Experiment 2: Analog Sensor Interfacing (Temperature Sensor -LM35)

Experiment 2: Analog Sensor Interfacing (Temperature Sensor - LM35)

Objective

To interface the LM35 analog temperature sensor with Arduino and display the output on Serial Monitor or LCD.

Task

1. Connect LM35 to Arduino analog pin.
2. Write code to read and convert analog voltage to Celsius.
3. Display output on Serial Monitor or LCD.

⚠️ Disconnect your Arduino from the computer while making or removing component connections.

Circuit Diagram

Circuit Diagram

Board Connections

Board Connections

Connections

LM35 Pin	Arduino Pin
VCC (Pin 1)	5V
OUT (Pin 2)	A1
GND (Pin 3)	GND

Arduino UNO I2C Pins (for LCD)

Function	Arduino UNO Pin
SDA	A4
SCL	A5

Arduino Code

// © 2025, Cognifront. Member of The IoT Kits Family.

// Experiment 2: Analog Sensor Interfacing (Temperature Sensor -LM35)

// Define the analog input pin for LM35 temperature sensor
const int lm35_pin = A1;  

// Include required libraries for I2C communication and LCD
#include <Wire.h>                
#include <LiquidCrystal_I2C.h>    

// Initialize LCD at I2C address 0x27 with 16 columns and 2 rows
LiquidCrystal_I2C lcd(0x27, 16, 2);  

// Note: Arduino UNO connections for I2C:
// SDA -> A4
// SCL -> A5

void setup() {
  Serial.begin(9600);    // Start serial communication for debugging (9600 baud rate)
  lcd.init();            // Initialize the LCD
  lcd.backlight();       // Turn on the LCD backlight
}

void loop() {
  int temp_adc_val;      // Variable to store raw ADC reading from LM35
  float temp_val;        // Variable to store calculated temperature value in °C

  // Read analog value from LM35 temperature sensor
  temp_adc_val = analogRead(lm35_pin);

  // Convert ADC value (0–1023) to millivolts:
  // Each ADC step = 5V/1024 ≈ 4.88 mV
  temp_val = (temp_adc_val * 4.88);   // Convert to mV

  // LM35 provides 10mV per °C → convert mV to °C
  temp_val = (temp_val / 10);        

  // Print temperature value to Serial Monitor
  Serial.print("Temperature = ");
  Serial.print(temp_val);
  Serial.println(" *C");

  // Clear previous content on LCD before printing new data
  lcd.clear();

  // Display temperature on first line of LCD
  lcd.setCursor(0, 0);               // Set cursor to column 0, row 0
  lcd.print("Temp: ");               // Print label
  lcd.print(temp_val, 1);            // Print temperature with 1 decimal place
  lcd.print((char)223);              // Print degree (°) symbol
  lcd.print("C");                    // Print "C" for Celsius

  // Display sensor name on second line of LCD
  lcd.setCursor(0, 1);               
  lcd.print("LM35 Sensor");          

  // Wait 2 seconds before next reading
  delay(2000);                       
}

Notes

• The LM35 outputs 10mV per °C directly proportional to temperature.
• Make sure the LCD's I2C address (0x27 in this case) matches your module.
• For Arduino Uno, I2C pins are SDA → A4 and SCL → A5.

Observation

• The Serial Monitor displays the real-time temperature in Celsius.
• The LCD continuously updates and shows the measured temperature along with the label "LM35 Sensor".
• The temperature reading changes when the sensor is touched or exposed to a different heat source.

Conclusion

• The LM35 sensor was successfully interfaced with Arduino.
• The analog voltage output of the sensor was converted into a temperature value (°C).
• Data was accurately displayed on both the Serial Monitor and LCD, confirming correct sensor operation and code functionality.