How to Build a Temperature-Based LED Bar with TMP36 and Arduino

How to Build a Temperature-Based LED Bar with TMP36 and Arduino

In this project, we’ll use a TMP36 temperature sensor and an Arduino to light up a row of LEDs based on the ambient temperature. As the temperature increases, more LEDs will light up from left to right, just like a temperature meter.

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Components Required

• Arduino Uno Starter Kit
• Bread Board
• Jumper Wires
• 5mm LEDs Assortment Pack
• Resistors ( 220 ohms recommended)
• TM36 Temperature Sensor

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TMP36 Pinout and Wiring

Facing the flat side of the TMP36 with the text facing you:

TMP36 Pin	Connects to	Description
1 (VCC)	5V	Power supply
2 (VOUT)	A0	Analog output to Arduino
3 (GND)	GND	Ground

LEDs: Connect 6 LEDs to Arduino digital pins D2 through D7, each in series with a 220Ω resistor.

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Arduino Code

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const int tempPin = A0;
const int ledPins[] = {2, 3, 4, 5, 6, 7};
const int ledCount = 6;

void setup() {
  for (int i = 0; i < ledCount; i++) {
    pinMode(ledPins[i], OUTPUT);
  }
}

void loop() {
  int sensorValue = analogRead(tempPin);
  float voltage = sensorValue * (5.0 / 1023.0); // Convert analog reading to voltage
  float temperatureC = (voltage - 0.5) * 100.0; // TMP36: 10mV per degree with 500mV offset

  // Map temperature range (20–40°C) to number of LEDs to turn on (0–6)
  int level = map(temperatureC, 20, 40, 0, ledCount);
  level = constrain(level, 0, ledCount);

  // Light up LEDs according to temperature level
  for (int i = 0; i < ledCount; i++) {
    digitalWrite(ledPins[i], i < level ? HIGH : LOW);
  }

  delay(300); // Short delay to stabilize readings
}

Visual Temperature Bar with TMP36

This standalone project turns an analog temperature sensor (TMP36) into a simple LED thermometer. It’s ideal for learning how to convert analog input into real-world feedback.

Code Explanation

const int tempPin = A0;
const int ledPins[] = {2, 3, 4, 5, 6, 7};
const int ledCount = 6;

void setup() {
  for (int i = 0; i < ledCount; i++) {
    pinMode(ledPins[i], OUTPUT);
  }
}

void loop() {
  int sensorValue = analogRead(tempPin);
  float voltage = sensorValue * (5.0 / 1023.0); // Convert analog reading to voltage
  float temperatureC = (voltage - 0.5) * 100.0; // TMP36: 10mV per degree with 500mV offset

  int level = map(temperatureC, 20, 40, 0, ledCount);
  level = constrain(level, 0, ledCount);

  for (int i = 0; i < ledCount; i++) {
    digitalWrite(ledPins[i], i < level ? HIGH : LOW);
  }

  delay(300);
}

How It Works

– The TMP36 sensor gives an analog voltage that corresponds to temperature.
– The formula (voltage - 0.5) * 100 converts that voltage to Celsius.
– The temperature is then mapped from 20°C–40°C into 0–6 LED levels.
– Based on the current temperature, a corresponding number of LEDs light up to create a bar-style indicator.

Why It’s Cool

This project is beginner-friendly, highly visual, and easily extendable. You can add an OLED display, buzzers, or even WiFi integration later.

How It Works

• The TMP36 sensor provides an analog voltage based on the ambient temperature. At 0°C, the output is around 0.5V. Each 1°C adds 10mV.
• Arduino reads this analog signal from pin A0. The voltage is then converted to degrees Celsius using the formula: (voltage - 0.5) * 100.
• The temperature is mapped from a range (e.g., 20°C to 40°C) to how many LEDs should light up (from 0 to 6).
• For example:
  • At 0°C → 0 LEDs on
  • At 50°C → ~3 LEDs on
  • At 100°C → All 6 LEDs on
• This creates a simple visual feedback system showing how hot it is using lights instead of a number.

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Optional Upgrades

• Replace the LEDs with RGB LEDs and fade colors based on temperature.
• Add a buzzer to beep when temperature exceeds a certain threshold.
• Display the temperature on an LCD or OLED.
• Change LED colors based on temperature zones: green (cool), yellow (warm), red (hot).

🔧 Recommended Arduino Starter Kits for Beginners

If you’re just getting started with Arduino, these beginner-friendly kits will help you learn faster and avoid the headache of missing parts. They all include essential components like LEDs, resistors, jumper wires, and an Arduino-compatible board.

• Arduino Official Starter Kit
  Includes a genuine Arduino UNO board, project book, and components for 15+ tutorials.
  👉 Check it on Amazon


• Elegoo UNO R3 Super Starter Kit
  Affordable and packed with sensors, LEDs, motors, and wires — great value.
  👉 View the Elegoo Kit


• Freenove Ultimate Starter Kit
  Includes 200+ components, an Arduino-compatible board, and 50+ example projects.
  👉 See the Freenove Kit

💡 Tip: Choose a kit with a good variety of components so you can build multiple projects without buying extra parts later.

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