Day 5

// Temperature-controlled fan with LCD
#include <DHT.h>
#include <LiquidCrystal_I2C.h>

#define DHT_PIN  4
#define DHT_TYPE DHT22
#define ENA_PIN  9
#define IN1_PIN  7
#define IN2_PIN  8
#define BUZZER   11
#define POT_PIN  A0

DHT dht(DHT_PIN, DHT_TYPE);
LiquidCrystal_I2C lcd(0x27, 16, 2);

const float MIN_TEMP = 20.0;  // fan starts
const float MAX_TEMP = 35.0;  // fan at 100%
float alarmThreshold;

void setup() {
  Serial.begin(9600);
  dht.begin();
  lcd.init(); lcd.backlight();
  pinMode(ENA_PIN, OUTPUT);
  pinMode(IN1_PIN, OUTPUT); pinMode(IN2_PIN, OUTPUT);
  pinMode(BUZZER, OUTPUT);
  digitalWrite(IN1_PIN, HIGH); digitalWrite(IN2_PIN, LOW); // always forward
  lcd.print("Temp Fan Control");
  delay(1500); lcd.clear();
}

void loop() {
  // Read threshold from pot
  alarmThreshold = map(analogRead(POT_PIN), 0, 1023, 25, 45);

  // Read sensor
  float temp = dht.readTemperature();
  float hum  = dht.readHumidity();
  if (isnan(temp) || isnan(hum)) { delay(2000); return; }

  // Calculate fan speed
  int speed = constrain(map(temp*10, MIN_TEMP*10, MAX_TEMP*10, 0, 255), 0, 255);
  analogWrite(ENA_PIN, speed);

  // Alarm
  bool alarm = temp > alarmThreshold;
  digitalWrite(BUZZER, alarm ? HIGH : LOW);

  // Display
  lcd.setCursor(0, 0);
  lcd.print("T:"); lcd.print(temp,1); lcd.print("C H:"); lcd.print(hum,0); lcd.print("%  ");
  lcd.setCursor(0, 1);
  lcd.print("Fan:"); lcd.print(map(speed,0,255,0,100)); lcd.print("% A:");
  lcd.print(alarmThreshold,0); lcd.print("C  ");

  // Serial log CSV
  Serial.print(millis()); Serial.print(",");
  Serial.print(temp,1); Serial.print(",");
  Serial.print(hum,1);  Serial.print(",");
  Serial.print(speed);  Serial.print(",");
  Serial.println(alarm ? "ALARM" : "OK");

  delay(2000);
}