Basic Electronics for Beginners: Arduino Digital Thermometer

1. Introduction

Temperature measurement is one of the most common and important applications in electronics. In this project, we build a Digital Thermometer using Arduino and LM35 sensor, which can measure temperature accurately and display it in real time.

The LM35 sensor provides an output voltage directly proportional to temperature in Celsius, making it very easy to interface with Arduino without complex calculations.

2. Components Required

Arduino Uno / Nano
LM35 Temperature Sensor
16x2 LCD Display (optional but recommended)
10k Potentiometer (for LCD contrast)
Breadboard
Jumper Wires
USB Cable / Power Supply

3. Circuit and Connections

Pinout Diagram of Arduino Uno

LM35 Pinout Diagram
Pin-out Diagram 16X2 LCD
LM35 Connections

VCC → 5V (Arduino)
GND → GND
OUT → A0 (Arduino)

LCD Connections (Optional)

VSS → GND
VDD → 5V
V0 → Middle pin of potentiometer
RS → Pin 7
EN → Pin 6
D4 → Pin 5
D5 → Pin 4
D6 → Pin 3
D7 → Pin 2
RW → GND

4. Detailed Step By Step Circuit Working

The LM35 sensor senses ambient temperature.
It outputs an analog voltage (10mV per °C).
Arduino reads this voltage using analog pin A0.
The analog value is converted into temperature in Celsius.
The calculated temperature is:
- Displayed on Serial Monitor
- Shown on LCD (if connected)

5. Libraries to be Included

For LCD display:


#include <LiquidCrystal.h>

6. Code


#include <LiquidCrystal.h>

LiquidCrystal lcd(7, 6, 5, 4, 3, 2);

int sensorPin = A0;
float temperature;

void setup() {
  lcd.begin(16, 2);
  Serial.begin(9600);
}

void loop() {
  int reading = analogRead(sensorPin);
  
  float voltage = reading * (5.0 / 1023.0);
  temperature = voltage * 100; // LM35 conversion

  Serial.print("Temperature: ");
  Serial.print(temperature);
  Serial.println(" C");

  lcd.setCursor(0, 0);
  lcd.print("Temp: ");
  lcd.print(temperature);
  lcd.print(" C");

  delay(1000);
}

7. Detailed Step By Step Code Working

analogRead(A0) reads sensor value (0–1023)
Convert to voltage using:
```
voltage = reading × (5.0 / 1023.0)
```
LM35 gives 10mV per °C, so:
```
temperature = voltage × 100
```
Data is displayed on:
- Serial Monitor
- LCD Display
Loop runs every 1 second

8. Testing and Calibration

Upload the code to Arduino
Open Serial Monitor
Observe temperature values
Compare with room thermometer
Slight variations are normal
Avoid touching sensor directly (body heat affects reading)

9. Applications

Room temperature monitoring
Weather stations
Industrial temperature measurement
HVAC systems
Laboratory instruments

10. Advantages

Simple and low cost
No calibration required (factory calibrated)
Direct Celsius output
Easy interfacing with Arduino

11. Disadvantages

Limited temperature range
Not waterproof
Less accurate than digital sensors (like DHT22)
Affected by noise if wiring is long

12. Future Improvements

Add IoT monitoring (ESP8266/ESP32)
Use OLED display for better UI
Add data logging (SD card)
Use multiple sensors for area monitoring

Arduino Digital Thermometer