I2C scanner sketch in Arduino - Mini Project: Build & Apply

I2C Scanner Sketch

📖 Scenario: You have connected several devices to your Arduino's I2C bus. You want to find out which devices are connected and their addresses.

🎯 Goal: Build a simple Arduino sketch that scans all possible I2C addresses and prints the addresses of connected devices to the Serial Monitor.

📋 What You'll Learn

Create a variable to store the starting I2C address

Create a variable to store the ending I2C address

Use a for loop to scan all addresses from start to end

Use Wire.beginTransmission() and Wire.endTransmission() to check if a device responds

Print the found device addresses in hexadecimal format to the Serial Monitor

💡 Why This Matters

🌍 Real World

This sketch helps you find the addresses of I2C devices connected to your Arduino, which is useful when setting up sensors or displays.

💼 Career

Understanding how to scan and communicate with I2C devices is important for embedded systems and hardware interfacing jobs.

1

Setup I2C scanning range

Create two integer variables called startAddress and endAddress. Set startAddress to 1 and endAddress to 127.

Arduino

# Create two integer variables startAddress and endAddress with values 1 and 127
# Your code here

Hint

Use int to create the variables and assign the numbers 1 and 127 exactly.

2

Initialize I2C and Serial communication

Add the Wire.h library include. In the setup() function, start the I2C bus with Wire.begin() and start serial communication at 9600 baud with Serial.begin(9600).

Arduino

int startAddress = 1;
int endAddress = 127;

#include 

void setup() {
  // Initialize I2C and Serial communication
  // Your code here
}

void loop() {
  // Empty loop
}

Hint

Remember to include Wire.h at the top. Use Wire.begin() and Serial.begin(9600) inside setup().

3

Scan I2C addresses

Inside the setup() function, add a for loop that uses address from startAddress to endAddress. For each address, call Wire.beginTransmission(address) and then Wire.endTransmission(). If Wire.endTransmission() returns 0, print "Found device at 0x" followed by the address in hexadecimal format using Serial.print(address, HEX) and then print a new line with Serial.println().

Arduino

int startAddress = 1;
int endAddress = 127;

#include 

void setup() {
  Wire.begin();
  Serial.begin(9600);

  // Add for loop to scan addresses
  // Your code here
}

void loop() {
  // Empty loop
}

Hint

Use a for loop with address from startAddress to endAddress. Check if Wire.endTransmission() returns 0 to detect a device.

4

Print scan completion message

After the for loop inside setup(), add a line to print "Scan complete." to the Serial Monitor using Serial.println().

Arduino

int startAddress = 1;
int endAddress = 127;

#include 

void setup() {
  Wire.begin();
  Serial.begin(9600);

  for (int address = startAddress; address <= endAddress; address++) {
    Wire.beginTransmission(address);
    if (Wire.endTransmission() == 0) {
      Serial.print("Found device at 0x");
      Serial.println(address, HEX);
    }
  }
  // Print scan complete message
  // Your code here
}

void loop() {
  // Empty loop
}

Hint

Use Serial.println("Scan complete.") after the loop to show the scan is done.

Practice

1. What is the main purpose of an I2C scanner sketch in Arduino programming?

easy

A. To reset the Arduino board automatically

B. To detect and list all devices connected on the I2C bus

C. To send data to all I2C devices simultaneously

D. To measure voltage levels on the I2C pins

Solution

1. Step 1: Understand the role of I2C scanner

   An I2C scanner checks each possible address on the I2C bus to find connected devices.

2. Step 2: Identify the main function

   The main function is to detect and list all devices so you know which addresses are in use.

3. Final Answer:

   To detect and list all devices connected on the I2C bus -> Option B

4. Quick Check:

   I2C scanner = device finder [OK]

Hint: I2C scanner finds devices by checking addresses [OK]

Common Mistakes:

• Thinking it sends data to devices
• Confusing it with board reset functions
• Assuming it measures electrical signals

2. Which of the following is the correct way to start the I2C communication in an Arduino I2C scanner sketch?

easy

A. Wire.begin();

B. Wire.start();

C. Wire.init();

D. Wire.connect();

Solution

1. Step 1: Recall the Wire library initialization

   The Wire library uses Wire.begin(); to start I2C communication.

2. Step 2: Check other options

   Functions like Wire.start();, Wire.init();, and Wire.connect(); do not exist in the Wire library.

