Reading I2C sensor data in Arduino - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to include the Wire library for I2C communication.

Arduino

#include [1]

void setup() {
  Wire.begin();
}

void loop() {
  // sensor reading code
}

Drag options to blanks, or click blank then click option'

A<Wire.h>

B<SPI.h>

C<Servo.h>

D<EEPROM.h>

Attempts:

3 left

💡 Hint

Common Mistakes

Including SPI or Servo libraries instead of Wire.

Forgetting to include any library.

The Wire library is required for I2C communication on Arduino. Including allows you to use I2C functions.

2fill in blank

medium

Complete the code to start I2C communication as a master device.

Arduino

void setup() {
  [1]();
}

Drag options to blanks, or click blank then click option'

ASerial.begin

BWire.begin

CWire.start

DSerial.start

Attempts:

3 left

💡 Hint

Common Mistakes

Using Serial.begin instead of Wire.begin.

Using Wire.start which does not exist.

Wire.begin() initializes the Arduino as an I2C master device.

3fill in blank

hard

Fix the error in the code to request 2 bytes from the sensor at address 0x40.

Arduino

Wire.requestFrom([1], 2);

Drag options to blanks, or click blank then click option'

A0x20

B0x04

C0x40

D40

Attempts:

3 left

💡 Hint

Common Mistakes

Using decimal 40 instead of hex 0x40.

Using wrong sensor address.

The sensor address is 0x40 in hexadecimal. Using 0x40 correctly requests data from the sensor.

4fill in blank

hard

Fill both blanks to read two bytes from the sensor and combine them into a single integer.

Arduino

if (Wire.available()) {
  int highByte = Wire.read();
  int lowByte = Wire.[1]();
  int value = (highByte [2] 8) | lowByte;
}

Drag options to blanks, or click blank then click option'

Aread

B<<

C>>

D+

Attempts:

3 left

💡 Hint

Common Mistakes

Using Wire.available() instead of Wire.read() to get the byte.

Using right shift (>>) instead of left shift (<<).

Wire.read() reads the next byte. Shifting highByte left by 8 bits combines it with lowByte to form a 16-bit value.

5fill in blank

hard

Fill all three blanks to write a command byte 0x01 to the sensor at address 0x40 and end transmission.

Arduino

Wire.beginTransmission([1]);
Wire.[2](0x01);
Wire.[3]();

Drag options to blanks, or click blank then click option'

A0x20

Bwrite

CendTransmission

D0x40

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong sensor address 0x20.

Using print() instead of write() to send data.

Forgetting to end transmission.

beginTransmission starts communication with sensor at 0x40, write sends the command byte, and endTransmission ends the I2C communication.

Practice

1. What is the main purpose of the Wire.begin() function in Arduino when reading I2C sensor data?

easy

A. To initialize the I2C communication bus

B. To read data from the sensor

C. To write data to the sensor

D. To close the I2C communication

Solution

1. Step 1: Understand the role of Wire.begin()

   The Wire.begin() function sets up the Arduino to use the I2C bus, preparing it to communicate with I2C devices.

2. Step 2: Differentiate from other functions

   Reading or writing data happens after initialization; Wire.begin() does not perform these actions.

3. Final Answer:

   To initialize the I2C communication bus -> Option A

4. Quick Check:

   Wire.begin() initializes I2C [OK]

Hint: Remember: begin() always starts communication [OK]

Common Mistakes:

• Confusing Wire.begin() with reading or writing functions
• Thinking Wire.begin() sends or receives data
• Skipping Wire.begin() before communication

2. Which of the following is the correct syntax to request 2 bytes of data from an I2C device with address 0x40 using the Wire library?

easy

A. Wire.readFrom(0x40, 2);

B. Wire.request(0x40, 2);

C. Wire.requestFrom(0x40, 2);

D. Wire.getFrom(0x40, 2);

Solution

1. Step 1: Recall the correct Wire library function

   The function to request bytes from an I2C device is Wire.requestFrom(address, quantity).

2. Step 2: Match the syntax with the options

   Only Wire.requestFrom(0x40, 2); uses the correct function name and parameters.

