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 two circuits (normally open and normally closed) with a single input signal.

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

The SRD-05VDC-SL-C relay is designed for reliable and efficient operation in a variety of applications. Below are its key technical details:

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

The SRD-05VDC-SL-C relay is straightforward to use in a variety of circuits. Below are the steps and best practices for integrating it into your project:

1. Power the Relay Coil: Connect the Coil+ pin to a 5V DC power source and the Coil- pin to ground. This powers the relay's internal coil.
2. Control the Relay: Use a microcontroller (e.g., Arduino UNO) or a transistor to control the relay. Apply a control signal (≥3.75V DC) to activate the relay.
3. Connect the Load:
   • Connect the load's power source to the COM pin.
   • For a normally open configuration, connect the load to the NO pin. The circuit will close when the relay is activated.
   • For a normally closed configuration, connect the load to the NC pin. The circuit will open when the relay is activated.

• Flyback Diode: Always use a flyback diode across the relay coil to protect your circuit from voltage spikes when the relay is deactivated.
• Isolation: Ensure proper electrical isolation between the control circuit and the high voltage 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 failure.
• Mounting: Secure the relay on a PCB or relay module for stable operation.

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

• Connect the Coil+ pin to a digital output pin on the Arduino (e.g., pin 7).
• Connect the Coil- pin to the Arduino's GND.
• Use a 1N4007 diode across the relay coil (anode to Coil-, cathode to Coil+).
• Connect the load to the COM and NO or NC pins, depending on your desired configuration.

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

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

void loop() {
  // Activate the relay (turn ON the connected device)
  digitalWrite(relayPin, HIGH);
  delay(5000); // Keep the relay ON for 5 seconds

  // Deactivate the relay (turn OFF the connected device)
  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 at least 3.75V DC and the current is ≥70 mA.

2. Load Not Switching:

   • Cause: Incorrect wiring of the load circuit.
   • Solution: Verify the connections to the COM, NO, and NC pins.

3. Relay Buzzing Noise:

   • Cause: Insufficient power supply to the relay coil.
   • Solution: Use a stable 5V DC power source with adequate current capacity.

4. Overheating:

   • Cause: Exceeding the relay's contact rating.
   • Solution: Ensure the load does not exceed 10A @ 250V AC or 10A @ 30V DC.

Q1: Can I use the SRD-05VDC-SL-C relay with a 3.3V microcontroller?
A1: Yes, but you may need a transistor or MOSFET to amplify the control signal to 5V DC.

Q2: Is the relay suitable for switching DC motors?
A2: Yes, but ensure the motor's current and voltage are within the relay's contact rating.

Q3: Can I use the relay for AC loads?
A3: Yes, the relay supports up to 250V AC with a maximum current of 10A.

Q4: Do I need an external flyback diode if I use a relay module?
A4: No, most relay modules include a built-in flyback diode. However, if you're using the standalone relay, you must add one.

By following this documentation, you can effectively integrate the SRD-05VDC-SL-C relay into your projects for reliable and efficient operation.