Arduino - ShftIn11

//  Name    : shiftIn Example 1.1                              //
//  Author  : Carlyn Maw                                        //
//  Date    : 25 Jan, 2007                                      //
//  Version : 1.0                                               //
//  Notes   : Code for using a CD4021B Shift Register       //
//          :                                                   //

//define where your pins are
int latchPin = 8;
int dataPin = 9;
int clockPin = 7;

//Define variables to hold the data
//for shift register.
//starting with a non-zero numbers can help
byte switchVar1 = 72;  //01001000

void setup() {

  //start serial


  //define pin modes

  pinMode(latchPin, OUTPUT);

  pinMode(clockPin, OUTPUT);

  pinMode(dataPin, INPUT);


void loop() {

  //Pulse the latch pin:

  //set it to 1 to collect parallel data


  //set it to 1 to collect parallel data, wait


  //set it to 0 to transmit data serially


  //while the shift register is in serial mode

  //collect each shift register into a byte

  //the register attached to the chip comes in first

  switchVar1 = shiftIn(dataPin, clockPin);

  //Print out the results.

  //leading 0's at the top of the byte

  //(7, 6, 5, etc) will be dropped before

  //the first pin that has a high input


  Serial.println(switchVar1, BIN);

//white space
//delay so all these print satements can keep up.


//------------------------------------------------end main loop

////// ----------------------------------------shiftIn function
///// just needs the location of the data pin and the clock pin
///// it returns a byte with each bit in the byte corresponding
///// to a pin on the shift register. leftBit 7 = Pin 7 / Bit 0= Pin 0

byte shiftIn(int myDataPin, int myClockPin) {

  int i;

  int temp = 0;

  int pinState;

  byte myDataIn = 0;

  pinMode(myClockPin, OUTPUT);

  pinMode(myDataPin, INPUT);
//we will be holding the clock pin high 8 times (0,..,7) at the
//end of each time through the for loop

//at the begining of each loop when we set the clock low, it will
//be doing the necessary low to high drop to cause the shift
//register's DataPin to change state based on the value
//of the next bit in its serial information flow.
//The register transmits the information about the pins from pin 7 to pin 0
//so that is why our function counts down

  for (i=7; i>=0; i--)


    digitalWrite(myClockPin, 0);


    temp = digitalRead(myDataPin);

    if (temp) {

      pinState = 1;

      //set the bit to 0 no matter what

      myDataIn = myDataIn | (1 << i);


    else {

      //turn it off -- only necessary for debuging

     //print statement since myDataIn starts as 0

      pinState = 0;


    //Debuging print statements


    //Serial.print("     ");

    //Serial.println (dataIn, BIN);

    digitalWrite(myClockPin, 1);


  //debuging print statements whitespace


  //Serial.println(myDataIn, BIN);

  return myDataIn;