Clock

int SER_Pin = 9;   //pin 14 on the 75HC595
int RCLK_Pin = 10;  //pin 12 on the 75HC595
int SRCLK_Pin = 11; //pin 11 on the 75HC595

#define number_of_74hc595s 1  //How many of the shift registers - change this
#define numOfRegisterPins number_of_74hc595s * 8 //do not touch
boolean registers[numOfRegisterPins];

unsigned long nextStep = 0;
unsigned long timer = 0;
unsigned long a = 1;
unsigned long b = 0;

int hourPin[] = {0,1,2,3};
int minPin[] = {4,5};
int secPin[] = {6,7};

int hourLen = 4;
int minLen = 2;
int secLen = 2;

int s = 500;
int aS;
int bS;

void setup(){
  pinMode(SER_Pin, OUTPUT);
  pinMode(RCLK_Pin, OUTPUT);
  pinMode(SRCLK_Pin, OUTPUT);

  Serial.begin(9600);

  //reset all register pins
  clearRegisters();
  writeRegisters();
  
  
  aS = minLen;
  bS = minLen*secLen;
  
}               

void loop(){s
  
  if(millis() > nextStep)
  {
    
    for(int i=0; i < secLen; i++)
    {
      if(i < (a % (secLen + 1)))
       {
         registers[secPin[i]] = HIGH;
       } else {
         registers[secPin[i]] = LOW;
       }
    }
    writeRegisters();
    
    if((timer % aS) == aS-1)
    { 
      for(int i=0; i < minLen; i++)
      {
         if(i < (a % (minLen + 1)))
         {
           registers[minPin[i]] = HIGH;
         } else {
           registers[minPin[i]] = LOW;
         }
         writeRegisters();
      }
      writeRegisters();
      a++;
    }
    
    if((timer % bS) == bS-1)
    {
      for(int i=0; i < hourLen; i++)
      {
        if(i < (b % (hourLen + 1)))
         {
           registers[hourPin[i]] = HIGH;
         } else {
           registers[hourPin[i]] = LOW;
         }
      }
      b++;
    }
    
    timer++;
    nextStep = millis() + s;
    
    
    
  }
  
}

//set all register pins to LOW
void clearRegisters(){
  for(int i = numOfRegisterPins - 1; i >=  0; i--){
     registers[i] = LOW;
  }
} 

//Set and display registers
//Only call AFTER all values are set how you would like (slow otherwise)
void writeRegisters(){
  digitalWrite(RCLK_Pin, LOW);
  for(int i = numOfRegisterPins - 1; i >=  0; i--){
    digitalWrite(SRCLK_Pin, LOW);
    int val = registers[i];
    digitalWrite(SER_Pin, val);
    digitalWrite(SRCLK_Pin, HIGH);
  }
  digitalWrite(RCLK_Pin, HIGH);
}

//set an individual pin HIGH or LOW
void setRegisterPin(int index, int value){
  registers[index] = value;
}