Reading temperature sensor (LM35, TMP36) in Arduino - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to read the analog value from the temperature sensor.

Arduino

int sensorPin = A0;
int sensorValue = [1];

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

AanalogRead(sensorPin)

BdigitalRead(sensorPin)

CpinMode(sensorPin, INPUT)

Ddelay(1000)

Attempts:

3 left

💡 Hint

Common Mistakes

Using digitalRead instead of analogRead

Trying to set pinMode inside reading

The analogRead() function reads the analog voltage from the sensor pin.

2fill in blank

medium

Complete the code to convert the analog value to voltage (assuming 5V reference).

Arduino

float voltage = sensorValue * [1] / 1023.0;

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

A10.0

B1.1

C5.0

D3.3

Attempts:

3 left

💡 Hint

Common Mistakes

Using 3.3V instead of 5.0V

Dividing by 1024 instead of 1023

The Arduino analog reference voltage is 5.0 volts, so multiply by 5.0 before dividing by 1023.

3fill in blank

hard

Fix the error in the code to calculate temperature in Celsius for LM35 sensor.

Arduino

float temperatureC = voltage [1] 0.01;

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

A/

B+

C*

D-

Attempts:

3 left

💡 Hint

Common Mistakes

Multiplying instead of dividing

Adding or subtracting instead of dividing

The LM35 outputs 10mV (0.01V) per degree Celsius, so divide voltage by 0.01 to get temperature.

4fill in blank

hard

Fill both blanks to calculate temperature in Celsius for TMP36 sensor.

Arduino

float temperatureC = (voltage [1] 0.5) [2] 0.01;

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

A-

B/

C*

Attempts:

3 left

💡 Hint

Common Mistakes

Adding 0.5 instead of subtracting

Multiplying instead of dividing

The TMP36 sensor outputs 0.5V at 0°C and 10mV/°C, so subtract 0.5V then divide by 0.01 to get Celsius.

5fill in blank

hard

Fill the blanks to print the temperature in Celsius with one decimal place.

Arduino

Serial.print("Temperature: ");
Serial.print([1], [2]);
Serial.println(" C");

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

AtemperatureC

B1

CtemperatureF

D2

Attempts:

3 left

💡 Hint

Common Mistakes

Printing Fahrenheit variable instead of Celsius

Using wrong decimal places

Use Serial.print() with the temperature variable and specify 1 decimal place for clarity.

Practice

1. What does the analogRead() function do when reading from an LM35 temperature sensor?

easy

A. It sets the sensor's output voltage to a fixed value.

B. It converts the temperature directly to Celsius.

C. It sends data to the sensor to start measuring temperature.

D. It reads the voltage level from the sensor's analog output pin.

Solution

1. Step 1: Understand analogRead() function

   The analogRead() function reads the voltage level on an analog pin and returns a number between 0 and 1023 representing that voltage.

2. Step 2: Relate to LM35 sensor output

   The LM35 outputs an analog voltage proportional to temperature, so analogRead() reads this voltage level.

3. Final Answer:

   It reads the voltage level from the sensor's analog output pin. -> Option D

4. Quick Check:

   analogRead() reads voltage level = A [OK]

Hint: Remember: analogRead() reads voltage, not temperature directly [OK]

Common Mistakes:

• Thinking analogRead() converts voltage to temperature
• Assuming analogRead() sends commands to sensor
• Confusing analogRead() with digitalRead()

2. Which of the following is the correct way to convert the analog reading from an LM35 sensor to voltage in Arduino code?

easy

A. float voltage = analogRead(sensorPin) / 5.0;

B. float voltage = analogRead(sensorPin) * 1023.0 / 5.0;

C. float voltage = analogRead(sensorPin) * (5.0 / 1023.0);

D. float voltage = analogRead(sensorPin) * 5.0;

Solution

1. Step 1: Understand analog to voltage conversion

   The analog reading ranges from 0 to 1023 for 0 to 5 volts. To get voltage, multiply reading by (5.0 / 1023.0).

2. Step 2: Check each option

   float voltage = analogRead(sensorPin) * (5.0 / 1023.0); correctly applies the formula. Others either divide incorrectly or multiply by wrong factors.

