Smart Fan

1/*
2  This code controls a DC motor fan based on temperature readings from a thermistor. 
3  It includes a manual override feature using a button. In automatic mode, the fan speed 
4  is controlled according to the temperature. In manual mode, the fan runs at full speed. 
5  LEDs are used to indicate the current mode (auto or manual).
6*/
7/*
8  Board: Arduino Uno R4
9  Components:
10  - DC motor (fan) via transistor / driver
11  - Thermistor (10k NTC)
12  - Potentiometer (manual speed control)
13  - AUTO / MANUAL button
14  - ON / OFF button
15  - LEDs for AUTO and MANUAL modes
16*/
17/*
18  Board: Arduino Uno R4
19  Components:
20  - DC motor (fan) via transistor / driver
21  - Thermistor (10k NTC)
22  - Potentiometer (manual speed control)
23  - AUTO / MANUAL button
24  - ON / OFF button
25  - LEDs for AUTO and MANUAL modes
26*/
27
28// -------- PIN DEFINITIONS --------
29#define MOTOR_PIN 9
30#define TEMP_SENSOR_PIN A0
31#define POT_PIN A1
32
33#define MODE_BUTTON_PIN 2     // AUTO / MANUAL toggle
34#define POWER_BUTTON_PIN 6    // ON / OFF toggle
35
36#define LED_AUTO 3
37#define LED_MANUAL 4
38
39// -------- CONSTANTS --------
40#define TEMP_THRESHOLD 20     // °C
41#define MIN_PWM 150           // Minimum PWM so fan actually spins
42
43// -------- STATE VARIABLES --------
44bool manualMode = false;      // false = AUTO, true = MANUAL
45bool systemOn = true;         // master ON / OFF
46
47void setup() {
48  pinMode(MOTOR_PIN, OUTPUT);
49  pinMode(TEMP_SENSOR_PIN, INPUT);
50  pinMode(POT_PIN, INPUT);
51
52  pinMode(MODE_BUTTON_PIN, INPUT_PULLUP);
53  pinMode(POWER_BUTTON_PIN, INPUT_PULLUP);
54
55  pinMode(LED_AUTO, OUTPUT);
56  pinMode(LED_MANUAL, OUTPUT);
57
58  Serial.begin(9600);
59}
60
61void loop() {
62
63  // -------- POWER BUTTON (ON / OFF) --------
64  static bool lastPowerButtonState = HIGH;
65  bool powerButtonState = digitalRead(POWER_BUTTON_PIN);
66
67  if (powerButtonState == LOW && lastPowerButtonState == HIGH) {
68    systemOn = !systemOn;
69    delay(200); // debounce
70  }
71  lastPowerButtonState = powerButtonState;
72
73  // -------- MODE BUTTON (AUTO / MANUAL) --------
74  static bool lastModeButtonState = HIGH;
75  bool modeButtonState = digitalRead(MODE_BUTTON_PIN);
76
77  if (modeButtonState == LOW && lastModeButtonState == HIGH) {
78    manualMode = !manualMode;
79    delay(200); // debounce
80  }
81  lastModeButtonState = modeButtonState;
82
83  // -------- LED STATUS --------
84  digitalWrite(LED_AUTO, systemOn && !manualMode);
85  digitalWrite(LED_MANUAL, systemOn && manualMode);
86
87  // -------- FAN CONTROL --------
88  int pwm = 0;
89
90  if (!systemOn) {
91    // System OFF → fan forced OFF
92    pwm = 0;
93  }
94  else if (manualMode) {
95    // MANUAL MODE → potentiometer controls speed
96    int potValue = analogRead(POT_PIN);     // 0–1023
97    pwm = map(potValue, 0, 1023, 0, 255);
98    pwm = constrain(pwm, 0, 255);
99
100    Serial.print("MANUAL | PWM: ");
101    Serial.println(pwm);
102  }
103  else {
104    // AUTO MODE → temperature controls speed
105    float voltage = analogRead(TEMP_SENSOR_PIN) * 5.0 / 1023.0;
106    float temperature = voltageToTemperature(voltage);
107
108    if (temperature > TEMP_THRESHOLD) {
109      pwm = map(temperature, TEMP_THRESHOLD, 40, MIN_PWM, 255);
110      pwm = constrain(pwm, MIN_PWM, 255);
111    } else {
112      pwm = 0;
113    }
114
115    Serial.print("AUTO | Temp: ");
116    Serial.print(temperature, 2);
117    Serial.print(" C | PWM: ");
118    Serial.println(pwm);
119  }
120
121  analogWrite(MOTOR_PIN, pwm);
122  delay(300);
123}
124
125// -------- THERMISTOR FUNCTION --------
126float voltageToTemperature(float voltage) {
127  const float R0 = 10000.0;   // 10k at 25°C
128  const float B = 3950.0;
129  const float T0 = 298.15;    // 25°C in Kelvin
130  const float Vcc = 5.0;
131
132  if (voltage <= 0.01) return -100; // safety
133
134  float Rt = R0 * (Vcc / voltage - 1.0);
135  float tempK = 1.0 / ((log(Rt / R0) / B) + (1.0 / T0));
136
137  return tempK - 273.15;
138}