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

RTC_DS1307 rtc; 

U8G2_MAX7219_32X8_F_4W_SW_SPI u8g2(U8G2_R0, /* clock=*/ 11, /* data=*/ 12, /* cs=*/ 10, /* dc=*/ U8X8_PIN_NONE, /* reset=*/ U8X8_PIN_NONE);

char time_string[10]; 

void setup(void) {

  pinMode(4, OUTPUT); 
  digitalWrite(4, HIGH); 
  
  u8g2.begin(); 
  u8g2.setContrast(200); 

  if (! rtc.begin()) { 
    abort();
  }
  
}

void loop(void) {

  DateTime now = rtc.now(); 

  sprintf(time_string, "%d:%02d", now.hour(), now.minute()); 

  u8g2.setFont(u8g2_font_t0_11b_tn);  

  u8g2.clearBuffer(); 
  u8g2.drawStr(2, 8, time_string);  
  u8g2.sendBuffer(); 
  delay(1000); 

}