humitemp1.ino

// Humidity and temperature monitor
// for Arduino UNO R3 (and probably most others)
// Main pieces:
//  DHT11 humidity/temp sensor
//    - mandatory 10k pull-up resistor
//    -> using DHT.f by adafruit at https://github.com/adafruit/DHT-sensor-library
//  16x2 LCD
//    - 10K potentiometer for contrast control
//    - Push button and transistor for backlight control
//    - 220ohm resistor to make the backlight a bit darker
//    -> using LiquidCrystal builtin plugin for LCD

// code is hacky, horribly built, unprofessinally organized, and works!

#include <LiquidCrystal.h>

#include "DHT.h"

// pins
#define DHTPIN 14
#define LEDPIN 13
#define BTNPIN 8
#define TRANSPIN 9

// init DHT
#define DHTTYPE DHT11   // DHT 11 
#define FAHRENHEIT true
DHT dht(DHTPIN, DHTTYPE);

// init LCD
LiquidCrystal lcd(6, 7, 2, 3, 4, 5);

// button state
long last_button_press = 0;
boolean is_active = false;

// graphics ;)
byte marker1[8] = {
  0b10000,
  0b01000,
  0b01000,
  0b00100,
  0b00100,
  0b00010,
  0b00010,
  0b00000
};
byte marker2[8] = {
  0b00100,
  0b00100,
  0b00100,
  0b00100,
  0b00100,
  0b00100,
  0b00100,
  0b00000
};
byte marker3[8] = {
  0b00001,
  0b00010,
  0b00010,
  0b00100,
  0b00100,
  0b01000,
  0b01000,
  0b00000
};
byte marker4[8] = {
  0b00000,
  0b00000,
  0b00000,
  0b11111,
  0b00000,
  0b00000,
  0b00000,
  0b00000
};
byte next_marker = 0;

void setup() {
  //pushbutton with internal pull-up resistor
  pinMode(BTNPIN, INPUT);
  digitalWrite(BTNPIN, HIGH);

  // transistor
  pinMode(TRANSPIN, OUTPUT);
  
  // forget about the internal led
  pinMode(LEDPIN, OUTPUT);
  digitalWrite(LEDPIN, LOW);
 
  dht.begin();

  lcd.createChar(0, marker1);
  lcd.createChar(1, marker2);
  lcd.createChar(2, marker3);
  lcd.createChar(3, marker4);  
  lcd.begin(16, 2);

  // the LCD template. Values will be written later
  lcd.print("Humidity:   %");
  lcd.setCursor(0, 1);
  lcd.print("Temp    :     F");
  
  // let everything settle
  delay(1000);
  
  // and go to sleep
  displayOff();
}

// booleanize it. 
// also - true if digitalRead is false (!)
// because it is counter intuitive, we keep it
// in a dedicated function.
boolean isButtonPressed() {
  int button_pressed = !digitalRead(BTNPIN); // pin low -> pressed
  return button_pressed;
}

void displayOn() {
  digitalWrite(TRANSPIN, HIGH);
  lcd.display();
}

void displayOff() {
  digitalWrite(TRANSPIN, LOW);
  lcd.noDisplay();
}

void loop() {
  boolean button_pressed = isButtonPressed();
  if (!button_pressed) {
    if (is_active) {
      if ((millis() - last_button_press > 10000)) {
        is_active = false;
        displayOff();
      }
    }
  } else {
    last_button_press = millis();
    is_active = true;
    displayOn();
  }
  if (is_active) {
    digitalWrite(LEDPIN, HIGH);
    // this is not optimal. one should be able to read both
    // value with a single actuall read from the sensor.
    // I think that the DHT11 library is reading twice.
    float h = dht.readHumidity();
    float t = dht.readTemperature(FAHRENHEIT);
  
    // check if returns are valid, if they are NaN (not a number) then something went wrong!
    if (!isnan(t) && !isnan(h)) {
      lcd.setCursor(10, 0);
      lcd.print(h,0);
      lcd.setCursor(10, 1);
      lcd.print(t, 1);
      lcd.setCursor(15, 0);
      lcd.write(next_marker);
      next_marker = ((next_marker+1) % 4);
    }
    digitalWrite(LEDPIN, LOW);
    delay(2000);
  } else {
    delay(50);
  }
}