arduino-lcd-dht11.ino

#include <TimerOne.h>
#include <DHT_U.h>
#include <DHT.h>
#include <LiquidCrystal.h>

LiquidCrystal lcd(7, 8, 9, 10, 11, 12);
DHT dht(2, DHT11);
bool fahrenheit = true;
long duration = 2L * 1000L; // millis
float t = 0.0;
float h = 0.0;

void initLCD() {
    lcd.clear();
    lcd.setCursor(0, 0);
    if (fahrenheit)
        lcd.print("Temp        0 *F");
    else
        lcd.print("Temp        0 *C");
    lcd.setCursor(0, 1);
    lcd.print("Humidity    0 %");
}

void updateTemp() {
    float newT = dht.readTemperature(false);
    if(!isnan(newT))
        t = newT;
    float newH = dht.readHumidity();
    if(!isnan(newH))
        h = newH;
}

void toggleUnits() {
    fahrenheit = !fahrenheit;
    initLCD();
    refreshDisplay();
}

void refreshDisplay() {
    printData(fahrenheit ? dht.convertCtoF(t) : t, 0, 11);
    printData(h, 1, 11);
}

void setup() {
    lcd.begin(16, 2);
    initLCD();
    dht.begin();
    attachInterrupt(digitalPinToInterrupt(3), toggleUnits, RISING);
    Timer1.initialize(duration * 1000L); // micros
    Timer1.attachInterrupt(refreshDisplay);
}

void printData(float d, int r, int o) {
    if(d > 100.0)
        o--;
    lcd.setCursor(o, r);
    lcd.print((int)d);
}

void loop() {
    delay(duration);
    updateTemp();
}