I2C Communication between Two Microcontrollers

In this tutorial, we will learn how to set up and implement I2C communication between two microcontrollers (e.g., two Arduino boards). The I2C protocol is widely used for communication between microcontrollers and peripheral devices like sensors, displays, and EEPROMs.

Components Required

• 2 x Arduino boards (any models, such as Uno, Mega, or Nano)
• Breadboard and jumper wires
• Optional: Pull-up resistors (4.7 kΩ or 10 kΩ)
• USB cables for uploading the code

Understanding I2C

I2C (Inter-Integrated Circuit) is a two-wire communication protocol used in embedded systems to enable multiple devices to communicate over a shared bus. Here’s an overview:

• SDA (Serial Data Line): Used for data exchange between devices.
• SCL (Serial Clock Line): Provides the clock signal for synchronization.

One device is designated as the master, which controls the clock and initiates communication, while other devices act as slaves.

Wiring the Arduinos

Follow the steps below to connect two Arduino boards for I2C communication:

• Connect the SDA pin (A4 on Uno) of the master Arduino to the SDA pin of the slave Arduino.
• Connect the SCL pin (A5 on Uno) of the master Arduino to the SCL pin of the slave Arduino.
• Connect the GND of both Arduinos together.

If you experience instability, add 4.7 kΩ pull-up resistors to the SDA and SCL lines.

Arduino Code

Master Arduino Code

#include 

void setup() {
  Wire.begin(); // Initialize I2C as master
  Serial.begin(9600);
}

void loop() {
  Wire.beginTransmission(8); // Address of slave
  Wire.write("Hello Slave!"); // Send message
  Wire.endTransmission();
  delay(1000); // Wait 1 second
}
            

Slave Arduino Code

#include 

void setup() {
  Wire.begin(8); // Initialize I2C with address 8
  Wire.onReceive(receiveEvent); // Set up receive event
  Serial.begin(9600);
}

void receiveEvent(int bytes) {
  while (Wire.available()) {
    char c = Wire.read();
    Serial.print(c);
  }
  Serial.println();
}

void loop() {
  // The slave operates passively
}
            

Upload and Test

1. Connect the master Arduino to your PC and upload the master code.
2. Repeat the process for the slave Arduino, uploading the slave code.
3. Open the serial monitor for the slave Arduino to see the data received from the master.

You should see the message "Hello Slave!" printed on the slave Arduino’s serial monitor every second.

Common Errors

Here are common issues and solutions:

• No Data Received: Check wiring and ensure both devices are on the same ground.
• Incorrect Slave Address: Ensure the slave address in Wire.begin() matches the address in the master code.
• Unstable Communication: Add pull-up resistors to SDA and SCL lines.

Advanced Applications

Once you’ve mastered basic I2C communication, explore these advanced uses:

• Integrate multiple slave devices (e.g., sensors, displays) with unique addresses.
• Use I2C for real-time data exchange in robotics projects.
• Combine I2C with SPI for hybrid communication setups.

Conclusion

In this tutorial, you learned how to set up and implement I2C communication between two Arduino boards. This communication protocol is versatile and can be extended to multiple devices or used with various peripherals.