Metal Detector Circuit

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A metal detector is an electronic device that detects the presence of metal nearby. It works by using electromagnetic fields to sense metal objects—either on or below the ground or hidden inside other materials.

Components Used:

  • 9012 Transistor *2
  • 9018 Transistor *1
  • 470 Ohm
  • 2k Ohm
  • 200k Ohm
  • Red LED *1
  • 222 Capacitor
  • 104 Capacitor
  • 100uf Capacitor
  • Buzzer
  • 3.7v Battery
  • Switch
  • Potentiometer

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The LM358 is a reliable, affordable, and versatile operational amplifier that is ideal for a wide range of analog applications. Whether you're building audio amplifiers, filters, voltage followers, or sensor signal conditioning circuits, the LM358 is a solid choice. Its ease of use, low power consumption, and dual op-amp configuration make it a go-to component for both beginners and experienced engineers. Proximity Sensor Circuit
Proximity Sensor Circuit


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Circuit Diagram:

Metal Detector Circuit
Metal Detector Circuit

9012 Transistor:

The 9012 transistor is a complementary PNP transistor to the 9014 NPN transistor. It’s used in similar low-power, general-purpose applications like switching and amplification in electronic circuits, especially in push-pull amplifier configurations when paired with the 9014.

🔍 9012 Transistor: Technical Specifications

ParameterValue
TypePNP
Collector-Emitter Voltage (Vce)-40V
Collector-Base Voltage (Vcb)-50V
Emitter-Base Voltage (Veb)-5V
Collector Current (Ic)-800 mA
Power Dissipation (Ptot)625 mW
DC Current Gain (hFE)64 – 400
Transition Frequency (fT)250 MHz
Package TypeTO-92

📦 Pin Configuration (TO-92 package)

Looking at the flat side of the TO-92 package with the pins facing down:

  1. Emitter (E) – Left
  2. Base (B) – Middle
  3. Collector (C) – Right

⚙️ Operating Regions (for PNP)

  • Cut-off (OFF): Base voltage is more positive than emitter → no current flows.
  • Active (Amplification): Base is slightly negative relative to emitter → collector current is proportional to base current.
  • Saturation (ON/Switching): Base is much more negative than emitter → maximum current flows.

🛠️ Typical Uses

Hobby electronics.

Audio amplifiers (often with 9014)

Switching small loads

Complementary circuits (push-pull stages)

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