How to Use Relay 3.3v: Examples, Pinouts, and Specs

A Relay 3.3V is an electromechanical switch that uses a low voltage (3.3V) control signal to open or close a circuit. This allows for the control of higher voltage or high-current devices, such as motors, lights, or appliances, using a low-power control signal. Relays are widely used in automation, home appliances, and industrial control systems due to their ability to isolate the control circuit from the high-power circuit.

• Home automation systems (e.g., controlling lights or fans)
• Industrial equipment control
• Motor control circuits
• Safety systems (e.g., emergency shutoff)
• IoT projects with microcontrollers like Arduino or Raspberry Pi

The following table outlines the key technical details of the Relay 3.3V:

The Relay 3.3V typically has 5 pins. The table below describes each pin:

1. Power the Relay: Connect the VCC pin to a 3.3V power source and the GND pin to ground.
2. Control Signal: Connect the IN pin to a microcontroller or other control circuit capable of providing a 3.3V signal.
3. Load Circuit:
   • Connect the load device (e.g., a light bulb or motor) to the COM and NO pins if you want the load to turn on when the relay is activated.
   • Alternatively, connect the load to the COM and NC pins if you want the load to turn off when the relay is activated.
4. Isolation: Ensure proper electrical isolation between the control and load circuits to prevent damage to the control circuit.

• Flyback Diode: Always use a flyback diode across the relay coil to protect the control circuit from voltage spikes caused by the collapsing magnetic field when the relay is deactivated.
• Current Rating: Ensure the load current does not exceed the relay's maximum switching current (10A).
• Power Supply: Use a stable 3.3V power supply to avoid erratic relay behavior.
• Microcontroller Compatibility: If using a microcontroller like Arduino, ensure the control pin can source enough current (~70mA) or use a transistor to drive the relay.

Below is an example of how to connect and control a Relay 3.3V using an Arduino UNO:

• Connect the relay's VCC pin to the Arduino's 3.3V pin.
• Connect the relay's GND pin to the Arduino's GND pin.
• Connect the relay's IN pin to Arduino digital pin 7.
• Connect the load (e.g., a light bulb) to the COM and NO pins of the relay.

// Define the relay control pin
const int relayPin = 7;

void setup() {
  // Set the relay pin as an output
  pinMode(relayPin, OUTPUT);
  // Ensure the relay is off at startup
  digitalWrite(relayPin, LOW);
}

void loop() {
  // Turn the relay on (activate)
  digitalWrite(relayPin, HIGH);
  delay(5000); // Keep the relay on for 5 seconds

  // Turn the relay off (deactivate)
  digitalWrite(relayPin, LOW);
  delay(5000); // Keep the relay off for 5 seconds
}

1. Relay Not Activating:

   • Cause: Insufficient control voltage or current.
   • Solution: Ensure the control signal is 3.3V and the source can supply at least 70mA. Use a transistor if needed.

2. Load Not Switching:

   • Cause: Incorrect wiring of the load circuit.
   • Solution: Verify the load is connected to the correct relay terminals (COM and NO/NC).

3. Relay Clicking Rapidly:

   • Cause: Unstable control signal or power supply.
   • Solution: Use a stable 3.3V power source and check for noise in the control signal.

4. Microcontroller Resetting:

   • Cause: Voltage spikes from the relay coil.
   • Solution: Add a flyback diode across the relay coil.

Q: Can I use the Relay 3.3V with a 5V control signal?
A: No, the relay is designed for a 3.3V control signal. Using a 5V signal may damage the relay or cause erratic behavior.

Q: Can the Relay 3.3V switch both AC and DC loads?
A: Yes, the relay can switch AC loads up to 250V and DC loads up to 30V, provided the current does not exceed 10A.

Q: Do I need a separate power supply for the relay?
A: If your control circuit (e.g., Arduino) can provide a stable 3.3V and sufficient current, a separate power supply is not necessary. Otherwise, use an external 3.3V power source.

Q: How do I know if the relay is activated?
A: Many relays include an onboard LED that lights up when the relay is activated. Alternatively, you can measure continuity between the COM and NO pins.