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Arduino Temperature Sensor

You’ll build a simple digital thermometer that measures ambient temperature using a temperature sensor (like the LM35, TMP36, or DHT11) and displays the reading via the Serial Monitor or LCD screen.

We’ll cover two main versions:

  1. Basic Version — Using an analog temperature sensor (LM35 or TMP36).

  2. Advanced Version — Using a digital sensor (DHT11 or DHT22) with humidity support.

Materials Needed

Component Quantity Description
Arduino Uno (or Nano/Mega) 1 The main microcontroller board
LM35 or TMP36 sensor 1 Analog temperature sensor
Breadboard 1 For easy circuit assembly
Jumper wires ~6 Male-to-male wires
USB cable 1 To connect Arduino to your computer
(Optional) 16×2 LCD Display 1 For local display
(Optional) 10kΩ Potentiometer 1 LCD contrast control

Step 1: Understand the Sensor

 LM35 Pinout

Pin Label Function
1 VCC +5V from Arduino
2 VOUT Analog output (connect to Arduino analog input)
3 GND Ground

The LM35 outputs 10 mV per °C.
So if the output voltage = 250 mV → temperature = 25°C.

Step 2: Wiring the LM35 to Arduino

Connections

LM35 Pin Connects To
VCC 5V on Arduino
GND GND on Arduino
VOUT A0 on Arduino

Circuit Diagram (Text Form)

[Arduino 5V] ---- [LM35 VCC]
[Arduino GND] ---- [LM35 GND]
[Arduino A0] ---- [LM35 OUT]

Step 3: Arduino Code (LM35 Version)

// Simple Temperature Sensor with LM35

const int sensorPin = A0; // LM35 connected to A0
float temperatureC;

void setup() {
Serial.begin(9600);
Serial.println(“LM35 Temperature Sensor”);
}

void loop() {
int sensorValue = analogRead(sensorPin); // Read analog value
float voltage = sensorValue * (5.0 / 1023.0); // Convert to voltage
temperatureC = voltage * 100; // 10mV per degree C (LM35)

Serial.print(“Temperature: “);
Serial.print(temperatureC);
Serial.println(” °C”);

delay(1000); // Update every second
}

Explanation

  • analogRead(A0): reads 0–1023 corresponding to 0–5V.

  • Voltage calculation: (value * 5.0) / 1023.0.

  • LM35 output scaling: 10 mV = 1°C → multiply voltage by 100.

Step 4: Viewing Data

  • Open Arduino IDE → Tools → Serial Monitor.

  • Set baud rate = 9600.

  • You’ll see continuous readings like:

    Temperature: 24.87 °C
    Temperature: 25.02 °C

Step 5: Calibration (Optional)

Real sensors may have small offsets.
You can adjust the output manually:

temperatureC = (voltage * 100) - 0.5; // Adjust by small offset

Compare readings with a known thermometer and tweak the offset until accurate.

Advanced: Using DHT11 / DHT22 (Digital Sensor)

Required Library

  • Install “DHT sensor library” by Adafruit from Arduino Library Manager.

Wiring (DHT11)

DHT11 Pin Connects To
VCC 5V
GND GND
DATA Digital Pin 2

Code (DHT11)

#include "DHT.h"

#define DHTPIN 2 // Data pin connected to digital pin 2
#define DHTTYPE DHT11 // or DHT22

DHT dht(DHTPIN, DHTTYPE);

void setup() {
Serial.begin(9600);
dht.begin();
}

void loop() {
float tempC = dht.readTemperature();
float humidity = dht.readHumidity();

if (isnan(tempC) || isnan(humidity)) {
Serial.println(“Failed to read from DHT sensor!”);
return;
}

Serial.print(“Temperature: “);
Serial.print(tempC);
Serial.print(” °C, Humidity: “);
Serial.print(humidity);
Serial.println(” %”);

delay(2000);
}

Step 6: (Optional) Display on LCD

If using a 16×2 LCD (I2C):

  1. Install “LiquidCrystal_I2C” library.

  2. Connect SDA → A4, SCL → A5.

  3. Example snippet:

#include <Wire.h>
#include <LiquidCrystal_I2C.h>LiquidCrystal_I2C lcd(0x27, 16, 2);

void setup() {
lcd.init();
lcd.backlight();
}

void loop() {
lcd.setCursor(0, 0);
lcd.print(“Temp: “);
lcd.print(temperatureC);
lcd.print(“C”);
}

Troubleshooting Guide

Issue Possible Cause Solution
No readings / 0°C Wrong wiring or pin Check sensor pins
Negative readings Wrong sensor type (TMP36 needs offset) Adjust formula
Unstable readings Noisy analog signal Add capacitor (0.1 µF) between VOUT & GND
“nan” or “Failed to read” DHT library issue Check sensor type & connections

Next Steps & Enhancements

  • Add OLED / LCD display for portable thermometer

  • Store data using SD card module

  • Upload readings to the cloud via ESP8266 / WiFi module

  • Use RGB LED to indicate temperature range (blue/cool, red/hot)

  • Build an IoT dashboard (ThingSpeak, Blynk, etc.).

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