Arduino LED Temperature Indicator





Introduction: Arduino LED Temperature Indicator

This design is made to keep track of the temperature in a room.

You give it the parameters you want and it will light a blue LED if it is too cold, a red LED if it's too hot, and a green one if it's just right.

Step 1: Get Parts

You will need:

  • Arduino board
  • Breadboard
  • Jumper wires
  • 3 220Ω resistors (red-red-brown)
  • 3 LEDs (colors of your choice)
  • A temperature sensor (mine is an LM35, but most should work)

Buy specialty parts:

Temp sensor -

Step 2: Put Parts in Place

Not much explaining to do on this step, just follow the picture.

Step 3: Wire It Up

Wire it up:

>Red LED goes to digital pin 4 through one of the resistors, and ground

>Green LED goes to digital pin 3 though a resistor, and ground

>Blue LED goes to digital pin 2 through a resistor, and ground

>Pin one (the pin on the left) of the temperature sensor goes to 5v

>Pin two (the pin in the middle) of the temperature sensor goes to analog pin A2

>pin three (the pin on the right) of the temperature sensor goes to ground

Step 4: Coding

Connect your Arduino to your computer and upload this code:

const int hot = 87; //set hot parameter
const int cold = 75; //set cold parameter
void setup() {
pinMode(A2, INPUT); //sensor
pinMode(2, OUTPUT); //blue
pinMode(3, OUTPUT); //green
pinMode(4, OUTPUT); //red
void loop() {
int sensor = analogRead(A2);
float voltage = (sensor / 1024.0) * 5.0;
float tempC = (voltage - .5) * 100;
float tempF = (tempC * 1.8) + 32;
Serial.print("temp: ");
if (tempF < cold) { //cold
digitalWrite(2, HIGH);
digitalWrite(3, LOW);
digitalWrite(4, LOW);
Serial.println(" It's Cold.");
else if (tempF >= hot) { //hot
digitalWrite(2, LOW);
digitalWrite(3, LOW);
digitalWrite(4, HIGH);
Serial.println(" It's Hot.");
else { //fine
digitalWrite(2, LOW);
digitalWrite(3, HIGH);
digitalWrite(4, LOW);
Serial.println(" It's Fine.");

Open the Serial Monitor in the Arduino program, and watch what happens!

Remember to look at the project's web site:

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1 Questions

what if I wanted that in celsius? :)

okay I figured it out!


I had a few complications at first with this project, but eventually I figured them out and this is a very cool project, you did a good job designing it!