Temperature-Controlled Automatic Cooling System

Aim

To design a system that measures ambient temperature with a sensor and automatically switches a fan (or any cooling device) ON or OFF according to a set threshold.

Overview

An analog temperature sensor module (NTC thermistor based, e.g. LM35 or an NTC module) outputs a voltage proportional to the room temperature. The Arduino reads this value on an analog input, converts it to degrees Celsius, and compares it with a user-defined threshold. When the temperature rises above the threshold, the controller drives a relay/transistor that powers the cooling fan. When the temperature falls back below the threshold (with a small hysteresis band to avoid rapid switching), the fan is turned OFF.

Components Required

• Arduino Uno
• NTC temperature sensor module (or LM35)
• Relay module (or transistor driver, e.g. 2N2222 + diode)
• DC fan (5V/12V)
• Green LED + 220 ohm resistor (fan ON indicator)
• Breadboard and jumper wires

Circuit Connections

Interactive Circuit Diagram

Simulate the circuit: adjust the sensor inputs below and watch the outputs react according to the control logic.

Working

1. Sensor continuously outputs a voltage proportional to temperature.
2. Arduino samples the analog channel every second and smooths it by averaging a few readings.
3. The averaged value is converted to Celsius using the sensor's transfer function.
4. If temperature > THRESHOLD + HYST, the relay pin is driven HIGH and the fan runs.
5. If temperature < THRESHOLD - HYST, the relay pin is driven LOW and the fan stops.
6. The status LED mirrors the relay state so the fan state is visible even when the fan is not connected.

Control Logic

Arduino Code

1// Practical 1: Temperature-Controlled Automatic Cooling System
2const int SENSOR_PIN = A0;    // Analog output of the temperature sensor
3const int RELAY_PIN  = 8;     // Relay / driver input for the fan
4const int LED_PIN    = 9;     // Fan status LED
5
6const float T_HI = 30.0;      // Fan turns ON above this temperature
7const float T_LO = 28.0;      // Fan turns OFF below this temperature
8
9float readTemperature() {
10  // Average 10 samples for a stable reading
11  long sum = 0;
12  for (int i = 0; i < 10; i++) {
13    sum += analogRead(SENSOR_PIN);
14    delay(5);
15  }
16  float adc = sum / 10.0;               // 0..1023
17  float volts = adc * 5.0 / 1023.0;     // 0..5 V
18  return volts * 100.0;                 // LM35: 10 mV per degree C
19}
20
21void setup() {
22  pinMode(RELAY_PIN, OUTPUT);
23  pinMode(LED_PIN, OUTPUT);
24  Serial.begin(9600);
25}
26
27void loop() {
28  float tempC = readTemperature();
29  Serial.print("Temp: ");
30  Serial.print(tempC);
31  Serial.print(" C -> ");
32
33  if (tempC > T_HI) {                   // Hot: start cooling
34    digitalWrite(RELAY_PIN, HIGH);
35    digitalWrite(LED_PIN, HIGH);
36    Serial.println("FAN ON");
37  } else if (tempC < T_LO) {            // Cooled down: stop fan
38    digitalWrite(RELAY_PIN, LOW);
39    digitalWrite(LED_PIN, LOW);
40    Serial.println("FAN OFF");
41  }
42  delay(1000);
43}