3. Final Answer:

   Wire.begin(); -> Option A

4. Quick Check:

   Start I2C with Wire.begin() [OK]

Hint: Use Wire.begin() to start I2C communication [OK]

Common Mistakes:

• Using non-existent Wire functions
• Confusing with other library methods
• Omitting Wire.begin() causing no communication

3. Consider this snippet from an I2C scanner sketch:

for (byte address = 1; address < 127; address++) {
  Wire.beginTransmission(address);
  byte error = Wire.endTransmission();
  if (error == 0) {
    Serial.print("Device found at 0x");
    Serial.println(address, HEX);
  }
}

What will this code print if devices are found at addresses 8 and 42?

medium

A. Device found at 0x8\nDevice found at 0x2A

B. Device found at 0x08\nDevice found at 0x2A

C. Device found at 0x08\nDevice found at 0x42

D. Device found at 0x8\nDevice found at 0x42

Solution

1. Step 1: Understand the address printing format

   The code prints the address in hexadecimal using Serial.println(address, HEX);. Hex 8 is '8', hex 42 decimal is '2A'.

2. Step 2: Check leading zeros

   Since Serial.println() with HEX does not pad zeros, 8 prints as '8', 42 prints as '2A'.

3. Final Answer:

   Device found at 0x8\nDevice found at 0x2A -> Option A

4. Quick Check:

   Hex 8 = 8, Hex 42 = 2A [OK]

Hint: Hex print does not add leading zeros by default [OK]

Common Mistakes:

• Assuming leading zeros appear automatically
• Confusing decimal 42 with hex 42
• Expecting uppercase letters always

4. You wrote this I2C scanner code but it never finds any devices:

for (byte address = 0; address <= 127; address++) {
  Wire.beginTransmission(address);
  byte error = Wire.endTransmission();
  if (error == 0) {
    Serial.print("Found device at ");
    Serial.println(address, HEX);
  }
}

What is the likely problem?

medium

A. Wire.endTransmission() must be called twice

B. Address 0 is reserved and should not be scanned

C. The loop should start from 1, not 0

D. Serial.print() cannot print HEX values

Solution

1. Step 1: Check the address range in the loop

   The I2C valid addresses range from 1 to 127. Starting at 0 is invalid and may cause issues.

2. Step 2: Understand scanning addresses

   Starting from 1 avoids reserved addresses and ensures proper scanning.

3. Final Answer:

   The loop should start from 1, not 0 -> Option C

4. Quick Check:

   Scan addresses 1 to 127 [OK]

Hint: Start scanning from address 1, not 0 [OK]

Common Mistakes:

• Including address 0 which is reserved
• Calling Wire.endTransmission() multiple times unnecessarily
• Thinking Serial.print() can't print HEX

5. You want to modify an I2C scanner sketch to skip addresses where Wire.endTransmission() returns 4 (other error) and print a summary count of devices found at the end. Which code snippet correctly implements this?

hard

A. int count = 0;
for (byte addr = 1; addr < 128; addr++) {
Wire.beginTransmission(addr);
byte error = Wire.endTransmission();
if (error == 0) {
Serial.print("Device at 0x"); Serial.println(addr, HEX);
count++;
} else if (error == 4) {
count--;
}
}
Serial.print("Total devices: "); Serial.println(count);

B. int count = 0;
for (byte addr = 0; addr <= 127; addr++) {
Wire.beginTransmission(addr);
byte error = Wire.endTransmission();
if (error == 0) {
Serial.print("Device at 0x"); Serial.println(addr, HEX);
count++;
} else if (error == 4) {
break;
}
}
Serial.print("Total devices: "); Serial.println(count);

C. int count = 0;
for (byte addr = 1; addr < 127; addr++) {
Wire.beginTransmission(addr);
byte error = Wire.endTransmission();
if (error == 0) {
Serial.print("Device at 0x"); Serial.println(addr, HEX);
count++;
} else if (error == 4) {
Serial.println("Error 4 at address " + addr);
}
}
Serial.print("Total devices: "); Serial.println(count);

D. int count = 0;
for (byte addr = 1; addr < 127; addr++) {
Wire.beginTransmission(addr);
byte error = Wire.endTransmission();
if (error == 0) {
Serial.print("Device at 0x"); Serial.println(addr, HEX);
count++;
} else if (error == 4) {
continue;
}
}
Serial.print("Total devices: "); Serial.println(count);

Solution

1. Step 1: Set correct address range and initialize count

   The loop must scan addresses 1 to 126 (less than 127). Initialize count to zero before loop.

2. Step 2: Handle error 4 by skipping and count devices found

   If error is 0, print address and increment count. If error is 4, skip with continue to avoid stopping the scan.

3. Step 3: Print total devices after loop

   After scanning, print the total count of devices found.

4. Final Answer:

   Code snippet A correctly implements the requirements -> Option D

5. Quick Check:

   Skip error 4 with continue, count devices [OK]

Hint: Use continue to skip error 4 and count devices found [OK]

Common Mistakes:

• Using break instead of continue on error 4
• Starting loop at 0 instead of 1
• Decreasing count on error instead of skipping