Reading I2C sensor data in Arduino - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this I2C sensor reading code?

Consider this Arduino code snippet that reads a byte from an I2C sensor at address 0x40. What will be printed on the Serial Monitor?

Arduino

Wire.begin();
Wire.beginTransmission(0x40);
Wire.write(0x00);
Wire.endTransmission();
Wire.requestFrom(0x40, 1);
int data = Wire.read();
Serial.println(data);

A Compilation error due to missing setup() and loop()

B Prints the byte value read from the sensor (e.g., 42)

C Prints 0 because Wire.read() returns 0 if no data

D Runtime error because Wire.requestFrom() is missing parameters

💡 Hint

Wire.requestFrom() asks the sensor for bytes, and Wire.read() reads them. The sensor returns a byte, which is printed.

The code correctly requests 1 byte from the sensor at address 0x40 and reads it. The value printed is the sensor's byte, not zero or error.

🧠 Conceptual

intermediate

Which I2C function initiates communication with a sensor?

In Arduino I2C communication, which function starts talking to a sensor device?

A Wire.endTransmission()

B Wire.requestFrom(address, quantity)

C Wire.read()

D Wire.beginTransmission(address)

💡 Hint

Think about which function tells the sensor you want to send data first.

Wire.beginTransmission(address) starts communication by telling the sensor you want to send data.

🔧 Debug

advanced

Why does this I2C sensor reading code always print -1?

Look at this Arduino code snippet. It always prints -1. Why?

Arduino

Wire.begin();
Wire.requestFrom(0x50, 1);
int val = Wire.read();
Serial.println(val);

A Wire.begin() must be called inside loop() to work

B Wire.read() returns -1 when the sensor address is wrong

C The sensor was not told which register to read before requesting data

D Serial.println() cannot print integers from Wire.read()

💡 Hint

Think about what the sensor expects before sending data.

The sensor needs a register address sent first with Wire.beginTransmission() and Wire.write() before Wire.requestFrom(). Without this, no data is ready, so Wire.read() returns -1.

📝 Syntax

advanced

Which option fixes the syntax error in this I2C code?

Find the option that fixes the syntax error in this Arduino I2C code snippet:

Wire.beginTransmission(0x68)
Wire.write(0x10);
Wire.endTransmission();

A Add a semicolon after Wire.beginTransmission(0x68);

B Replace Wire.endTransmission() with Wire.endTransmission(1)

C Add Wire.requestFrom(0x68, 1); after endTransmission()

D Change Wire.write(0x10) to Wire.write(0x10);

💡 Hint

Look carefully at missing punctuation in the code.

The first line is missing a semicolon at the end, causing a syntax error. Adding it fixes the code.

🚀 Application

expert

How many bytes will be read by this I2C code snippet?

This Arduino code requests data from an I2C sensor. How many bytes will be read and printed?

Wire.beginTransmission(0x20);
Wire.write(0x01);
Wire.endTransmission();
Wire.requestFrom(0x20, 3);
while(Wire.available()) {
  Serial.print(Wire.read());
  Serial.print(",");
}

A 3 bytes

B 4 bytes

C 0 bytes

D 1 byte

💡 Hint

Check the number requested in Wire.requestFrom() and how many bytes are printed.

The code requests 3 bytes from the sensor and prints each byte while available, so 3 bytes are read and printed.