How to Use RELAY SRD-05VDC-SL-C: Examples, Pinouts, and Specs

The SRD-05VDC-SL-C is a compact electromagnetic relay manufactured by SONGLE. It operates at a 5V DC input and is widely used in electronic circuits for switching applications. This relay features a Single Pole Double Throw (SPDT) configuration, enabling it to control high-voltage or high-current devices using a low-voltage control signal. Its versatility and reliability make it a popular choice for automation, home appliances, and IoT projects.

• Home automation systems (e.g., controlling lights, fans, or appliances)
• Industrial control systems
• IoT projects for remote device control
• Motor control circuits
• Power supply switching

Below are the key technical details of the SRD-05VDC-SL-C relay:

The SRD-05VDC-SL-C relay has 5 pins, as described in the table below:

1. Power the Relay Coil: Connect the coil pins (1 and 2) to a 5V DC power source. Pin 1 should be connected to the positive terminal, and Pin 2 to ground.
2. Control the Relay: Use a microcontroller (e.g., Arduino) or a transistor to control the relay coil. When the coil is energized, the relay switches from the NC contact to the NO contact.
3. Connect the Load:
   • Connect the device or circuit you want to control to the COM and NO pins if you want it to turn on when the relay is activated.
   • Use the COM and NC pins if you want the device to turn off when the relay is activated.
4. Add a Flyback Diode: Place a diode (e.g., 1N4007) across the coil terminals to protect the circuit from voltage spikes caused by the relay's inductive load.

Below is an example of how to control the SRD-05VDC-SL-C relay using an Arduino UNO:

• Relay Pin 1 (Coil +): Connect to Arduino digital pin (e.g., D7) through a 1kΩ resistor.
• Relay Pin 2 (Coil -): Connect to Arduino GND.
• Relay COM Pin: Connect to one terminal of the load (e.g., a light bulb).
• Relay NO Pin: Connect to the power source for the load.
• Relay NC Pin: Leave unconnected (optional, depending on use case).

// Define the pin connected to the relay
const int relayPin = 7;

void setup() {
  // Set the relay pin as an output
  pinMode(relayPin, OUTPUT);
  
  // Start with the relay off
  digitalWrite(relayPin, LOW);
}

void loop() {
  // Turn the relay on (activates the NO contact)
  digitalWrite(relayPin, HIGH);
  delay(1000); // Keep the relay on for 1 second
  
  // Turn the relay off (deactivates the NO contact)
  digitalWrite(relayPin, LOW);
  delay(1000); // Keep the relay off for 1 second
}

• Power Supply: Ensure the relay coil is powered with a stable 5V DC source. Using a higher voltage may damage the relay.
• Isolation: For safety, use an optocoupler or transistor to isolate the control circuit from the relay.
• Load Ratings: Do not exceed the relay's maximum contact ratings (10A @ 250V AC or 10A @ 30V DC).
• Mounting: Secure the relay on a PCB or breadboard to prevent loose connections.

1. Relay Not Switching:

   • Cause: Insufficient voltage or current to the coil.
   • Solution: Verify that the coil is receiving 5V DC and check the control circuit.

2. Load Not Turning On/Off:

   • Cause: Incorrect wiring of the COM, NO, or NC pins.
   • Solution: Double-check the connections and ensure the load is properly connected.

3. Relay Buzzing Noise:

   • Cause: Unstable power supply or insufficient current to the coil.
   • Solution: Use a stable 5V DC power source and ensure the control circuit can supply enough current.

4. Overheating:

   • Cause: Exceeding the relay's contact ratings.
   • Solution: Ensure the load does not exceed 10A or the specified voltage limits.

Q1: Can I use the SRD-05VDC-SL-C with a 3.3V microcontroller?
A1: Yes, but you will need a transistor or relay driver circuit to step up the control signal to 5V.

Q2: Is the relay suitable for switching DC motors?
A2: Yes, as long as the motor's voltage and current are within the relay's contact ratings. Use a flyback diode to protect the circuit from voltage spikes.

Q3: Can I use the relay for high-frequency switching?
A3: No, the SRD-05VDC-SL-C is not designed for high-frequency switching. It is best suited for low-frequency applications.

Q4: What is the lifespan of the relay?
A4: The relay has a mechanical lifespan of approximately 10 million operations and an electrical lifespan of around 100,000 operations under rated load conditions.