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LM35
CIRCUIT
LM35 TEMPERATURE FORMULA

Published April 18, 2021 © GPL3+

Digital thermometer using LM35 and arduino

Read the temperature fast with accuracy

IntermediateFull instructions provided3 hours11,668

Things used in this project

Hardware components

5 mm LED: Red

5 mm LED: Green

Rotary potentiometer (generic)

Jumper wires (generic)

Breadboard (generic)

Resistor 220 ohm

Arduino UNO

Arduino LM35

Software apps and online services

Arduino IDE

Story

This project is a simple thermometer which is easy to use and provides accurate results.

1)When the temperature is more than 35 degree celsius, the green led glows.

2)When the temperature is less than 35 degree celsius, the red led glows.

3)The 10K ohm potentiometer is used to set contrast of 16x2 LCD screen.

The main component used here is the temperature sensor (LM35).

LM35

LM35 is a temperature sensor that provides analog signal as its output which is linearly proportional to the temperature in degree celsius.

LM35 has three pins:

PIN 1 : Vcc, it is the input pin (5v)

PIN 2 : Vout, we get output (it should be connected to the analog pin of arduino)

PIN 3 : GND, it is used for ground

Img src = https://deepbluembedded.com/temperature-sensor-lm35-interfacing-with-pic-microcontrollers/

CIRCUIT

Here I have used arduino and little bit of c programming for this project. Make the connections as given below:

https://www.tinkercad.com/things/ddvnnsV6y88

Select the board in IDE as "Arduino Uno" and upload the code given.

If the code fails to upload, please check your USB or try re-plugging it.

LM35 TEMPERATURE FORMULA

LM35 output voltage is directly proportional to celsius and 10 milli volts represents 1 degree celsius.

Note: LM35 can measure from -50 to 150 degree celsius.

Arduino's analog pin resolution is from 0-1023, ie at +5v input it counts to 1023.

LM35 max input is 1500 milli volts (as max temperature is 150 degree celsius) or 1.5v (max output voltage).

So at 1.5v, analog pin count is equal to (1.5/5)*1023 = 306.9.

Now LM35 new resolution equals 306.9/150 = 2.046. This analog pin counts 2.046, equals to 1 degree change in celsius temperature of LM35.

FINAL EXECUTION

After uploading the code to the arduino, make sure that the circuit connections are correct.

Here I have used 5V of arduino to power up the sensor(LM35) and the LCD. You can also use a seperate 5V supply from a battery.

When the temperature is more than 35 degree celsius the green led glows as shown below:

When the temperature is below 35 degree celsius, the red led glows as shown below:

You can also the simulation online : https://www.tinkercad.com/things/ddvnnsV6y88

Digital_thermometer code

#include <LiquidCrystal.h>
LiquidCrystal lcd(8,9,10,11,12,13);
#define LM35_sensor A0
byte degree[8]={
  0b00011,
  0b00011,
  0b00000,
  0b00000,
  0b00000,
  0b00000,
  0b00000,
  0b00000
};


int LEDR = 5;
int LEDG = 7;


void setup() {
  // put your setup code here, to run once:
pinMode(LEDR,OUTPUT);
pinMode(LEDG,OUTPUT);

lcd.begin(16,2);
lcd.createChar(1, degree);
lcd.setCursor(0,0);
lcd.print(" DIGITAL ");
lcd.setCursor(0,1);
lcd.print(" THERMOMETER ");
delay(2800);
lcd.clear();

}

void loop() {
  
  // temperature:
  
  float analog_read = analogRead(LM35_sensor);
  float temp = analog_read/2.046 ;
  delay(10);
  
//lcd display:

  lcd.clear();
  lcd.setCursor(2,0);
  lcd.print("TEMPERATURE");
  lcd.setCursor(4,1);
  lcd.print(temp);
  lcd.write(1);// READ ASCII VALUE
  lcd.print("C");
  delay(1000);
  
  //led :

  if(temp<35)
  {

     digitalWrite(LEDG,LOW);
    digitalWrite(LEDR,HIGH);

 
  
  
  }
  else{
     digitalWrite(LEDR,LOW);
     digitalWrite(LEDG,HIGH);
 
  
  }

  

}

Credits

Aarush Sood

5 projects • 10 followers

Technology enthusiast , ECE graduate from India. An electronics hobbyist who loves working with arduino's and esp's.

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Digital thermometer using LM35 and arduino

Digital thermometer using LM35 and arduino

Things used in this project

Hardware components

Software apps and online services

Story

LM35

CIRCUIT

LM35 TEMPERATURE FORMULA

Code

Digital_thermometer code

Credits

Aarush Sood

Comments

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