How to Build a Digital Temperature Monitor with LM35 and Arduino (Step-by-Step Guide)

Learn how to build a digital temperature monitoring system using the LM35 sensor and Arduino. Includes circuit diagram, Arduino code, real-world applications, and troubleshooting tips.

---

Introduction

Monitoring environmental temperature in real-time is a fundamental requirement across many applications. These range from home automation systems to industrial processes and agricultural setups. In this project, you will learn how to build a Digital Temperature Monitor using LM35 and Arduino UNO.

The LM35 is a precision temperature sensor that offers a linear output directly proportional to the temperature in Celsius. It’s reliable, inexpensive, and extremely easy to use—making it ideal for educational and prototyping purposes.

What the Project Does

This Arduino-based system reads the analog voltage from the LM35 temperature sensor. It converts it into Celsius. Then, it displays the temperature data on the Serial Monitor or an optional LCD screen.

Real-World Use Cases

• Smart Thermostats
• Greenhouse Temperature Control
• Server Room Monitoring
• Weather Stations
• Appliance Overheating Alerts

Skill Level

Beginner to Intermediate

Expected Outcome

By the end of this tutorial, you’ll understand:

• How to wire and interface the LM35 sensor with Arduino
• Analog-to-digital conversion (ADC) in Arduino
• How to calculate accurate temperature from the sensor’s output
• Displaying real-time data on the Serial Monitor or LCD

---

Components Required

Quantity	Component	Description	Buy Link
1	Arduino UNO with cable	Main microcontroller board	Buy on Elecsynergy
1	LM35 Temperature Sensor	Analog temperature sensor, output in millivolts/°C	Buy on Elecsynergy
1	Breadboard	For creating the prototype circuit	Buy on Elecsynergy
3	Jumper Wires (M-M)	Male-to-male wires for circuit connection	Buy on Elecsynergy
Optional	16×2 LCD Display	To display temperature in real-time	Buy on Elecsynergy

---

Circuit Diagram + Explanation

Basic Connection (Serial Monitor Only)

• LM35 VCC → 5V on Arduino
• LM35 GND → GND on Arduino
• LM35 OUT → A0 (Analog pin) on Arduino UNO

Optional LCD Wiring (16×2 LCD)

• LCD RS → Pin 12
• LCD EN → Pin 11
• LCD D4-D7 → Pins 5-2 respectively
• Contrast pin via 10K pot

⚠️ Note: For accurate readings, keep sensor wires short and avoid electrical noise.

Visual Schematic

A Fritzing-based diagram will be inserted here showing both LCD and non-LCD versions.

---

Arduino Code – Line-by-Line Explanation

Basic Code for Serial Monitor Display:

const int sensor = A0;  // Assigning analog pin A5 to variable 'sensor'

float tempc;  //variable to store temperature in degree Celsius

float tempf;  //variable to store temperature in Fahreinheit

float vout;  //temporary variable to hold sensor reading

void setup() {

  pinMode(sensor, INPUT);  // Configuring sensor pin as input

  Serial.begin(9600);
}

void loop() {
  vout = analogRead(sensor);  //Reading the value from sensor

  vout = (vout * 500) / 1023;

  tempc = vout;  // Storing value in Degree Celsius

  tempf = (vout * 1.8) + 32;  // Converting to Fahrenheit

  Serial.print("in DegreeC=");

  Serial.print("\t");

  Serial.print(tempc);

  Serial.print(" ");

  Serial.print("in Fahrenheit=");

  Serial.print("\t");

  Serial.print(tempf);

  Serial.println();

  delay(500);  //Delay of 1 second for ease of viewing 
}

Explanation:

• analogRead(A0) reads the analog voltage (0–1023).
• (value * 5.0/1024) converts ADC to voltage.
• Multiplying by 100 converts millivolts to Celsius (10mV per °C).

Code to Display Temperature on 16×2 lCD

#include <LiquidCrystal.h>

// Define LCD pins in 4-bit mode
const int rs = 12, en = 11, d4 = 5, d5 = 4, d6 = 3, d7 = 2;
LiquidCrystal lcd(rs, en, d4, d5, d6, d7);

const int tempSensorPin = A0;
float tempc;  //variable to store temperature in degree Celsius

float tempf;  //variable to store temperature in Fahreinheit

float vout;  //temporary variable to hold sensor reading

void setup() {
  lcd.begin(16, 2);
  lcd.print("Temp:");
}

void loop() {
vout = analogRead(tempSensorPin);  //Reading the value from sensor

  vout = (vout * 500) / 1023;

  tempc = vout;  // Storing value in Degree Celsius

  tempf = (vout * 1.8) + 32;  // Converting to Fahrenheit

  lcd.setCursor(0, 1);
  lcd.print("Temp:");
  lcd.print(tempc);
  lcd.println(" C");
  delay(1000);
  lcd.clear();
}

---

Working Explanation

How the Process Operates:

1. The LM35 outputs 10 mV per degree Celsius.
2. Arduino reads this analog voltage through pin A0.
3. The value is converted to Celsius using the given formula.
4. The temperature is printed on the Serial Monitor or LCD.

The sensor works best in the range of 2°C to 150°C with an accuracy of ±0.5°C at room temperature.

Optional LCD Version: You can include the LiquidCrystal library and update the temperature data on a 16×2 character LCD.

---

Demo / Output Preview

📸 What You’ll See:

• Temperature readings updating every second.
• Optional: Live reading on 16×2 LCD.

---

Troubleshooting & Tips

• Wrong or fluctuating values?
  • Ensure tight wiring.
  • Use shielded cables or twist the data line if needed.
• Incorrect readings?
  • Check if sensor is connected correctly.
  • Use a multimeter to verify voltage at OUT pin.
• Sensor heating up?
  • Disconnect immediately — double-check VCC/GND pins.
• Using with LCD?
  • Make sure to include LiquidCrystal library.
  • Adjust potentiometer to improve LCD contrast.

---

Project Expansion Ideas

1. High Temperature Alert System

Add a buzzer or LED to alert when temperature exceeds a threshold.

2. Temperature Logging

Interface with SD Card Module to log real-time data.

3. Remote Temperature Monitoring

Send temperature data wirelessly using ESP8266/ESP32.

4. IoT Dashboard Integration

Push real-time data to platforms like ThingSpeak, Blynk, or Adafruit IO.

5. Fan or Relay Control

Automatically control cooling devices or fans based on temperature thresholds.

---

Conclusion

Congratulations! You’ve successfully built a Digital Temperature Monitor using Arduino and LM35. This is a highly practical project with immense real-world utility. It teaches you how to read analog sensors. You also learn how to process, display, and act upon environmental data.

✅ Challenge: Try integrating this system into a weather station or home automation hub. Can you make it Wi-Fi enabled?

Keep learning, keep innovating — and don’t forget to share your project with the community!

---

🛒 Buy the Complete Kit

Order from Elecsynergy

---

#LM35Arduino #TemperatureMonitor #ArduinoProjects #EmbeddedSystems #IoTProjects #Elecsynergy #InnovateYourself #ArduinoSensors #SmartAutomation #DigitalTemperatureMonitor