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

The SRD-05VDC-SL-C is a 5V DC relay module manufactured by SONGLE. It is designed to enable low voltage control signals to switch high voltage devices, making it an essential component in automation, home appliances, and IoT projects. This relay features a Single Pole Double Throw (SPDT) configuration, allowing it to control a circuit by opening or closing its contacts. It is widely used in applications such as motor control, lighting systems, and smart home devices.

Below are the key technical details and pin configuration for the SRD-05VDC-SL-C relay:

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

1. Power the Relay Coil: Connect the Coil (+) pin to a 5V DC control signal and the Coil (-) pin to ground. This energizes the relay coil, causing the internal switch to toggle.
2. Connect the Load:
   • For devices that should turn ON when the relay is activated, connect the load between the Common (COM) and Normally Open (NO) pins.
   • For devices that should turn OFF when the relay is activated, connect the load between the Common (COM) and Normally Closed (NC) pins.
3. Control the Relay: Use a microcontroller (e.g., Arduino UNO) or other control circuit to provide the 5V DC signal to the relay coil.

• 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 de-energized.
• Isolation: If switching high voltage devices, ensure proper isolation between the control circuit and the load to prevent damage or hazards.
• Current Rating: Do not exceed the relay's contact rating (10A @ 250V AC or 10A @ 30V DC) to avoid overheating or damage.
• Secure Connections: Ensure all connections are secure to prevent arcing or loose contacts.

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

• Connect the Coil (+) pin of the relay to Arduino digital pin 7.
• Connect the Coil (-) pin of the relay to Arduino GND.
• Connect the load (e.g., a light bulb) between the Common (COM) and Normally Open (NO) pins.
• Use an external power source for the load if required.

// 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 (activates the load)
  digitalWrite(relayPin, HIGH);
  delay(5000); // Keep the relay ON for 5 seconds

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

1. Relay Not Activating:

   • Cause: Insufficient voltage or current to the relay coil.
   • Solution: Ensure the control signal provides at least 3.75V DC and 70mA current.

2. Load Not Switching:

   • Cause: Incorrect wiring of the load to the relay pins.
   • Solution: Verify the load is connected to the correct pins (COM, NO, or NC) based on the desired behavior.

3. Relay Buzzing Noise:

   • Cause: Insufficient or unstable power supply to the relay coil.
   • Solution: Use a stable 5V DC power source and ensure proper connections.

4. Overheating:

   • Cause: Exceeding the relay's contact rating.
   • Solution: Ensure the load does not draw more than 10A or operate at voltages higher than 250V AC or 30V DC.

• Can I use the SRD-05VDC-SL-C with a 3.3V control signal?

  • No, the relay requires a minimum of 3.75V DC to activate reliably. Use a level shifter or transistor circuit if your control signal is 3.3V.

• Is the relay suitable for switching DC motors?

  • Yes, but ensure the motor's current and voltage are within the relay's contact rating. Use a flyback diode across the motor terminals to protect the relay.

• Can I use this relay for AC loads?

  • Yes, the relay can handle up to 10A at 250V AC. Ensure proper isolation and safety precautions when working with AC loads.