How to Use 2.1mm DC Barrel Jack: Examples, Pinouts, and Specs

The 2.1mm DC barrel jack is a widely used electrical connector designed for power supply connections in electronic devices. It features a cylindrical design with a 2.1mm inner diameter and a 5.5mm outer diameter, making it compatible with standard DC power plugs. This component is commonly used in projects requiring a reliable and secure power connection, such as Arduino-based systems, small appliances, and DIY electronics.

• Powering Arduino boards and other microcontrollers
• Supplying power to small electronic devices and modules
• DIY electronics projects requiring a detachable power source
• Prototyping circuits with external power supplies

The 2.1mm DC barrel jack is designed to handle low-voltage DC power connections. Below are its key technical details:

• Inner Diameter: 2.1mm
• Outer Diameter: 5.5mm
• Voltage Rating: Typically up to 24V DC
• Current Rating: Up to 5A (depending on the specific model)
• Mounting Style: Panel mount or PCB mount
• Polarity: Center pin positive (in most cases, verify with your power supply)
• Material: Metal contacts with plastic or metal housing

The 2.1mm DC barrel jack typically has three pins for connection. The table below describes each pin:

Note: The switch pin is not always present in all models. Check the datasheet of your specific barrel jack.

1. Mounting the Jack:

   • For panel-mount jacks, drill a hole in your enclosure to fit the jack and secure it with the provided nut.
   • For PCB-mount jacks, solder the pins to the appropriate pads on your circuit board.

2. Connecting Power:

   • Identify the polarity of your DC power supply. Most barrel jacks are center-positive, meaning the center pin is connected to the positive terminal.
   • Solder the center pin to the positive rail of your circuit and the outer sleeve to the ground rail.

3. Using the Switch Pin (if available):

   • The switch pin can be used to disconnect a battery or secondary power source when a DC plug is inserted.
   • Connect the switch pin to the secondary power source, ensuring proper polarity.

• Verify Polarity: Always confirm the polarity of your DC power supply before connecting it to the barrel jack. Reversed polarity can damage your circuit.
• Current Rating: Ensure the barrel jack can handle the current required by your circuit. Exceeding the current rating may cause overheating or failure.
• Secure Connections: Use heat shrink tubing or electrical tape to insulate soldered connections and prevent short circuits.
• Test Before Use: After wiring the barrel jack, test the voltage and polarity with a multimeter before connecting it to your circuit.

The Arduino UNO has a 2.1mm DC barrel jack for external power. To power the Arduino using this jack:

1. Use a DC power adapter with a 2.1mm plug, providing 7-12V DC.
2. Plug the adapter into the barrel jack on the Arduino UNO.
3. Ensure the adapter is center-positive to avoid damaging the board.

Here’s an example Arduino sketch to test the power connection:

// Simple LED blink test to verify power connection
// Connect an LED to pin 13 with a 220-ohm resistor

void setup() {
  pinMode(13, OUTPUT); // Set pin 13 as an output
}

void loop() {
  digitalWrite(13, HIGH); // Turn the LED on
  delay(1000);            // Wait for 1 second
  digitalWrite(13, LOW);  // Turn the LED off
  delay(1000);            // Wait for 1 second
}

1. No Power to the Circuit:

   • Cause: Incorrect polarity or loose connections.
   • Solution: Verify the polarity of the power supply and check all connections for proper soldering or tightness.

2. Overheating Barrel Jack:

   • Cause: Exceeding the current rating of the jack.
   • Solution: Use a barrel jack with a higher current rating or reduce the load on your circuit.

3. Intermittent Power Loss:

   • Cause: Poor contact between the plug and jack.
   • Solution: Ensure the plug is fully inserted and check for dirt or debris in the jack.

4. Switch Pin Not Working:

   • Cause: Incorrect wiring or incompatible jack model.
   • Solution: Verify the wiring and ensure your jack has a functional switch pin.

Q: Can I use a 2.5mm plug with a 2.1mm barrel jack?
A: No, a 2.5mm plug will not make proper contact with a 2.1mm barrel jack, leading to unreliable connections.

Q: Is the center pin always positive?
A: Most 2.1mm barrel jacks are center-positive, but you should always verify the polarity of your power supply and jack.

Q: Can I use the barrel jack for AC power?
A: No, the 2.1mm DC barrel jack is designed for DC power only. Using it with AC power can damage your circuit and pose safety risks.

Q: How do I know if my barrel jack is rated for my circuit?
A: Check the voltage and current ratings of the barrel jack in its datasheet and ensure they meet or exceed the requirements of your circuit.