How to Use 1 Channel Relay module with Optocoupler: Examples, Pinouts, and Specs

The 1 Channel Relay Module with Optocoupler (Manufacturer: Songle, Part ID: SRD-05VDC-SL-C) is a versatile electronic component designed to control high-voltage devices using low-voltage signals. This module integrates an optocoupler to provide electrical isolation between the control circuit and the load, ensuring safety and protecting sensitive components from voltage spikes or interference.

• Home automation systems (e.g., controlling lights, fans, or appliances)
• Industrial control systems
• Robotics and IoT projects
• Motor control
• Switching high-power devices using microcontrollers like Arduino, Raspberry Pi, or ESP32

The relay module has a total of 6 pins and terminals, divided into two sections: control pins and load terminals.

1. Power the Module: Connect the VCC pin to a 5V DC power supply and the GND pin to the ground.
2. Control Signal: Connect the IN pin to a digital output pin of a microcontroller (e.g., Arduino). When the IN pin receives a HIGH signal (3.3V-5V), the relay will activate.
3. Load Connection:
   • Connect the load (e.g., a light bulb or motor) to the COM terminal.
   • Depending on the desired behavior:
     • Use the NO terminal for a default OFF state (load turns ON when the relay is activated).
     • Use the NC terminal for a default ON state (load turns OFF when the relay is activated).
4. Isolation: The optocoupler ensures that the control circuit is electrically isolated from the high-voltage load, enhancing safety.

• Power Supply: Ensure the module is powered with a stable 5V DC supply.
• Load Ratings: Do not exceed the maximum load voltage (250V AC / 30V DC) or current (10A).
• Flyback Diode: If controlling an inductive load (e.g., motor or solenoid), use a flyback diode across the load to suppress voltage spikes.
• Signal Voltage: Ensure the control signal voltage is within the range of 3.3V to 5V.
• Safety: Avoid touching the module or load connections when the relay is operating with high voltage.

Below is an example of how to control the relay module using an Arduino UNO:

• Connect the relay module's VCC to the Arduino's 5V pin.
• Connect the relay module's GND to the Arduino's GND pin.
• Connect the relay module's IN pin to Arduino digital pin 7.
• Connect the load (e.g., a light bulb) to the COM and NO terminals 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 (activates the connected load)
  digitalWrite(relayPin, HIGH);
  delay(5000); // Keep the relay ON for 5 seconds
  
  // Turn the relay OFF (deactivates the connected load)
  digitalWrite(relayPin, LOW);
  delay(5000); // Keep the relay OFF for 5 seconds
}

1. Relay Not Activating:

   • Cause: Insufficient control signal voltage.
   • Solution: Ensure the IN pin receives a signal between 3.3V and 5V.

2. Load Not Switching:

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

3. Module Overheating:

   • Cause: Exceeding the maximum load current or voltage.
   • Solution: Ensure the load does not exceed 10A or 250V AC / 30V DC.

4. Interference in Control Circuit:

   • Cause: Voltage spikes from inductive loads.
   • Solution: Use a flyback diode across the load to suppress spikes.

Q1: Can I use this relay module with a 3.3V microcontroller like ESP32?
A1: Yes, the module can be triggered with a 3.3V control signal. Ensure the VCC pin is still powered with 5V.

Q2: Is it safe to use this module with high-voltage AC loads?
A2: Yes, but take necessary precautions. Ensure proper insulation and avoid touching the module while operating.

Q3: Can I control multiple relays with one microcontroller?
A3: Yes, as long as each relay is connected to a separate digital output pin and the microcontroller can supply sufficient current.

Q4: What is the purpose of the optocoupler?
A4: The optocoupler electrically isolates the control circuit from the high-voltage load, protecting sensitive components and enhancing safety.