Assignment Goal

For Week 4, I worked on embedded programming using an Arduino Uno R3 starter kit. I built a small automatic cooling system. The idea was simple: when the temperature sensor gets warm, the red LED turns on and the fan motor turns on. When the sensor cools down, the fan turns off and the green LED turns on.

This project helped me see how software and hardware work together. The Arduino reads an input from the TMP36 temperature sensor, makes a decision in the code, and then controls output devices like LEDs, a motor, and an LCD screen.

Components Used

• Arduino Uno R3
• TMP36 temperature sensor
• Red LED
• Green LED
• Current limiting resistors
• Small DC motor/fan
• 9V battery connector
• IRF520 MOSFET motor driver module
• 16x2 LCD display
• Potentiometer for LCD contrast
• Breadboard and jumper wires

Microcontroller and Sensor Information

The Arduino Uno R3 is based on the ATmega328P microcontroller. It operates at 5V, has 14 digital input/output pins, 6 analog input pins, and runs at 16 MHz. This made it a good board for this project because I needed analog input for the TMP36 sensor and digital output pins for the LEDs, LCD, and motor control.

The TMP36 is an analog temperature sensor. It outputs a voltage that changes with temperature. The Arduino reads that voltage on an analog pin and the code converts the reading into degrees Celsius. The important part I had to understand was that the sensor reading is not just a temperature number right away. It has to be converted from analog value, to voltage, and then to temperature.

Project Images

These pictures show the process of wiring, testing, programming, and debugging the embedded cooling system.

How the Code Works

The code starts by loading the LiquidCrystal library so the Arduino can control the LCD screen. Then the code assigns pin numbers for the TMP36 temperature sensor, red LED, green LED, and fan. In the setup section, the LCD is started and the LED and fan pins are set as outputs.

Inside the main loop, the Arduino reads the TMP36 sensor using analogRead(). The analog reading is converted into voltage. Then the voltage is converted into temperature. Since the TMP36 has a 500 mV offset and changes by 10 mV per °C, the code subtracts 0.5 volts and multiplies by 100 to get degrees Celsius.

After calculating the temperature, the code compares it to a threshold. If the temperature is above the threshold, the red LED turns on, the fan turns on, and the LCD says the system is hot. If the temperature is below the threshold, the green LED turns on, the fan turns off, and the LCD says the system is cool.

Source Code

This is the full Arduino source code for my temperature controlled cooling system.

#include <LiquidCrystal.h>

// LCD pins: RS, E, D4, D5, D6, D7
LiquidCrystal lcd(12, 11, 5, 4, 3, 2);

// Pin setup
const int tempPin = A0;
const int redLedPin = 8;
const int greenLedPin = 7;
const int fanPin = 9;

// Temperature limit in Celsius
const float hotTemp = 30.0;

void setup() {
  pinMode(redLedPin, OUTPUT);
  pinMode(greenLedPin, OUTPUT);
  pinMode(fanPin, OUTPUT);

  lcd.begin(16, 2);
  lcd.clear();

  lcd.setCursor(0, 0);
  lcd.print("Auto Cooler");
  lcd.setCursor(0, 1);
  lcd.print("Starting...");
  delay(1500);
}

void loop() {
  int sensorValue = analogRead(tempPin);

  // Convert Arduino ADC reading to voltage.
  // Arduino Uno ADC is 10-bit, so values go from 0 to 1023.
  float voltage = sensorValue * (5.0 / 1023.0);

  // TMP36 formula:
  // Temperature C = (Voltage - 0.5) * 100
  float temperatureC = (voltage - 0.5) * 100.0;

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

  if (temperatureC >= hotTemp) {
    digitalWrite(redLedPin, HIGH);
    digitalWrite(greenLedPin, LOW);
    digitalWrite(fanPin, HIGH);

    lcd.setCursor(0, 1);
    lcd.print("HOT Fan ON");
  } else {
    digitalWrite(redLedPin, LOW);
    digitalWrite(greenLedPin, HIGH);
    digitalWrite(fanPin, LOW);

    lcd.setCursor(0, 1);
    lcd.print("COOL Fan OFF");
  }

  delay(500);
}

Debugging and Testing

This project took some trial and error. I had to check the wiring several times because one wrong connection on the breadboard can make the sensor, LCD, LED, or motor act wrong. I also had to make sure the TMP36 was facing the correct direction because it looks similar to a transistor but works differently.

I tested the system by touching or holding the TMP36 sensor to warm it up. When the sensor temperature increased, the LCD showed the temperature, the red LED turned on, and the fan motor turned on. When the sensor cooled back down, the green LED turned on and the fan shut off.

What I Learned

This week helped me understand how embedded programming connects inputs and outputs. The TMP36 sensor was the input, and the LEDs, LCD, and motor were the outputs. The Arduino code connected e