How to Read Temperature Using LM35 Sensor in Arduino

To read temperature using an LM35 sensor in Arduino, connect the sensor's output to an analog pin and use analogRead() to get the voltage value. Convert this value to temperature by multiplying the voltage by 100 because LM35 outputs 10mV per °C.

Syntax

The basic syntax to read temperature from an LM35 sensor involves reading the analog input and converting it to Celsius.

• analogRead(pin): Reads the voltage from the sensor connected to the specified analog pin.
• Conversion formula: temperature = (analogValue * (5.0 / 1023.0)) * 100 converts the analog reading to temperature in Celsius.

arduino

int sensorPin = A0;  // Analog pin connected to LM35
int analogValue = analogRead(sensorPin);  // Read analog value
float voltage = analogValue * (5.0 / 1023.0);  // Convert to voltage
float temperatureC = voltage * 100;  // Convert voltage to temperature in Celsius;

Example

This example reads the temperature from the LM35 sensor connected to analog pin A0 and prints the temperature in Celsius to the Serial Monitor every second.

arduino

const int sensorPin = A0;

void setup() {
  Serial.begin(9600);  // Start serial communication
}

void loop() {
  int analogValue = analogRead(sensorPin);  // Read sensor value
  float voltage = analogValue * (5.0 / 1023.0);  // Convert to voltage
  float temperatureC = voltage * 100;  // Convert voltage to temperature

  Serial.print("Temperature: ");
  Serial.print(temperatureC);
  Serial.println(" °C");

  delay(1000);  // Wait 1 second before next reading
}

Output

Temperature: 23.45 °C
Temperature: 23.50 °C
Temperature: 23.48 °C
...

Common Pitfalls

• Incorrect pin connection: Make sure the LM35 output pin is connected to an analog input pin, not a digital pin.
• Wrong voltage reference: The Arduino analog input reads 0-5V by default; if using a different reference voltage, adjust the formula accordingly.
• Ignoring sensor power: LM35 needs 5V and ground connections; missing these will give wrong readings.
• Not converting analog value properly: Forgetting to scale the analog reading to voltage and then to temperature causes incorrect results.

arduino

/* Wrong way: Using digitalRead instead of analogRead */
int sensorPin = A0;
int value = digitalRead(sensorPin);  // WRONG: LM35 output is analog

/* Right way: Use analogRead and convert */
int analogValue = analogRead(sensorPin);
float voltage = analogValue * (5.0 / 1023.0);
float temperatureC = voltage * 100;

Quick Reference

Step	Description
Connect LM35 output to Arduino analog pin (e.g., A0)	Read analog voltage from sensor
Use analogRead(pin) to get sensor value	Returns 0-1023 corresponding to 0-5V
Convert analog value to voltage	voltage = analogValue * (5.0 / 1023.0)
Convert voltage to temperature	temperatureC = voltage * 100 (°C)
Print or use temperature value in your program	Use Serial.print() or other output

Key Takeaways

Connect LM35 output to an Arduino analog pin and power it with 5V and ground.

Use analogRead() to get the sensor's voltage reading.

Convert the analog reading to voltage, then multiply by 100 to get temperature in Celsius.

Always verify wiring and use the correct conversion formula for accurate temperature readings.

Print temperature values to Serial Monitor for easy debugging.