Multiplexing with Arduino and the 74HC59

Multiplexing with Arduino and the 74HC595

The 74HC595 is an easy and inexpensive (at about 60 cents apiece) way to increase the number of digital out pins on your Arduino.  In this tutorial I'll show you how to drive up to 16 LEDs with one 74HC595 using a technique called multiplexing.  In the end, all 16 LEDs will require only three of the Arduino's available digital pins.

What Is Multiplexing?

SHEMA & COMPENENT

20Ohm resistors should be brown, red, brown, gold

EXEMPLE CODE

/*
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
*/

//this code will light up each led in the 4x4 matrix one at a time


//pin connections- the #define tag will replace all instances of "latchPin" in your code with A1 (and so on)
#define latchPin A1
#define clockPin A0
#define dataPin A2

//looping variables
byte i;
byte j;

//storage variable
byte dataToSend;

void setup() {
  //set pins as output
  pinMode(latchPin, OUTPUT);
  pinMode(clockPin, OUTPUT);
  pinMode(dataPin, OUTPUT);
}

void loop() {

  for (i=0;i<4;i++){
 
    for (j=0;j<4;j++){
   
      //bit manipulation (more info at http://arduino.cc/en/Reference/Bitshift ,  http://arduino.cc/en/Reference/BitwiseXorNot , and http://arduino.cc/en/Reference/BitwiseAnd)
      dataToSend = (1 << (i+4)) | (15 & ~(1 << j));//preprare byte (series of 8 bits) to send to 74HC595
      //for example when i =2, j = 3,
      //dataToSend = (1 << 6) | (15 & ~(1 << 3));
      //dataToSend = 01000000 | (15 & ~(00001000));
      //dataToSend = 01000000 | (15 & 11110111);
      //dataToSend = 01000000 | (15 & 11110111);
      //dataToSend = 01000000 | 00000111;
      //dataToSend = 01000111;
      //the first four bits of dataToSend go to the four rows (anodes) of the LED matrix- only one is set high and the rest are set to ground
      //the last four bits of dataToSend go to the four columns (cathodes) of the LED matrix- only one is set to ground and the rest are high
      //this means that going through i = 0 to 3 and j = 0 to three with light up each led once
   
      // setlatch pin low so the LEDs don't change while sending in bits
      digitalWrite(latchPin, LOW);
      // shift out the bits of dataToSend to the 74HC595
      shiftOut(dataPin, clockPin, LSBFIRST, dataToSend);
      //set latch pin high- this sends data to outputs so the LEDs will light up
      digitalWrite(latchPin, HIGH);
   
      delay(500);//wait
    }
  }

}