Why I2C is used in Embedded C - See It in Action

Why I2C is used

📖 Scenario: You are working on a small embedded system that needs to communicate with multiple sensors and devices using only a few wires.

🎯 Goal: Understand why the I2C communication protocol is used by creating a simple program that sets up device addresses and demonstrates communication over I2C.

📋 What You'll Learn

Create a list of device addresses connected to the I2C bus

Set a variable for the maximum number of devices allowed on the bus

Write a loop to check which devices are connected by comparing addresses

Print the addresses of connected devices

💡 Why This Matters

🌍 Real World

I2C is used in embedded systems to connect sensors, displays, and other components with minimal wiring.

💼 Career

Understanding I2C helps in designing efficient hardware communication for microcontrollers and embedded devices.

1

Create a list of I2C device addresses

Create an array called device_addresses with these exact values: 0x3C, 0x27, 0x68, 0x40.

Embedded C

# Create an array called device_addresses with the given I2C addresses
// Your code here

Hint

Use curly braces to list the addresses inside the array.

2

Set the maximum number of devices

Create an integer variable called max_devices and set it to 4.

Embedded C

unsigned char device_addresses[] = {0x3C, 0x27, 0x68, 0x40};
// Create an int variable max_devices and set it to 4
// Your code here

Hint

Use int to declare the variable and assign the value 4.

3

Check connected devices using a loop

Write a for loop using int i from 0 to less than max_devices. Inside the loop, create an if statement that checks if device_addresses[i] is not zero. If true, call a function check_device(device_addresses[i]).

Embedded C

unsigned char device_addresses[] = {0x3C, 0x27, 0x68, 0x40};
int max_devices = 4;
// Loop through device_addresses and call check_device for each non-zero address
// Your code here

Hint

Use a for loop with i from 0 to max_devices - 1. Inside, use if to check the address and call the function.

4

Print connected device addresses

Write a for loop using int i from 0 to less than max_devices. Inside the loop, print the text "Device found at address: 0x" followed by the hexadecimal value of device_addresses[i] using printf.

Embedded C

unsigned char device_addresses[] = {0x3C, 0x27, 0x68, 0x40};
int max_devices = 4;

for (int i = 0; i < max_devices; i++) {
    if (device_addresses[i] != 0) {
        check_device(device_addresses[i]);
    }
}
// Print each device address in hex format
// Your code here

Hint

Use printf("Device found at address: 0x%X\n", device_addresses[i]); inside the loop.

Practice

1. Why is I2C commonly used in embedded systems?

easy

A. It uses wireless signals for communication.

B. It requires a separate wire for each device.

C. It only supports one device at a time.

D. It allows multiple devices to communicate using only two wires.

Solution

1. Step 1: Understand I2C wiring

   I2C uses two wires: SDA (data) and SCL (clock) to connect devices.

2. Step 2: Recognize multi-device communication

   Multiple devices share these two wires, communicating by unique addresses.

3. Final Answer:

   It allows multiple devices to communicate using only two wires. -> Option D

4. Quick Check:

   I2C uses 2 wires for many devices [OK]

Hint: I2C uses 2 wires for many devices, not one per device [OK]

Common Mistakes:

• Thinking each device needs its own wire
• Confusing I2C with wireless communication
• Believing only one device can connect

2. Which of the following is the correct way to describe I2C communication lines?

easy

A. Separate data and clock lines for each device

B. Only one wire for both data and clock

C. Single data line and single clock line shared by all devices

D. Wireless data and wired clock lines

Solution

1. Step 1: Identify I2C lines

   I2C uses two lines: SDA for data and SCL for clock.

2. Step 2: Understand line sharing

   Both lines are shared by all devices on the bus, not separate per device.

3. Final Answer:

   Single data line and single clock line shared by all devices -> Option C

4. Quick Check:

   I2C shares SDA and SCL lines [OK]

Hint: I2C shares one data and one clock line for all devices [OK]

Common Mistakes:

• Assuming separate lines per device
• Thinking data and clock share one wire
• Confusing wireless with wired lines

3. You want to connect 5 sensors to a microcontroller using I2C. What is the main advantage of using I2C here?

easy

A. Each sensor needs its own data and clock wires

B. You can use only two wires total for all sensors

C. Sensors communicate wirelessly with microcontroller

D. I2C requires no addressing for devices

Solution

1. Step 1: Understand wiring for multiple devices

   I2C allows multiple devices to share the same two wires: SDA and SCL.

2. Step 2: Recognize wiring advantage

   This saves pins and wiring complexity compared to separate wires per sensor.

3. Final Answer:

   You can use only two wires total for all sensors -> Option B

4. Quick Check:

   Two wires for many devices saves pins [OK]

Hint: I2C uses 2 wires total regardless of device count [OK]

Common Mistakes:

• Thinking each sensor needs separate wires
• Assuming I2C is wireless
• Believing devices don't need addresses

4. Consider this I2C communication snippet in embedded C:

i2c_start();
i2c_write(0x50); // device address
uint8_t data = i2c_read();
i2c_stop();
printf("%d", data);

What does this code do?

medium

A. Starts I2C, writes device address, reads one byte, stops, prints data

B. Starts I2C, reads device address, writes one byte, stops, prints data

C. Starts I2C, writes data, reads address, stops, prints data

D. Starts I2C, stops immediately, prints zero

Solution

1. Step 1: Analyze I2C function calls

   i2c_start() begins communication, i2c_write(0x50) sends device address.

2. Step 2: Understand data flow

   i2c_read() reads one byte from the device, i2c_stop() ends communication, printf prints the data.

3. Final Answer:

   Starts I2C, writes device address, reads one byte, stops, prints data -> Option A

4. Quick Check:

   Write address, read data, stop, print [OK]

Hint: Write address before reading data in I2C [OK]

Common Mistakes:

• Mixing read and write order
• Assuming stop happens before read
• Confusing address with data

5. This embedded C code tries to communicate over I2C but fails:

i2c_write(0x50);
i2c_start();
i2c_read();
i2c_stop();

What is the main error?

medium

A. Calling i2c_write before i2c_start

B. Missing device address in i2c_write

C. Not calling i2c_stop before i2c_start

D. Reading data before writing device address

Solution

1. Step 1: Check function call order

   i2c_start() must be called before i2c_write() to begin communication.

2. Step 2: Identify error

   Here, i2c_write() is called before i2c_start(), which is incorrect and causes failure.

3. Final Answer:

   Calling i2c_write before i2c_start -> Option A

4. Quick Check:

   Start communication before writing [OK]

Hint: Always call i2c_start() before i2c_write() [OK]

Common Mistakes:

• Writing before starting communication
• Ignoring function call order
• Assuming stop must come before start