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Introduction 
Published date: 19/11/2016
In this "how to" guide i will show you how to make your own digital clock-thermometer with the Arduino Pro mini board. (yes, you can use any other Arduino boad) .

You will be able to change the current date and time with Set-Up-Down buttons. The "down" button can also be used to turn on/off the screen backlight.  The time and date values are stored in memory of the RTC.

The Temperature and humidity values updated every 5 seconds. We will use the DHT-21 sensor, but you can also use the DHT-11 and DHT-22 versions (you will need to make some changes in the code below). 

​Watch the presentation video below.

What you will need - Hardware

For this project you will need:
If you want you can use a rechargeable battery and a charging circuit as I did. (I used an old 950mAh mobile phone battery)
Or you can simply use one DC jack and one 5V power adapter to power it up.

The circuit

The circuit is realy simple.

The i2c lcd and RTC module must be connected to the Arduino SDA and SCL pins. If you are using the Arduino uno or Arduino Pro Mini (or another board based in atMega328p micro controller), use the I2C interface at A4 (SDA) and A5(SCL) pins.
​
I2C LCD 16x2:
  • Vcc to power source (max 5V!)
  • GND to GND
  • SDA to pin A4
  • SCL to pin A5
RTC DS1307 module:
  • Vcc to power source (max 5V!)
  • GND to GND
  • SDA to pin A4
  • SCL to pin A5
DHT-21:
  • Red cable to power source (max 5V!)
  • Black cable to GND
  • Yellow cable to pin 5
Push buttons:
  • Set button to pin 8
  • Up button to pin 9
  • Down button to pin 10
  • The second pin of all buttons must be connected to ground (GND) 

The code

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/*  Clock - Thermometer with Arduino
 *  More info: http://www.ardumotive.com/
 *  Dev: Michalis Vasilakis Data: 19/11/2016 Ver: 1.0
 *  
 *  Display 16x2:         Setup:
 *  +----------------+  +----------------+
 *  |HH:MM DD/MM/YYYY|  |    >HH :>MM    |
 *  |Temp:27c Hum:74%|  |>DD />MM />YYYY |
 *  +----------------+  +----------------+
 */

//Libraries
#include <Wire.h>
#include <RTClib.h>
#include <LiquidCrystal_I2C.h>
#include <dht.h>

//Init libraries objects
RTC_DS1307 rtc;
LiquidCrystal_I2C lcd(0x3F, 2, 1, 0, 4, 5, 6, 7, 3, POSITIVE);  // Set the LCD I2C address, if it's not working try 0x27.
dht DHT;

//Constants
char daysOfTheWeek[7][12] = {"Sunday","Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"};
#define DHT21_PIN 5     // DHT 22  (AM2302) - what pin we're connected to
const long interval = 6000;  // Read data from DHT every 6 sec
const int btSet = 8;
const int btUp = 9;
const int btDown = 10;

//Variables
int DD,MM,YY,H,M,S,temp,hum, set_state, up_state, down_state;
int btnCount = 0;
unsigned long previousMillis = 0;
unsigned long currentMillis; 
String sDD;
String sMM;
String sYY;
String sH;
String sM;
String sS;
boolean backlightON = true;
boolean setupScreen = false;


void setup () {
  pinMode(btSet, INPUT_PULLUP);
  pinMode(btUp, INPUT_PULLUP);
  pinMode(btDown, INPUT_PULLUP);
  lcd.begin(16,2);   // iInit the LCD for 16 chars 2 lines
  lcd.backlight();   // Turn on the backligt (try lcd.noBacklight() to turn it off)
  lcd.clear();
}

