Connecting multiple I2C devices in Arduino - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output when scanning I2C devices?

This Arduino code scans the I2C bus for connected devices and prints their addresses. What will it print if two devices with addresses 0x3C and 0x68 are connected?

Arduino

void setup() {
  Wire.begin();
  Serial.begin(9600);
  while (!Serial);
  Serial.println("Scanning I2C devices...");
  for (byte address = 1; address < 127; address++) {
    Wire.beginTransmission(address);
    byte error = Wire.endTransmission();
    if (error == 0) {
      Serial.print("Device found at 0x");
      if (address < 16) Serial.print("0");
      Serial.println(address, HEX);
    }
  }
  Serial.println("Scan complete.");
}

void loop() {}

A Scanning I2C devices...\nDevice found at 0x3C\nDevice found at 0x68\nScan complete.

B Scanning I2C devices...\nDevice found at 0x3C\nScan complete.

C Scanning I2C devices...\nDevice found at 0x68\nScan complete.

D Scanning I2C devices...\nScan complete.

💡 Hint

Think about how the code checks all addresses from 1 to 126 and prints each device found.

The code scans all possible I2C addresses and prints each device found. Since devices at 0x3C and 0x68 respond, both addresses are printed.

🧠 Conceptual

intermediate

Why do multiple I2C devices need unique addresses?

When connecting multiple I2C devices to the same bus, why must each device have a unique address?

A To prevent data collisions and ensure the master communicates with the correct device.

B Because devices with the same address will increase the bus speed automatically.

C To allow devices to share power lines without interference.

D Because the master can only communicate with one device at a time regardless of address.

💡 Hint

Think about how the master identifies devices on the bus.

Each I2C device must have a unique address so the master can select and communicate with the correct device without confusion or data collision.

🔧 Debug

advanced

Why does this code fail to properly detect the second I2C device?

The code below is intended to scan for two I2C devices at addresses 0x20 and 0x21. However, it only properly detects the device at 0x20. What is the problem?

Arduino

void setup() {
  Wire.begin();
  Serial.begin(9600);
  Serial.println("Scanning I2C devices...");
  Wire.beginTransmission(0x20);
  if (Wire.endTransmission() == 0) {
    Serial.println("Device found at 0x20");
  }
  Wire.beginTransmission(0x21);
  Wire.endTransmission();
  Serial.println("Device found at 0x21");
}

void loop() {}

A The Wire.beginTransmission(0x21) call is missing, so the device at 0x21 is never checked.

B The Serial.begin(9600) is called too late, causing output issues.

C The code prints 'Device found at 0x21' regardless of device presence because it does not check the return value of endTransmission for 0x21.

D The code should use Wire.requestFrom() instead of beginTransmission to detect devices.

💡 Hint

Look carefully at how the code checks for the device at 0x21.

The code calls Wire.endTransmission() for 0x21 but does not check its return value. It prints the device found message unconditionally, so it always prints that 0x21 is found even if it is not.

📝 Syntax

advanced

Which code snippet correctly initializes two I2C devices with different addresses?

Choose the code snippet that correctly initializes two I2C devices with addresses 0x40 and 0x41 using the Wire library.

A Wire.begin();\nWire.requestFrom(0x40, 1);\nWire.requestFrom(0x41, 1);

B Wire.begin(0x40);\nWire.begin(0x41);

C Wire.begin();\nWire.begin(0x40);\nWire.begin(0x41);

D Wire.begin();\nWire.beginTransmission(0x40);\nWire.endTransmission();\nWire.beginTransmission(0x41);\nWire.endTransmission();

💡 Hint

Remember that Wire.begin() initializes the master and beginTransmission starts communication with a device.

Wire.begin() initializes the I2C master. To communicate with devices, beginTransmission and endTransmission are used with each device's address. Options B and C misuse begin(), and A uses requestFrom which reads data but does not initialize devices.

🚀 Application

expert

How to handle two I2C devices with the same fixed address?

You have two I2C sensors that both use the fixed address 0x50 and cannot be changed. How can you connect and use both sensors on the same Arduino I2C bus?

A Change the Arduino's I2C address to avoid conflicts with the devices.

B Use an I2C multiplexer to switch between the two devices, selecting one at a time.

C Connect both devices directly to the bus; the Arduino will automatically handle address conflicts.

D Use two separate Arduino boards, each connected to one sensor, and communicate between Arduinos.

💡 Hint

Think about hardware solutions to address conflicts on the I2C bus.

When two devices have the same fixed address, an I2C multiplexer can isolate one device at a time, allowing the master to communicate without address conflicts. The Arduino cannot change device addresses or handle conflicts automatically.