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

A relay is an electromechanical switch that allows a low-power control signal to operate a high-power circuit. The 3.3V relay is specifically designed to operate with a 3.3V control signal, making it ideal for use with microcontrollers and other low-voltage systems. It provides electrical isolation between the control circuit and the load, ensuring safety and protecting sensitive components.

• Home automation systems (e.g., controlling lights, fans, or appliances)
• Industrial control systems
• Motor control
• IoT devices and projects
• Switching high-power AC or DC loads using low-power microcontrollers like Arduino or Raspberry Pi

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

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

Note: Some relay modules may include an onboard transistor and diode for easier interfacing with microcontrollers.

1. Power the Relay:

   • Connect the VCC pin to a 3.3V power source and the GND pin to ground.
   • Ensure the power supply can provide sufficient current (~70mA) to energize the relay coil.

2. Control the Relay:

   • Connect the IN pin to a GPIO pin of your microcontroller (e.g., Arduino UNO).
   • Set the GPIO pin HIGH (3.3V) to activate the relay and LOW (0V) to deactivate it.

3. Connect the Load:

   • Identify whether you want to use the NO (Normally Open) or NC (Normally Closed) terminal.
   • Connect one side of the load to the COM terminal and the other side to either the NO or NC terminal, depending on your application.

4. Add Protection:

   • If the relay module does not include a flyback diode, add one across the relay coil to protect the circuit from voltage spikes.
   • For inductive loads (e.g., motors), consider adding a snubber circuit to prevent arcing.

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

• Relay VCC → Arduino 3.3V
• Relay GND → Arduino GND
• Relay IN → Arduino Digital Pin 7
• Relay COM → One terminal of the load
• Relay NO → Power source for the load
• Relay NC → Leave unconnected (if using NO)

// 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
  digitalWrite(relayPin, HIGH);
  delay(5000); // Keep the relay ON for 5 seconds
  
  // Turn the relay OFF
  digitalWrite(relayPin, LOW);
  delay(5000); // Keep the relay OFF for 5 seconds
}

Important: Ensure the load connected to the relay does not exceed the relay's maximum voltage and current ratings.

• Use a separate power supply for the relay if your microcontroller cannot provide sufficient current.
• Avoid switching high-power loads frequently to extend the relay's lifespan.
• Ensure proper insulation and spacing between the high-voltage load and the low-voltage control circuit.

1. Relay Not Activating:

   • Cause: Insufficient current or incorrect wiring.
   • Solution: Verify the power supply provides 3.3V and at least 70mA. Check all connections.

2. Relay Stuck in One State:

   • Cause: Damaged relay contacts or coil.
   • Solution: Replace the relay if it is physically damaged or not functioning.

3. Microcontroller Resets When Activating the Relay:

   • Cause: Voltage spikes or insufficient power supply.
   • Solution: Add a flyback diode across the relay coil and ensure the power supply can handle the load.

4. Load Not Switching Properly:

   • Cause: Incorrect wiring of the load terminals.
   • Solution: Double-check the connections to the COM, NO, and NC terminals.

Q1: Can I use a 3.3V relay with a 5V microcontroller?
A1: Yes, but you may need a level shifter or transistor to ensure the control signal is compatible with the relay.

Q2: Can the relay handle both AC and DC loads?
A2: Yes, the relay can switch both AC and DC loads, provided they are within the specified voltage and current ratings.

Q3: Is it safe to use the relay for high-power applications?
A3: Yes, but ensure proper insulation, spacing, and adherence to the relay's maximum ratings to avoid hazards.

Q4: Why is a flyback diode necessary?
A4: A flyback diode protects the circuit from voltage spikes generated when the relay coil is de-energized.

By following this documentation, you can effectively use the 3.3V relay in your projects while ensuring safety and reliability.