How to Use 8-channel I2C relay module: Examples, Pinouts, and Specs

The 8-Channel I2C Relay Module by KRIDA is a versatile electronic component designed to control up to 8 relays using the I2C communication protocol. This module enables seamless integration with microcontrollers and single-board computers, allowing users to switch high-voltage devices (such as lights, fans, or appliances) using low-voltage control signals. Its compact design and I2C interface make it ideal for applications requiring multiple relay controls with minimal wiring.

• Home automation systems
• Industrial equipment control
• Robotics and IoT projects
• Smart lighting systems
• Prototyping and testing high-voltage circuits

The following table outlines the key technical details of the 8-Channel I2C Relay Module:

The module has a set of pins for power, I2C communication, and relay outputs. Below is the pin configuration:

Each relay has three terminals: COM, NO, and NC. These are used to connect the high-voltage devices.

1. Power the Module: Connect the VCC and GND pins to a 5V DC power source.
2. Connect to a Microcontroller: Use the SDA and SCL pins to connect the module to the I2C bus of your microcontroller (e.g., Arduino UNO).
3. Configure the I2C Address: If using multiple modules, adjust the I2C address using the onboard jumpers.
4. Connect High-Voltage Devices: Wire the devices to the relay terminals (COM, NO, NC) as per your switching requirements.
5. Control the Relays: Use I2C commands to activate or deactivate the relays.

• Ensure the total current drawn by the relays does not exceed the power supply's capacity.
• Use proper insulation and safety precautions when working with high-voltage devices.
• Avoid switching inductive loads (e.g., motors) without proper flyback diodes or snubber circuits to protect the relays.
• Verify the I2C address of the module to avoid conflicts with other devices on the same bus.

Below is an example code snippet to control the 8-Channel I2C Relay Module using an Arduino UNO:

#include <Wire.h> // Include the Wire library for I2C communication

#define RELAY_MODULE_ADDR 0x20 // Default I2C address of the relay module

void setup() {
  Wire.begin(); // Initialize I2C communication
  Serial.begin(9600); // Initialize serial communication for debugging

  // Turn off all relays at startup
  Wire.beginTransmission(RELAY_MODULE_ADDR);
  Wire.write(0x00); // Send command to turn off all relays
  Wire.endTransmission();
  Serial.println("Relay module initialized. All relays are OFF.");
}

void loop() {
  // Example: Turn on relay 1
  Wire.beginTransmission(RELAY_MODULE_ADDR);
  Wire.write(0x01); // Send command to turn on relay 1
  Wire.endTransmission();
  Serial.println("Relay 1 is ON.");
  delay(2000); // Wait for 2 seconds

  // Example: Turn off relay 1
  Wire.beginTransmission(RELAY_MODULE_ADDR);
  Wire.write(0x00); // Send command to turn off relay 1
  Wire.endTransmission();
  Serial.println("Relay 1 is OFF.");
  delay(2000); // Wait for 2 seconds
}

1. Relays Not Responding

   • Cause: Incorrect I2C address or wiring.
   • Solution: Verify the I2C address and ensure proper connections for SDA, SCL, VCC, and GND.

2. High-Voltage Device Not Switching

   • Cause: Incorrect wiring to the relay terminals.
   • Solution: Double-check the connections to COM, NO, and NC based on your switching requirements.

3. Module Overheating

   • Cause: Exceeding the maximum current or voltage ratings.
   • Solution: Ensure the connected devices are within the relay's rated specifications.

4. I2C Communication Errors

   • Cause: Conflicts with other devices on the I2C bus.
   • Solution: Change the module's I2C address using the onboard jumpers.

Q: Can I use this module with a 3.3V microcontroller?
A: Yes, but you will need a level shifter for the I2C lines, as the module operates at 5V.

Q: How do I change the I2C address?
A: Adjust the onboard jumpers according to the address configuration table in the module's datasheet.

Q: Can I control multiple modules on the same I2C bus?
A: Yes, as long as each module has a unique I2C address.

Q: Is the module safe for inductive loads?
A: Yes, but you should use flyback diodes or snubber circuits to protect the relays from voltage spikes.