void loop () {
  currentMillis = millis();
  readBtns();
  getTempHum();    
  getTimeDate();
  if (!setupScreen){
    lcdPrint();
  }
  else{
    lcdSetup();
  }
}
//Read buttons
void readBtns(){
  set_state = digitalRead(btSet);
  up_state = digitalRead(btUp);
  down_state = digitalRead(btDown);
  //Turn backlight on/off by pressing the down button
  if (down_state==LOW && btnCount==0){
    if (backlightON){
      lcd.noBacklight();
      backlightON = false;
    }
    else{
      lcd.backlight();
      backlightON = true;
    }
    delay(500);
  }
  if (set_state==LOW){
    if(btnCount<5){
      btnCount++;
      setupScreen = true;
        if(btnCount==1){
          lcd.clear();
          lcd.setCursor(0,0);
          lcd.print("------SET------");
          lcd.setCursor(0,1);
          lcd.print("-TIME and DATE-");
          delay(2000);
          lcd.clear();
        }
    }
    else{
      lcd.clear();
      rtc.adjust(DateTime(YY, MM, DD, H, M, 0));
      lcd.print("Saving....");
      delay(2000);
      lcd.clear();
      setupScreen = false;
      btnCount=0;
    }
    delay(500);
  }
}
//Read temperature and humidity every 6 seconds from DHT sensor
void getTempHum(){
  if (currentMillis - previousMillis >= interval) {
    int chk = DHT.read21(DHT21_PIN);
    previousMillis = currentMillis;    
    hum = DHT.humidity;
    temp= DHT.temperature;
  }
}
//Read time and date from rtc ic
void getTimeDate(){
  if (!setupScreen){
    DateTime now = rtc.now();
    DD = now.day();
    MM = now.month();
    YY = now.year();
    H = now.hour();
    M = now.minute();
    S = now.second();
  }
  //Make some fixes...
  if (DD<10){ sDD = '0' + String(DD); } else { sDD = DD; }
  if (MM<10){ sMM = '0' + String(MM); } else { sMM = MM; }
  sYY=YY;
  if (H<10){ sH = '0' + String(H); } else { sH = H; }
  if (M<10){ sM = '0' + String(M); } else { sM = M; }
  if (S<10){ sS = '0' + String(S); } else { sS = S; }
}
//Print values to the display
void lcdPrint(){
  lcd.setCursor(0,0); //First row
  lcd.print(sH);
  lcd.print(":");
  lcd.print(sM);
  lcd.print(" ");
  lcd.print(sDD);
  lcd.print("/");
  lcd.print(sMM);
  lcd.print("/");
  lcd.print(sYY);
  lcd.setCursor(0,1); //Second row
  lcd.print("Temp:");
  lcd.print(temp);
  lcd.print("c");
  lcd.setCursor(9,1); //10 cell of second row
  lcd.print("Hum:");
  lcd.print(hum);
  lcd.print("%");
}
//Setup screen
void lcdSetup(){
  if (btnCount==1){
    lcd.setCursor(4,0);
    lcd.print(">"); 
    if (up_state == LOW){
      if (H<23){
        H++;
      }
      else {
        H=0;
      }
      delay(500);
    }
    if (down_state == LOW){
      if (H>0){
        H--;
      }
      else {
        H=23;
      }
      delay(500);
    }
  }
  else if (btnCount==2){
    lcd.setCursor(4,0);
    lcd.print(" ");
    lcd.setCursor(9,0);
    lcd.print(">");
    if (up_state == LOW){
      if (M<59){
        M++;
      }
      else {
        M=0;
      }
      delay(500);
    }
    if (down_state == LOW){
      if (M>0){
        M--;
      }
      else {
        M=59;
      }
      delay(500);
    }
  }
  else if (btnCount==3){
    lcd.setCursor(9,0);
    lcd.print(" ");
    lcd.setCursor(0,1);
    lcd.print(">");
    if (up_state == LOW){
      if (DD<31){
        DD++;
      }
      else {
        DD=1;
      }
      delay(500);
    }
    if (down_state == LOW){
      if (DD>1){
        DD--;
      }
      else {
        DD=31;
      }
      delay(500);
    }
  }
  else if (btnCount==4){
    lcd.setCursor(0,1);
    lcd.print(" ");
    lcd.setCursor(5,1);
    lcd.print(">");
    if (up_state == LOW){
      if (MM<12){
        MM++;
      }
      else {
        MM=1;
      }
      delay(500);
    }
    if (down_state == LOW){
      if (MM>1){
        MM--;
      }
      else {
        MM=12;
      }
      delay(500);
    }
  }
  else if (btnCount==5){
    lcd.setCursor(5,1);
    lcd.print(" ");
    lcd.setCursor(10,1);
    lcd.print(">");
    if (up_state == LOW){
      if (YY<2999){
        YY++;
      }
      else {
        YY=2000;
      }
      delay(500);
    }
    if (down_state == LOW){
      if (YY>2000){
        YY--;
      }
      else {
        YY=2999;
      }
      delay(500);
    }
  }
  lcd.setCursor(5,0);
  lcd.print(sH);
  lcd.setCursor(8,0);
  lcd.print(":");
  lcd.setCursor(10,0);
  lcd.print(sM);
  lcd.setCursor(1,1);
  lcd.print(sDD);
  lcd.setCursor(4,1);
  lcd.print("/");
  lcd.setCursor(6,1);
  lcd.print(sMM);
  lcd.setCursor(9,1);
  lcd.print("/");
  lcd.setCursor(11,1);
  lcd.print(sYY);
}
Download the code from here and open it with Arduino IDE. Inside you will also find all necessary​ libraries. 
clock_and_thermometer_i2clcd_dht21.zip
File Size: 6350 kb
File Type: zip
Download File
If have any difficulties with the i2c LCD complete this tutorial.

3D printing files

Here you will find the ipl and stl files of our box. You are free to make any changes you want. We made the 3d sketches with Autodesk Inventor 2017.
3dprintedbox.zip
File Size: 367 kb
File Type: zip
Download File

Well done!

Great news! You have successfully complete this guide and now you have your own Arduino digital clock/thermometer!
​
I hope you liked this, let me know in the comments!

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