torkell | Arduino thermometer

What with the glorious sunny weather, I wondered how hot my flat actually gets. It's certainly felt far too warm recently.

Now, the sensible way to find out is to go and buy a thermometer. But Robert Days are closed for the evening. So instead I dug out an Arduino kit I was given for my birthday (Elegoo's "The Most Complete Starter Kit for the Mega 2560") and set to work...

The answer: 27°C!

I'm using a DHT11 combined temperature and humidity sensor and a generic LCD display showing the results, running off of a 9V battery so I can wander around with it. The nice thing about Arduino development is there are libraries for everything, so there's surprisingly little code behind this:

// Based off sample lessons 12 (DHT11) and 22 (LCD)

// DHT11 
#include <dht_nonblocking.h>
#define DHT_SENSOR_TYPE DHT_TYPE_11

static const int DHT_SENSOR_PIN = 2;
DHT_nonblocking dht_sensor( DHT_SENSOR_PIN, DHT_SENSOR_TYPE );

/*
 * Poll for a measurement, keeping the state machine alive.  Returns
 * true if a measurement is available.
 */
static bool measure_environment( float *temperature, float *humidity )
{
  static unsigned long measurement_timestamp = millis( );

/* Measure once every four seconds. */
  if( millis( ) - measurement_timestamp > 3000ul )
  {
    if( dht_sensor.measure( temperature, humidity ) == true )
    {
      measurement_timestamp = millis( );
      return( true );
    }
  }

return( false );
}

// LCD
// include the library code:
#include <LiquidCrystal.h>

// initialize the library with the numbers of the interface pins
LiquidCrystal lcd(7, 8, 9, 10, 11, 12);

void setup() {
  // set up the LCD's number of columns and rows:
  lcd.begin(16, 2);
  // Print a message to the LCD.
           //01234567890123456
  lcd.print("Temp:     ");
  
  lcd.setCursor(0, 1);
           //01234567890
  lcd.print("Humidity: ");
}

void loop() {
  float temperature;
  float humidity;

/* Measure temperature and humidity.  If the functions returns
     true, then a measurement is available. */
  if( measure_environment( &temperature, &humidity ) == true )
  {
    Serial.print( "T = " );
    Serial.print( temperature, 1 );
    Serial.print( " deg. C, H = " );
    Serial.print( humidity, 1 );
    Serial.println( "%" );
    
    lcd.setCursor(10, 0);
    lcd.print("       ");
    lcd.setCursor(10, 0);
    lcd.print(temperature, 1);
    lcd.print("C");
    lcd.setCursor(10, 1);
    lcd.print("       ");
    lcd.setCursor(10, 1);
    lcd.print(humidity, 1);
    lcd.print("%");
  }
}