Back to ShiftOut Tutorial 

//**************************************************************//
//  Name    : shiftOutCode, Dual One By One                           //
//  Author  : Carlyn Maw, Tom Igoe                               //
//  Date    : 25 Oct, 2006                                       //
//  Version : 1.0                                                //
//  Notes   : Code for using a 74HC595 Shift Register            //
//          : to count from 0 to 255                             //
//**************************************************************//

//Pin connected to ST_CP of 74HC595
int latchPin = 8;
//Pin connected to SH_CP of 74HC595
int clockPin = 12;
////Pin connected to DS of 74HC595
int dataPin = 11;

//holder for infromation you're going to pass to shifting function
byte data = 0; 



void setup() {
  //set pins to output because they are addressed in the main loop
  pinMode(latchPin, OUTPUT);

}

void loop() {

  //function that blinks all the LEDs
  //gets passed the number of blinks and the pause time
  blinkAll_2Bytes(1,500); 

  // light each pin one by one using a function A
  for (int j = 0; j < 8; j++) {
    //ground latchPin and hold low for as long as you are transmitting
    digitalWrite(latchPin, 0);
    //red LEDs
    lightShiftPinA(7-j);
    //green LEDs
    lightShiftPinA(j);
    //return the latch pin high to signal chip that it 
    //no longer needs to listen for information
    digitalWrite(latchPin, 1);
    delay(1000);
  }

  // light each pin one by one using a function A
  for (int j = 0; j < 8; j++) {
    //ground latchPin and hold low for as long as you are transmitting
    digitalWrite(latchPin, 0);
    //red LEDs
    lightShiftPinB(j);
    //green LEDs
    lightShiftPinB(7-j);
    //return the latch pin high to signal chip that it 
    //no longer needs to listen for information
    digitalWrite(latchPin, 1);
    delay(1000);
  } 

}

//This function uses bitwise math to move the pins up
void lightShiftPinA(int p) {
  //defines a local variable
  int pin;

  //this is line uses a bitwise operator
  //shifting a bit left using << is the same
  //as multiplying the decimal number by two. 
  pin = 1<< p;

  //move 'em out
  shiftOut(dataPin, clockPin, pin);   

}

//This function uses that fact that each bit in a byte
//is 2 times greater than the one before it to
//shift the bits higher
void lightShiftPinB(int p) {
  //defines a local variable
  int pin;

  //start with the pin = 1 so that if 0 is passed to this
  //function pin 0 will light. 
  pin = 1;

  for (int x = 0; x < p; x++) {
    pin = pin * 2; 
  }
  //move 'em out
  shiftOut(dataPin, clockPin, pin);   
}


// the heart of the program
void shiftOut(int myDataPin, int myClockPin, byte myDataOut) {
  // This shifts 8 bits out MSB first, 
  //on the rising edge of the clock,
  //clock idles low

  //internal function setup
  int i=0;
  int pinState;
  pinMode(myClockPin, OUTPUT);
  pinMode(myDataPin, OUTPUT);

  //clear everything out just in case to
  //prepare shift register for bit shifting
  digitalWrite(myDataPin, 0);
  digitalWrite(myClockPin, 0);

  //for each bit in the byte myDataOut�
  //NOTICE THAT WE ARE COUNTING DOWN in our for loop
  //This means that %00000001 or "1" will go through such
  //that it will be pin Q0 that lights. 
  for (i=7; i>=0; i--)  {
    digitalWrite(myClockPin, 0);

    //if the value passed to myDataOut and a bitmask result 
    // true then... so if we are at i=6 and our value is
    // %11010100 it would the code compares it to %01000000 
    // and proceeds to set pinState to 1.
    if ( myDataOut & (1<<i) ) {
      pinState= 1;
    }
    else {	
      pinState= 0;
    }

    //Sets the pin to HIGH or LOW depending on pinState
    digitalWrite(myDataPin, pinState);
    //register shifts bits on upstroke of clock pin  
    digitalWrite(myClockPin, 1);
    //zero the data pin after shift to prevent bleed through
    digitalWrite(myDataPin, 0);
  }

  //stop shifting
  digitalWrite(myClockPin, 0);
}


//blinks both registers based on the number of times you want to 
//blink "n" and the pause between them "d"
//starts with a moment of darkness to make sure the first blink
//has its full visual effect.
void blinkAll_2Bytes(int n, int d) {
  digitalWrite(latchPin, 0);
  shiftOut(dataPin, clockPin, 0);
  shiftOut(dataPin, clockPin, 0);
  digitalWrite(latchPin, 1);
  delay(200);
  for (int x = 0; x < n; x++) {
    digitalWrite(latchPin, 0);
    shiftOut(dataPin, clockPin, 255);
    shiftOut(dataPin, clockPin, 255);
    digitalWrite(latchPin, 1);
    delay(d);
    digitalWrite(latchPin, 0);
    shiftOut(dataPin, clockPin, 0);
    shiftOut(dataPin, clockPin, 0);
    digitalWrite(latchPin, 1);
    delay(d);
  }
}