Experiment 2: Analog Sensor Interfacing (Temperature Sensor -LM35) with ESP32

Objective

To interface the LM35 analog temperature sensor with ESP32 and display the output on Serial Monitor or LCD.

Task

Connect LM35 to ESP32 analog pin.
Write code to read and convert analog voltage to Celsius.
Display output on Serial Monitor or LCD.

⚠️ Disconnect your ESP32 from the computer while making or removing component connections.

Circuit & Board Connections

   
   
Circuit Diagram

   The complete connection diagram of ESP32-based setup.

   
   
Board Connections

   Actual board wiring layout showing sensor and module connections.

Connections

LM35 Pin	ESP32 Pin
VCC (Pin 1)	3.3V
OUT (Pin 2)	34
GND (Pin 3)	GND

ESP32 I2C Pins (for LCD)

Function	ESP32 UNO Pin
SDA	21
SCL	22

Important

Before uploading your ESP32 code, make sure you have installed the following libraries in the Arduino IDE: 1. Wire.h – For I²C communication between ESP32 and peripheral devices. 2. LiquidCrystal_I2C.h – For controlling LCD displays using the I²C interface.

✅ Install via (ZIP Method):

Sketch → Include Library → Add .ZIP Library → Select Downloaded .zip File → Open → Wait for “Library Installed” message

✅ Verify :

Sketch → Include Library → The included library name should be present

ESP32 Code

// © 2025, Cognifront. Member of The IoT Kits Family.
// Experiment 2: Analog Sensor Interfacing (Temperature Sensor - LM35)
/*
  🔌 LCD CONNECTIONS (16x2 I2C Display with ESP32)
  ------------------------------------------------
  LCD Pin     →  ESP32 Pin
  ----------------------------
  GND         →  GND
  VCC         →  3.3V or 5V  (depends on your module)
  SDA         →  GPIO21
  SCL         →  GPIO22

  ⚙️ NOTES:
  - Common I2C LCD addresses: 0x27 or 0x3F
  - If no text appears, change this line:
        LiquidCrystal_I2C lcd(0x27, 16, 2);
    to:
        LiquidCrystal_I2C lcd(0x3F, 16, 2);
  - LM35 temperature sensor input → GPIO34 (ADC input only)
*/
#include <Wire.h>
#include <LiquidCrystal_I2C.h>

const int lm35_pin = 34;   // LM35 -> GPIO34 (ADC input only)
LiquidCrystal_I2C lcd(0x27, 16, 2);

void setup() {
  Serial.begin(9600);
  Wire.begin(21, 22);   // SDA=21, SCL=22

  lcd.begin();
  lcd.backlight();

  Serial.println("System Initialized: LM35 Temperature Monitoring on ESP32");
}

void loop() {
  // Use ESP32 built-in calibrated ADC reading
  int voltage_mv = analogReadMilliVolts(lm35_pin);
  float temp_val = voltage_mv / 10.0;  // LM35 = 10 mV per °C

  Serial.print("Voltage (mV): ");
  Serial.print(voltage_mv);
  Serial.print(" -> Temp: ");
  Serial.print(temp_val, 1);
  Serial.println(" °C");

  lcd.clear();
  lcd.setCursor(0, 0);
  lcd.print("Temp: ");
  lcd.print(temp_val, 1);
  lcd.print((char)223);
  lcd.print("C");

  lcd.setCursor(0, 1);
  lcd.print("LM35 Sensor");

  delay(2000);
}

⚠️ If you encounter an error with lcd.begin(), try using lcd.init() instead — or vice versa.

 ⬇ Click Here to Download Code File
 

 (Contains ESP32 source code)
 

 
 

  Connect your ESP32 to your computer and upload the code make sure right port selected.

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 ESP32, 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 ESP32.
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.

Real Life Examples

Thermal Monitoring in CNC Machines: The LM35 sensor measures spindle or bearing temperatures to prevent overheating and ensure safe operation of high-speed cutting tools and mechanical components.