tank_cooler/firmware/firmware.ino

#define FAN_PIN    9 // D9
#define L_LED_PIN 13 // D13

#define BMP280_I2C_ADDRESS 0x76  // BMP280 conneciton: D1 = SCL; D2 = SDA

// minimum value to start both fan's is 110
// without queeking noise is 255
#define FAN_ON_TEMP      26.0
#define FAN_OFF_MAX_TEMP 24.5

#define FAN_ON_STATE  HIGH
#define FAN_OFF_STATE  LOW

#define BMP280_CHECK_INTERVAL_MS 2000 // every 60000 = 60 seconds

float bmp280_temp = -99.9;
uint32_t bmp280_lastcheck_millis = BMP280_CHECK_INTERVAL_MS;

uint8_t fan_state = LOW;

void setup()
{
  // put your setup code here, to run once:

  // setup serial
  Serial.begin(115200);
  Serial.println();
  delay(1000);

  // setup BMP280
  Serial.println("Sensor BMP280 init status: " + String(sensor_bmp280_begin(BMP280_I2C_ADDRESS)));
  bmp280_temp = sensor_bmp280_temperature();

  // setup FAN Pin
  pinMode(FAN_PIN, OUTPUT);

  pinMode(L_LED_PIN, OUTPUT);
}

void loop()
{
  // put your main code here, to run repeatedly:

  if ((bmp280_lastcheck_millis + BMP280_CHECK_INTERVAL_MS) <= millis())
  {
    bmp280_temp = sensor_bmp280_temperature();
    Serial.println("Temperature: " + String(bmp280_temp) + "°C");
    digitalWrite(L_LED_PIN, HIGH);

    if (fan_state > 0 && bmp280_temp <= FAN_OFF_MAX_TEMP)
    {
      fan_state = FAN_OFF_STATE;  // off
    }

    if (bmp280_temp >= FAN_ON_TEMP)
    {
      fan_state = FAN_ON_STATE;
    }

    Serial.println("FAN state: " + String(fan_state));

    digitalWrite(FAN_PIN, fan_state);

    digitalWrite(L_LED_PIN, LOW);

    bmp280_lastcheck_millis = millis();
  }

}