I2C scanner sketch in Arduino

Introduction

An I2C scanner sketch helps you find devices connected to your Arduino's I2C bus. It tells you the addresses of all connected I2C devices so you know where to talk to them.

You want to check if your sensor or module is properly connected via I2C.

You are unsure about the I2C address of a new device you connected.

You want to find all I2C devices connected to your Arduino for troubleshooting.

You want to avoid address conflicts between multiple I2C devices.

You want to verify wiring and connections before writing code to communicate.

Syntax

Arduino

for (byte address = 1; address < 127; address++) {
  Wire.beginTransmission(address);
  byte error = Wire.endTransmission();
  if (error == 0) {
    // Device found at this address
  }
}

This loop tries to communicate with every possible I2C address from 1 to 126.

If the device responds without error, it means a device is present at that address.

Examples

This example initializes I2C and prints the address of each found device in hexadecimal.

Arduino

Wire.begin();
Serial.begin(9600);
for (byte address = 1; address < 127; address++) {
  Wire.beginTransmission(address);
  byte error = Wire.endTransmission();
  if (error == 0) {
    Serial.print("Device found at address 0x");
    Serial.println(address, HEX);
  }
}

This example scans a smaller range of addresses and prints them in decimal.

Arduino

Wire.begin();
Serial.begin(9600);
for (byte address = 8; address < 120; address++) {
  Wire.beginTransmission(address);
  byte error = Wire.endTransmission();
  if (error == 0) {
    Serial.print("Found device at ");
    Serial.println(address);
  }
}

Sample Program

This complete sketch scans all possible I2C addresses and prints each found device's address in hexadecimal format. It also prints how many devices were found or if none were found.

Arduino

#include <Wire.h>

void setup() {
  Wire.begin();
  Serial.begin(9600);
  while (!Serial); // Wait for Serial to be ready
  Serial.println("I2C Scanner starting...");

  byte count = 0;
  for (byte address = 1; address < 127; address++) {
    Wire.beginTransmission(address);
    byte error = Wire.endTransmission();
    if (error == 0) {
      Serial.print("I2C device found at address 0x");
      if (address < 16) Serial.print("0");
      Serial.println(address, HEX);
      count++;
    }
  }
  if (count == 0) {
    Serial.println("No I2C devices found.");
  } else {
    Serial.print(count);
    Serial.println(" device(s) found.");
  }
}

void loop() {
  // Nothing to do here
}

Important Notes

Make sure your I2C devices are powered and connected correctly before running the scanner.

Some devices may not respond to scanning if they require special initialization.

The scanner uses the Wire library, which is standard for Arduino I2C communication.

Summary

An I2C scanner helps find all devices connected to the I2C bus by checking each address.

It prints the addresses of devices found so you can use them in your programs.

Running this sketch is a quick way to check wiring and device presence.

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