting individuals, bags, or luggage at locations such as shopping malls, hotels, and cinemas to ensure that they are not carrying any metal objects or prohibited items like firearms or explosives. Metal detectors are designed to identify the presence of metals.

There exist various types of metal detectors, including handheld metal detectors, walkthrough metal detectors, and ground search metal detectors. Constructing a basic metal detector circuit is not overly intricate, and it can be accomplished with ease.

In this project, we have developed a straightforward do-it-yourself (DIY) metal detector circuit using readily available components. This circuit can be utilized in our homes and gardens.


  • Circuit Diagram
  • Components Required
  • Component Description
  • Metal Detector Circuit Explanation
  • Block Diagram of Metal Detector
  • Working
  • Advantages
  • Disadvantages
  • Applications

Circuit Diagram

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

Metal Detector

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, a Proximity Detector Integrated Circuit produced by STMicroelectronics, serves the purpose of detecting metal objects by discerning minute variations in high-frequency Eddy current losses.

The TDA0161 IC functions as an oscillator when coupled with an externally tuned circuit. The output signal relies on changes in the supply current: it registers as high when a metal object is in proximity and low when none is detected.

The TDA0161 Proximity Detector IC is furnished with 8 pins and is available in a Dual in-line Package (DIP). Refer to the provided image for the pin configuration of the TDA0161 IC.

As per STMicroelectronics, the TDA0161 Proximity Detector IC is no longer in production. If it is still accessible in the market, feel free to embark on this intriguing project. In the event that it is unavailable, seek out a compatible IC. Should a comparable IC become accessible, we will strive to provide an update. Please share any information regarding the availability of Proximity Detector ICs in the comments section.

For this project, a 30 AWG copper wire was employed to craft the coil (inductor). The coil is wound around a reference with a 5.8cm diameter, resulting in approximately 140-150 turns in the coil.

Metal Detector Circuit Explanation

  • When any metal that is close to the LC circuit, L1 and C1, receives a resonant frequency, an electric field is formed, which induces current in the coil and affects the signal flow through the coil.
  • To make the proximity sensor value equivalent to the LC circuit, a variable resistor is needed. It is best to check the value while the coil is not close to the metal. The LC circuit will have changed signal when the metal is identified. The modified signal is sent to the proximity detector (TDA 0161), which detects the change and responds appropriately. When no metal is detected, the proximity sensor’s output is 1mA, and when metal is found, it is about
  • 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

The metal detector circuit comprises three primary components: the LC Circuit, the Proximity Sensor (TDA0161), and the output LED with a Buzzer. The LC circuit is formed by the coil and capacitor C1, connected in parallel.

When the LC circuit detects any metal, it triggers the Proximity Sensor (TDA0161). Subsequently, the Proximity Sensor activates the LED and generates an alarm through the buzzer.

Within the LC circuit, the inductor and capacitor are arranged in parallel. When an object with the same frequency approaches this circuit, it begins to resonate. The LC circuit alternates between charging the capacitor and inductor. Charge is applied to the inductor when the capacitor reaches full charge.

The inductor initiates charging, and when the charge across the capacitor reaches zero, it reverses polarity, discharging the inductor. This lowers the inductor’s charge, and the cycle repeats. It’s important to note that an inductor stores magnetic fields, while a capacitor stores electric fields.

Regarding the Proximity Sensor, it has the capability to detect objects without physical contact. It operates similarly to an infrared sensor, emitting a signal that remains inactive until there is a change in the reflected signal.

If a signal change is detected, the Proximity Sensor responds accordingly. Different types of proximity sensors are available, such as capacitive proximity sensors for detecting non-metallic materials and inductive proximity sensors for detecting metals.


The core component of the circuit responsible for metal detection is the LC Circuit, composed of the coil L1 and capacitor C1. The TDA0161 IC assumes the role of an oscillator, operating in conjunction with this LC Circuit, often referred to as a Tank Circuit or Tuned Circuit, oscillating at a specific frequency.

When the LC circuit senses a resonant frequency emitted by a nearby metal object, it generates an electric field, inducing current flow through the coil, resulting in alterations in the signal flow.

The proximity sensor’s sensitivity is adjusted through a variable resistor within the LC circuit, and it is advisable to calibrate this setting when the coil is not in proximity to any metal object. The LC circuit becomes active once it detects the presence of metal.


  • 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.


  • 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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