Repurposing an Old Voltmeter

// Using a DHT 22 on pin 7 and a 0.96 inch OLED display

#include <DHT.h>
#include <U8g2lib.h>
#include "RTClib.h"

U8G2_SH1106_128X64_NONAME_F_HW_I2C u8g2(U8G2_R0, U8X8_PIN_NONE);

RTC_DS1307 RTC;

//Constants
#define DHTPIN 7              // PIN for DHT 22
#define DHTTYPE DHT22         //DHT 22 (AM2302)
DHT dht(DHTPIN, DHTTYPE);

//Variabler
int count;
int chk;                      //counter for cursor
float hum;                    //Stores humidity value
float temp;                   //Stores temperature value

void setup(void)
{
  u8g2.begin();
  RTC.begin();

  if (! RTC.isrunning()) {
    // following line sets the RTC to the date & time this sketch was compiled
    RTC.adjust(DateTime(__DATE__, __TIME__));
  }
}

void TempHum() {                                            // write temp and hum on OLED
  u8g2.clearBuffer();
  u8g2.setContrast(255);
  u8g2.drawRFrame(0 - chk, 0, 128, 64, 7);
  u8g2.setFont( u8g2_font_helvB24_tf);                      // Font
  u8g2.setCursor( 17 - chk, 28);                            // Kursor
  u8g2.print(temp, 1);                                      // Write temp
  u8g2.drawCircle(80 - chk, 5, 2, U8G2_DRAW_ALL);           // Make a °
  u8g2.print(" C");                                        // Celsius
  u8g2.setCursor( 17 - chk, 60);                            // Cursor
  u8g2.print(hum, 1);                                        // write hum
  u8g2.print(" %");                                         // Write %
  u8g2.sendBuffer();
}

void dateTime() {                                         //Write date and time on OLED
  DateTime now = RTC.now();
  u8g2.clearBuffer();
  u8g2.drawRFrame(0 - chk, 0, 128, 64, 7);
  u8g2.setFont( u8g2_font_timB24_tn);                     // Font
  u8g2.setCursor(5 - chk, 27);                            // Kursor
  if (now.hour() < 10)
    u8g2.print("0");
  u8g2.print(now.hour(), DEC);                            // Write hour
  u8g2.print(":");
  if (now.minute() < 10)
    u8g2.print("0");
  u8g2.print(now.minute(), DEC);                           // Write hour
  u8g2.print(":");
  if (now.second() < 10)
    u8g2.print("0");
  u8g2.print(now.second(), DEC);
  u8g2.setCursor( 7 - chk, 60);                            // Cursor
  u8g2.setFont( u8g2_font_timB18_tn);                      // Font
  u8g2.print(now.year(), DEC);                             // Write year
  u8g2.print("-");
  if (now.month() < 10)
    u8g2.print("0");
  u8g2.print(now.month(), DEC);                            // Write month
  u8g2.print("-");
  if (now.day() < 10)
    u8g2.print("0");
  u8g2.print(now.day(), DEC);                              // write day
  u8g2.sendBuffer();
}

void loop(void)
{
  chk = -128;
  do {                                    // let Temp and hum slide in
    TempHum();
    chk = chk + 1;
    delay(1);
  } while (chk < 1);

  delay(3000);

  hum = dht.readHumidity();               // read hum
  temp = dht.readTemperature();           // read temp

  chk = 0;
  do {                                    // let Temp and hum slide out
    TempHum();
    delay(1);
    chk = chk + 1;
  } while (chk < 129);

  chk = -128;
  do {                                    // let time and date slide in
    dateTime();
    chk = chk + 1;
    delay(1);
  } while (chk < 0);

  count = 0;
  do {                          // split the delay of 3000 into six 500 delays to have a smoother sec display
    dateTime();
    delay(10);
    count = count + 1;
  } while (count < 30);

  chk = 0;
  do {                                   // let Temp and hum slide out
    dateTime();
    delay(1);
    chk = chk + 1;
  } while (chk < 129);
  chk = 0;
}