How to use a parallel to serial shift register using a micro

[Shane]

Though the Arduino has 14 Digital Input/Output pins and 6 Analog Input pins, it is not difficult to design a project that exceeds those capabilities, either with too few outputs or too few inputs (or both). This tutorial introduces the parallel to serial shift register.

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Code: Select all

//PARALLEL TO SERIAL SHIFT REGISTER (SN74LS165 8-BIT)

//DEFINE VARIABLES

//DEFINE SERIAL IN/OUT PINS
 int clockPin = 7;
 int latchPin = 8;
 int dataPin = 9;

//DEFINE SWITCH DATA VARIABLES
 int switchValue = 0; //variable to hold value of switch states
 int switchState = 0; //variable to read state of each switch


 void setup(){
 //start serial and set baud rate for serial window
 Serial.begin(9600);

 //define pin modes
 pinMode(clockPin, OUTPUT);
 pinMode(latchPin, OUTPUT);
 pinMode(dataPin, INPUT);
 }

void loop(){
 //set latchPin low and then high for shift register to collect latest parallel data
 digitalWrite (latchPin, LOW);
 //wait for the shift register to read data
 delayMicroseconds (10);
 //set latchPin high to end parallel read and begin serial transmission
 digitalWrite (latchPin, HIGH);

 //with the latch pin low, collect serial data
 switchValue = 0; //clear switchValue variable
 for (int i = 0; i <8; i ++){
 digitalWrite (clockPin, LOW); //set clock Pin low to prepare to read data
 switchState = digitalRead (dataPin); //read dataPin value
 switchValue = (switchValue << 1); //bitshift one to the left to open LSB to write switchState
 switchValue = switchValue | (!switchState); //add switchState value to LSB of switchValue
 digitalWrite (clockPin, HIGH); //complete BIT data transmission; prepare for next
 }

 Serial.println(switchValue, BIN); //debugging in serial window of switches 1 through 8)
 Serial.println(switchValue);
 Serial.println(switchValue, HEX);
 Serial.println();
 delay (2000); //wait to avoid overloading serial window 
 }

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Courtecy of UMASS AMHERST