#include <Arduino.h>

uint8_t PINS[6] = {7,6,5,4,3,2};

// array of the LED connections, cathode[0] andode[1]
uint8_t LEDS[24][2] =
{
  {6,1},                        // seconds LED
  {2,1}, {1,2}, {3,1}, {1,3},   // 5-hour
  {4,1}, {1,4}, {5,1}, {1,5},   // 1-hour
  {4,3}, {3,4}, {3,2}, {2,3}, {4,2}, {2,4}, {5,2}, {2,5}, {6,2}, {2,6}, {1,6}, // 5-minute
  {5,3}, {3,5}, {6,3}, {3,6}    // 1-minute
};

uint8_t framebuffer[24];

void setup() 
{
  for (uint8_t i = 0; i < 24; i++)
  {
    framebuffer[i] = 0;
  }
}

void loop() 
{
  static uint8_t i=0;

  uint8_t anode, cathode;

  cathode = PINS[ LEDS[i][0] -1 ];
  anode   = PINS[ LEDS[i][1] -1 ];

  // switch off voltages
  digitalWrite(cathode, LOW);
  digitalWrite(anode,   LOW);

  // switch to input
  pinMode(cathode, INPUT);
  pinMode(anode,   INPUT);
  
  // next LED
  i++;
  i %= 24;   //modulo 24
  cathode = PINS[ LEDS[i][0] -1 ];
  anode   = PINS[ LEDS[i][1] -1 ];

  // switch to outputs
  pinMode(cathode, OUTPUT);
  pinMode(anode,   OUTPUT);

  // switch voltages
  digitalWrite(cathode, LOW);
  digitalWrite(anode,   HIGH);

  delay(0.4);

}