How to Use I2C: Examples, Pinouts, and Specs

I2C (Inter-Integrated Circuit) is a multi-master, multi-slave, packet-switched, single-ended, serial communication bus. It is widely used in embedded systems to connect low-speed devices such as sensors, EEPROMs, real-time clocks, and microcontrollers. I2C is known for its simplicity and efficiency, requiring only two communication lines: a data line (SDA) and a clock line (SCL). This makes it ideal for applications where minimizing pin usage is critical.

• Communication between microcontrollers and peripheral devices (e.g., sensors, displays)
• Reading and writing data to EEPROMs or real-time clocks
• Interfacing with ADCs/DACs in measurement systems
• Connecting multiple devices on a shared bus in embedded systems

• Communication Type: Serial, synchronous
• Number of Wires: 2 (SDA - Serial Data, SCL - Serial Clock)
• Voltage Levels: Typically 3.3V or 5V (depending on the system)
• Speed Modes:
  • Standard Mode: Up to 100 kHz
  • Fast Mode: Up to 400 kHz
  • Fast Mode Plus: Up to 1 MHz
  • High-Speed Mode: Up to 3.4 MHz
• Addressing: 7-bit or 10-bit addressing
• Pull-Up Resistors: Required on both SDA and SCL lines (typical values: 4.7 kΩ or 10 kΩ)

I2C does not refer to a specific physical component but rather a protocol. However, devices using I2C typically have the following pins:

1. Connect the SDA and SCL Lines:
   • Connect the SDA and SCL pins of all devices on the bus.
   • Use pull-up resistors on both lines to ensure proper signal levels.
2. Power the Devices:
   • Ensure all devices share a common ground (GND).
   • Provide the appropriate voltage (3.3V or 5V) to the VCC pin of each device.
3. Assign Unique Addresses:
   • Each slave device on the I2C bus must have a unique address.
   • Check the datasheet of each device to configure or identify its address.
4. Configure the Master Device:
   • The master device (e.g., a microcontroller) initiates communication and controls the clock signal.
   • Use appropriate libraries or firmware to configure the master for I2C communication.

• Pull-Up Resistors: Ensure the SDA and SCL lines have proper pull-up resistors. Without them, the lines may not function correctly.
• Bus Length: Keep the bus length short to avoid signal degradation and interference.
• Address Conflicts: Avoid using devices with the same I2C address on the same bus. If unavoidable, consider using an I2C multiplexer.
• Clock Speed: Match the clock speed to the capabilities of all devices on the bus.
• Noise Filtering: Use decoupling capacitors near the power pins of devices to reduce noise.

Below is an example of interfacing an I2C temperature sensor (e.g., TMP102) with an Arduino UNO:

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

#define TMP102_ADDRESS 0x48 // I2C address of the TMP102 sensor

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

void loop() {
  Wire.beginTransmission(TMP102_ADDRESS); // Start communication with TMP102
  Wire.write(0x00); // Point to the temperature register
  Wire.endTransmission(); // End transmission

  Wire.requestFrom(TMP102_ADDRESS, 2); // Request 2 bytes of data from TMP102
  if (Wire.available() == 2) { // Check if 2 bytes are available
    int msb = Wire.read(); // Read the most significant byte
    int lsb = Wire.read(); // Read the least significant byte

    // Combine the bytes and calculate the temperature
    int temperature = ((msb << 8) | lsb) >> 4;
    float celsius = temperature * 0.0625; // TMP102 resolution is 0.0625°C

    Serial.print("Temperature: ");
    Serial.print(celsius);
    Serial.println(" °C");
  }

  delay(1000); // Wait 1 second before the next reading
}

1. No Communication on the Bus:

   • Cause: Missing or incorrect pull-up resistors.
   • Solution: Add 4.7 kΩ or 10 kΩ pull-up resistors to the SDA and SCL lines.

2. Devices Not Responding:

   • Cause: Address conflict or incorrect address configuration.
   • Solution: Verify the I2C address of each device and ensure they are unique.

3. Data Corruption:

   • Cause: Excessive noise or long bus length.
   • Solution: Shorten the bus length and add decoupling capacitors near the devices.

4. Clock Stretching Issues:

   • Cause: Slave device holding the clock line low for too long.
   • Solution: Check the slave device's datasheet for clock stretching behavior and adjust the master device's timeout settings.

• Q: Can I connect multiple masters on the same I2C bus?

  • A: Yes, I2C supports multi-master configurations, but arbitration is required to avoid conflicts.

• Q: What happens if two devices have the same I2C address?

  • A: Address conflicts will occur, leading to communication errors. Use an I2C multiplexer or change the address of one device if possible.

• Q: How do I calculate the pull-up resistor value?

  • A: The value depends on the bus capacitance and voltage. A typical value is 4.7 kΩ, but you can calculate it using the formula:
    ( R_{pull-up} = \frac{V_{cc}}{I_{pull-up}} ), where ( I_{pull-up} ) is the desired pull-up current (e.g., 1 mA).

• Q: Can I use I2C with 3.3V and 5V devices on the same bus?

  • A: Yes, but you may need a level shifter to safely interface devices with different voltage levels.

This documentation provides a comprehensive guide to understanding and using the I2C protocol effectively in your projects.