3. Final Answer:

   float voltage = analogRead(sensorPin) * (5.0 / 1023.0); -> Option C

4. Quick Check:

   Voltage = reading * (5/1023) [OK]

Hint: Use (5.0 / 1023.0) to convert analog reading to voltage [OK]

Common Mistakes:

• Dividing by 5 instead of multiplying
• Using 1024 instead of 1023 in denominator
• Multiplying by 5 without dividing by 1023

3. What will be the output on the Serial Monitor if the following Arduino code reads an analog value of 250 from an LM35 sensor?

int sensorPin = A0;
int reading = 250;
float voltage = reading * (5.0 / 1023.0);
float temperatureC = voltage * 100;
Serial.println(temperatureC);

medium

A. 122.0

B. 12.2

C. 0.25

D. 1.22

Solution

1. Step 1: Calculate voltage from reading

   voltage = 250 * (5.0 / 1023.0) ≈ 1.22 volts.

2. Step 2: Calculate temperature in Celsius

   temperatureC = 1.22 * 100 ≈ 122 °C. Serial.println displays approximately 122.19, closest to 122.0.

3. Final Answer:

   122.0 -> Option A

4. Quick Check:

   Voltage ≈1.22V, Temp = voltage*100 = 122 [OK]

Hint: Multiply voltage by 100 to get Celsius for LM35 [OK]

Common Mistakes:

• Forgetting to multiply voltage by 100
• Using wrong analog to voltage conversion
• Confusing TMP36 formula with LM35

4. Identify the error in this Arduino code snippet for reading TMP36 temperature sensor:

int sensorPin = A0;
int reading = analogRead(sensorPin);
float voltage = reading / 1023 * 5.0;
float temperatureC = (voltage - 0.5) * 100;
Serial.println(temperatureC);

medium

A. The voltage calculation divides before multiplying, causing integer division error.

B. The sensorPin should be declared as float, not int.

C. The temperature formula is incorrect for TMP36 sensor.

D. Serial.println() cannot print float values.

Solution

1. Step 1: Analyze voltage calculation

   reading / 1023 * 5.0 uses left-to-right precedence: first reading / 1023 (int / int = integer division, truncates), then * 5.0, yielding wrong voltage.

2. Step 2: Rule out other options

   A: Formula (voltage - 0.5)*100 correct for TMP36. B: Pin declaration int is fine. D: Serial.println prints floats fine.

3. Final Answer:

   The voltage calculation divides before multiplying, causing integer division error. -> Option A

4. Quick Check:

   Use float divisor to avoid integer division [OK]

Hint: Use float numbers in division to avoid integer division [OK]

Common Mistakes:

• Using integer 1023 instead of float 1023.0
• Misunderstanding operator precedence
• Thinking Serial.println() can't print floats

5. You want to read temperature from a TMP36 sensor connected to analog pin A1 and print the temperature in Celsius every second. Which Arduino code snippet correctly implements this?

hard

A. int sensorPin = A1;
void loop() {
int reading = analogRead(sensorPin);
float voltage = reading / 1023 * 5;
float temperatureC = voltage * 100;
Serial.println(temperatureC);
delay(1000);
}

B. int sensorPin = A1;
void loop() {
int reading = analogRead(sensorPin);
float voltage = reading * (5.0 / 1023.0);
float temperatureC = (voltage - 0.5) * 100;
Serial.println(temperatureC);
delay(1000);
}

C. int sensorPin = A1;
void loop() {
int reading = analogRead(sensorPin);
float voltage = reading * (5 / 1023);
float temperatureC = (voltage - 0.5) * 100;
Serial.println(temperatureC);
delay(1000);
}

D. int sensorPin = A1;
void loop() {
int reading = analogRead(sensorPin);
float voltage = reading * (5.0 / 1023.0);
float temperatureC = voltage * 100;
Serial.println(temperatureC);
delay(1000);
}

Solution

1. Step 1: Confirm TMP36 formula

   Temperature = (voltage - 0.5) * 100.

2. Step 2: Check voltage conversion

   Correct: reading * (5.0 / 1023.0). Avoid integer division like reading / 1023 * 5 (truncates) or 5 / 1023 (zero).

3. Step 3: Verify loop structure

   A1 pin, analogRead, Serial.println, delay(1000) must all align with correct math.

4. Final Answer:

   int sensorPin = A1; void loop() { int reading = analogRead(sensorPin); float voltage = reading * (5.0 / 1023.0); float temperatureC = (voltage - 0.5) * 100; Serial.println(temperatureC); delay(1000); } -> Option B

5. Quick Check:

   TMP36 temp = (voltage - 0.5)*100 with float math [OK]

Hint: Use (voltage - 0.5)*100 for TMP36 temperature [OK]

Common Mistakes:

• Using LM35 formula for TMP36 sensor
• Integer division in voltage calculation
• Using integer math like 5 / 1023 resulting in zero