I2C scanner sketch in Arduino - Step-by-Step Execution

Concept Flow - I2C scanner sketch

Start setup

↓

Initialize I2C bus

↓

For each address 1 to 127

↓

Try to communicate

↓

Print address

↓

Next address

↓

End loop

↓

Print done

The sketch initializes the I2C bus, then tries to communicate with each possible device address from 1 to 127. If a device responds, it prints the address. After checking all, it prints done.

Execution Sample

Arduino

void setup() {
  Wire.begin();
  Serial.begin(9600);
  for (byte address = 1; address < 128; address++) {
    Wire.beginTransmission(address);
    byte error = Wire.endTransmission();
    if (error == 0) {
      Serial.println(address);
    }
  }
  Serial.println("Done");
}

void loop() {
  // Empty loop
}

This code scans all I2C addresses and prints those where a device responds.

Execution Table

Step	Address	Wire.beginTransmission(address)	Wire.endTransmission() result	Condition (error==0)	Action	Output
1	1	Start transmission to 1	No device (error=4)	False	No print
2	2	Start transmission to 2	No device (error=4)	False	No print
3	3	Start transmission to 3	Device found (error=0)	True	Print address	3
4	4	Start transmission to 4	No device (error=4)	False	No print
...	...	...	...	...	...	...
126	126	Start transmission to 126	No device (error=4)	False	No print
127	127	Start transmission to 127	No device (error=4)	False	No print
128	End loop	-	-	-	Print "Done"	Done

💡 Loop ends after checking address 127; 'Done' printed to signal completion.

Variable Tracker

Variable	Start	After 1	After 2	After 3	...	After 127	Final
address	N/A	1	2	3	...	127	Loop ends
error	N/A	4	4	0	...	4	N/A

Key Moments - 3 Insights

Why do we start scanning from address 1 and not 0?

Address 0 is reserved for general call in I2C, so scanning starts from 1 as shown in execution_table rows 1 and 2.

What does error code 0 mean in Wire.endTransmission()?

Error 0 means a device acknowledged the address, so the condition error==0 is true and the address is printed (see execution_table row 3).

Why do we print 'Done' after the loop?

'Done' signals the scan finished checking all addresses, as shown in the last row of execution_table.

Visual Quiz - 3 Questions

Look at the execution_table, what is the error code when a device is found at address 3?

A 4

B 1

C 0

D 255

💡 Hint

Check the 'Wire.endTransmission() result' column at step 3 in execution_table.

At which address does the loop stop scanning?

A 126

B 127

C 128

D 1

💡 Hint

Look at the 'address' variable in variable_tracker and the last rows in execution_table.

If a device responded at address 5, what would happen in the execution_table?

A error would be 0 and address 5 would be printed

B error would be 4 and no print

C loop would stop immediately

D address 5 would be skipped

💡 Hint

Refer to how address 3 is handled in execution_table row 3.

Concept Snapshot

I2C Scanner Sketch
- Initialize I2C bus with Wire.begin()
- Loop addresses 1 to 127
- Use Wire.beginTransmission(address) and Wire.endTransmission()
- If endTransmission returns 0, device found
- Print found address
- Print 'Done' after scanning all
Useful to detect connected I2C devices.

Full Transcript

This I2C scanner sketch starts by initializing the I2C bus and serial communication. It then loops through all possible I2C addresses from 1 to 127. For each address, it tries to start a transmission and ends it to check if a device responds. If the response error code is 0, it prints the address to the serial monitor. After checking all addresses, it prints 'Done' to signal the scan is complete. This helps find which devices are connected on the I2C bus.