3. Final Answer:

   Wire.requestFrom(0x40, 2); -> Option C

4. Quick Check:

   requestFrom(address, bytes) is correct [OK]

Hint: Use requestFrom() to get bytes from I2C device [OK]

Common Mistakes:

• Using incorrect function names like request() or readFrom()
• Mixing up parameter order
• Forgetting to specify the number of bytes

3. Consider this Arduino code snippet reading two bytes from an I2C sensor:

Wire.requestFrom(0x50, 2);
if (Wire.available() >= 2) {
  byte highByte = Wire.read();
  byte lowByte = Wire.read();
  int value = (highByte << 8) | lowByte;
  Serial.println(value);
}

If the sensor sends bytes 0x01 and 0xF4, what will be printed?

medium

A. 500

B. 400

C. 5000

D. 256

Solution

1. Step 1: Understand byte combination

   The code shifts the first byte (0x01) left by 8 bits and ORs it with the second byte (0xF4). This forms a 16-bit number.

2. Step 2: Calculate the combined value

   0x01 << 8 = 0x0100 (256 decimal), 0xF4 = 244 decimal, sum = 256 + 244 = 500.

3. Final Answer:

   500 -> Option A

4. Quick Check:

   (0x01 << 8) + 0xF4 = 500 [OK]

Hint: Shift high byte 8 bits left, then OR with low byte [OK]

Common Mistakes:

• Adding bytes without shifting
• Mixing byte order (low byte first)
• Printing raw bytes instead of combined value

4. This code tries to read a byte from an I2C sensor but does not work correctly:

Wire.begin();
Wire.beginTransmission(0x30);
Wire.write(0x00);
Wire.endTransmission();
byte data = Wire.read();
Serial.println(data);

What is the main problem?

medium

A. Wire.beginTransmission() address is wrong

B. Wire.read() is called without requesting data first

C. Wire.write() should be after Wire.read()

D. Wire.endTransmission() should be called twice

Solution

1. Step 1: Check the sequence of I2C functions

   The code sends a command but never calls Wire.requestFrom() to ask for data before reading.

2. Step 2: Understand Wire.read() usage

   Wire.read() only returns data after Wire.requestFrom() has been called and data is available.

3. Final Answer:

   Wire.read() is called without requesting data first -> Option B

4. Quick Check:

   Must requestFrom() before read() [OK]

Hint: Always requestFrom() before reading data [OK]

Common Mistakes:

• Calling Wire.read() without requestFrom()
• Misunderstanding beginTransmission() purpose
• Not checking if data is available before reading

5. You want to read temperature data from an I2C sensor that sends two bytes: the first byte is the integer part, the second byte is the fractional part in hundredths (e.g., 25 and 75 means 25.75°C). Which code snippet correctly reads and prints the temperature as a float?

hard

A. Wire.requestFrom(0x48, 2);
if (Wire.available() >= 2) {
byte intPart = Wire.read();
byte fracPart = Wire.read();
float temp = intPart + fracPart / 100;
Serial.println(temp);
}

B. Wire.requestFrom(0x48, 2);
if (Wire.available() >= 2) {
byte fracPart = Wire.read();
byte intPart = Wire.read();
float temp = intPart + fracPart / 100.0;
Serial.println(temp);
}

C. Wire.requestFrom(0x48, 2);
byte intPart = Wire.read();
byte fracPart = Wire.read();
float temp = intPart + fracPart * 100;
Serial.println(temp);

D. Wire.requestFrom(0x48, 2);
if (Wire.available() >= 2) {
byte intPart = Wire.read();
byte fracPart = Wire.read();
float temp = intPart + fracPart * 0.01;
Serial.println(temp);
}

Solution

1. Step 1: Confirm correct byte order and availability check

   The sensor sends integer part first, then fractional part. The code must check availability before reading both bytes.

2. Step 2: Calculate temperature correctly

   Fractional part is in hundredths, so divide by 100 or multiply by 0.01. Wire.requestFrom(0x48, 2); if (Wire.available() >= 2) { byte intPart = Wire.read(); byte fracPart = Wire.read(); float temp = intPart + fracPart * 0.01; Serial.println(temp); } uses fracPart * 0.01, which is correct and clear.

3. Final Answer:

   the snippet with fracPart * 0.01 -> Option D

4. Quick Check:

   Check availability, read int then frac, multiply frac by 0.01 [OK]

Hint: Check data availability and multiply fraction by 0.01 [OK]

Common Mistakes:

• Reading bytes in wrong order
• Not checking Wire.available() before reading
• Multiplying fraction by 100 instead of dividing