#include <Wire.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>

#define OLED_RESET 4
Adafruit_SSD1306 display(OLED_RESET);
#if (SSD1306_LCDHEIGHT != 32)
#error("Height incorrect, please fix Adafruit_SSD1306.h!");
#endif
int b=0;
int t=0;
int mt=0;
const long interval = 1000;
unsigned long previousMillis = 0;
unsigned long currentMillis = millis();
void setup()   {                
  Serial.begin(9600);
  // by default, we'll generate the high voltage from the 3.3v line internally! (neat!)
  display.begin(SSD1306_SWITCHCAPVCC, 0x3C);  // initialize with the I2C addr 0x3C (for the 128x32)
  // init done
  // Show image buffer on the display hardware.
  // Since the buffer is intialized with an Adafruit splashscreen
  // internally, this will display the splashscreen.
  display.display();
  delay(2000);
  //clear the adafruiy splashscreen
  display.clearDisplay();
  display.setCursor(12,8);
  display.setTextSize(2);
  display.setTextColor(WHITE);
  display.print("00:00:00");
  display.display();  
}
void loop() 
{
  seconds();
}
void seconds(void) //draw the alphabet
{
  display.setCursor(0,0);
  display.setTextSize(1);
  display.setTextColor(WHITE);
  for (uint8_t i=0; i < 22; i++) //168
  {
    if (i == '\n') continue;
    display.write(i+65);
  }
  unsigned long currentMillis = millis();
  if (currentMillis - previousMillis >= interval) 
    {
    previousMillis = currentMillis;// save the last time you changed the number
    display.setCursor(96,8);
    display.setTextSize(2);
    display.setTextColor(BLACK);
    //display.write(b+(28,DEC));
    delay(5);
    display.write(b+(48));
    delay(5);
    display.display();
    b++;
    if (b==10)
      {
      tenseconds();
      b=0;
      }
    delay(5);
    display.setCursor(96,8);
    display.setTextColor(WHITE);
    delay(5);
    display.write(b+48);
    delay(5);
    display.display();
    }
  display.setCursor(0,24);
  display.setTextSize(1);
  for (uint8_t i=0; i < 22; i++) //168
    {
    if (i == '\n') continue;
      display.write(i+65);
    }
  display.display();
}
void tenseconds()
{
  display.setCursor(84,8);
  display.setTextSize(2);
  display.setTextColor(BLACK);
  display.write(t+(48));
  display.display();
  t++;
  if (t==6)
    {
    t=0;
    minutes();
    }
  display.setCursor(84,8);
  display.setTextColor(WHITE);
  display.write(t+48);
  display.display();
}
void minutes()
{
  display.setCursor(60,8);
  display.setTextSize(2);
  display.setTextColor(BLACK);
  display.write(mt+(48));
  display.display();
  mt++;
  if (mt==10)
    {
    mt=0;
    //tminutes();
    }
  display.setCursor(60,8);
  display.setTextColor(WHITE);
  display.write(mt+48);
  display.display();
}