Getting started with Arduino and SPI.h

basics-arduino-spi

#include <SPI.h>

// define pins and other variables
const int latchPin = 8;
const int clockPin = 13;
const int dataPin  = 11;

// setup the correct pins and initialize SPI library
void setup() {
  // setup pins
  pinMode(latchPin, OUTPUT);
  pinMode(clockPin, OUTPUT);
  pinMode(dataPin,  OUTPUT);
  
  // setup SPI library
  SPI.setBitOrder(MSBFIRST);
  SPI.setDataMode(SPI_MODE0);
  SPI.setClockDivider(SPI_CLOCK_DIV2);
  SPI.begin();
}

void loop() {
  for(int i =0; i < 16; i++){
    turnOnLed(i);
  }
}

// turn on correct LED using 595's
void turnOnLed(int ledNr) {
  digitalWrite(latchPin, LOW);

  if (ledNr >= 8) {
    SPI.transfer(1<<ledNr-8);
    SPI.transfer(0);
  }
  else {
    SPI.transfer(0);
    SPI.transfer(1<<ledNr);
  }

  digitalWrite(latchPin, HIGH);
}