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.

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

<syntaxhighlight lang="cpp"> // © 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

1. include <Wire.h>
2. 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);                       

} </syntaxhighlight>

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.