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Author Topic: How To Detect 22 Switches for MIDI Foot Controller  (Read 895 times)
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Hi, I have made a foot controller to control Ableton Live. It has 20 switches and there aren't enough digital inputs on the arduino to wire them normally. How can I detect 20 switches from 14 inputs? A 4x5 matrix? If so how would this work?

Once a keypress is detected I want to send serial data via USB to the computer to be interpreted in C or Processing to emulate a MIDI event as well as an ASCII key press. How would I do this also?

Thanks,

Matthew Hubble
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http://www.arduino.cc/en/Tutorial/ShiftIn
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If you need to read more inputs than the arduino has pins for, the answer my friend is multiplexing.  This can be done in software or you can use a multiplexing IC such as here
http://www.arduino.cc/playground/Learning/4051
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thanks very much trialex that is a really good resource I haven't seen before and its solved my problem. I am going to use 3 of the CD4021BE IC's daisy chained together to get 24 switches using only 3 pins. 20 of these switches are used. 2 other switches  are used to change the MIDI channel of the messages to give my foot controller 4 different functions. This is the code I intend to use:[code]//**************************************************************//
//  Name    : MIDI Foot Controller                              //
//  Author  : Matthew Hubble                                    //
//  Date    : 11 May, 2008                                      //
//  Version : 0.1                                               //
//  Notes   : Code for using a CD4021B Shift Register and           //
//          : sending MIDI                                      //
//**************************************************************//

//define pins
#define MIDIPin 1
#define ledPin 2
#define clockPin 3
#define dataPin 4
#define latchPin 5
#define modePin1 6
#define modePin2 7

//define bits
#define BIT1 1
#define BIT2 2
#define BIT3 3
#define BIT4 4
#define BIT5 5
#define BIT6 6
#define BIT7 7
#define BIT8 8

//define MIDI stuff
#define MIDICHANNEL1 1
#define MIDICHANNEL2 2
#define MIDICHANNEL3 3
#define MIDICHANNEL4 4
#define VELOCITY 127
#define ROOTNOTE1 1
#define ROOTNOTE2 9
#define ROOTNOTE3 17

//declare 3 bytes to hold the binary from 3 CD4021BE IC's
byte switchVar1 = 0;
byte switchVar2 = 0;
byte switchVar3 = 0;

int modePin1State;
int modePin2State;
int if_flag = 0;

void setup()
{
  //set MIDI baud rate
  Serial.begin(31250);
  
  //define pin modes
  pinMode(ledPin,OUTPUT);
  pinMode(latchPin, OUTPUT);
  pinMode(clockPin, OUTPUT);
  pinMode(dataPin, INPUT);
  pinMode(modePin1,INPUT);
  pinMode(modePin2,INPUT);
  
  //turn on internal pullup
  digitalWrite(modePin1, HIGH);
  digitalWrite(modePin2, HIGH);
}

void loop()
{
  //Pulse the latch pin:
  //set it to 1 to collect parallel data
  digitalWrite(latchPin,1);
  //set it to 1 to collect parallel data, wait
  delayMicroseconds(20);
  //set it to 0 to transmit data serially  
  digitalWrite(latchPin,0);

  //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);
  switchVar2 = shiftIn(dataPin, clockPin);
  switchVar3 = shiftIn(dataPin, clockPin);
  
  //get the state of the mode switches
  modePin1State = digitalRead(modePin1);
  modePin2State = digitalRead(modePin2);
  
  //send appropriate MIDI messages based on input
  switchtoMIDI(switchVar1, ROOTNOTE1);
  switchtoMIDI(switchVar2, ROOTNOTE2);
  switchtoMIDI(switchVar3, ROOTNOTE3);
}

//shiftIn function gets 8 bit binary string
byte shiftIn(int myDataPin, int myClockPin) {
  int i;
  int temp = 0;
  int pinState;
  byte myDataIn = 0;

  pinMode(myClockPin, OUTPUT);
  pinMode(myDataPin, INPUT);

  for (i=7; i>=0; i--)
  {
    //Set clockPin to LOW to recieve serial bit
    digitalWrite(myClockPin, 0);
    //wait to recieve bit
    delayMicroseconds(2);
    //read  1 or 0
    temp = digitalRead(myDataPin);
    if (temp)
    {
      pinState = 1;
      myDataIn = myDataIn | (1 << i);
    }
    else
    {
      pinState = 0;
    }
    
    //set clockPin to HIGH ready for the next bit
    digitalWrite(myClockPin, 1);

  }
  return myDataIn;
}

// send a MIDI note-on message
void noteOn(byte channel, byte note, byte velocity)
{
  midiMsg( (0x90 | (channel << 4)), note, velocity);
}

// send a MIDI note-off message
void noteOff(byte channel, byte note, byte velocity)
{
  midiMsg( (0x80 | (channel<<4)), note, velocity);
}

// send a general MIDI message
void midiMsg(byte cmd, byte data1, byte data2)
{
  digitalWrite(ledPin,HIGH);  // indicate we're sending MIDI data
  Serial.print(cmd, BYTE);
  Serial.print(data1, BYTE);
  Serial.print(data2, BYTE);
  digitalWrite(ledPin,LOW);
}

//send MIDI messages based on the mode switches and the MIDI switches
void switchtoMIDI(byte switchVar, int rootnote)
{
  if(modePin1State == HIGH && modePin2State == HIGH && if_flag == 0)
  {
    if(switchVar & BIT1 == 1)
    {
      noteOn(MIDICHANNEL1,rootnote,VELOCITY);
      delayMicroseconds(1);
      noteOff(MIDICHANNEL1,rootnote,VELOCITY);
    }
    
    if(switchVar & BIT2 == 2)
    {
      noteOn(MIDICHANNEL1,(rootnote + 1),VELOCITY);
      delayMicroseconds(1);
      noteOff(MIDICHANNEL1,(rootnote + 1),VELOCITY);
    }
    
    if(switchVar & BIT3 == 3)
    {
      noteOn(MIDICHANNEL1,(rootnote + 2),VELOCITY);
      delayMicroseconds(1);
      noteOff(MIDICHANNEL1,(rootnote + 2),VELOCITY);
    }
    
    if(switchVar & BIT4 == 4)
    {
      noteOn(MIDICHANNEL1,(rootnote + 3),VELOCITY);
      delayMicroseconds(1);
      noteOff(MIDICHANNEL1,(rootnote + 3),VELOCITY);
    }
    
    if(switchVar & BIT5 == 5)
    {
      noteOn(MIDICHANNEL1,(rootnote + 4),VELOCITY);
      delayMicroseconds(1);
      noteOff(MIDICHANNEL1,(rootnote + 4),VELOCITY);
    }
    
    if(switchVar & BIT6 == 6)
    {
      noteOn(MIDICHANNEL1,(rootnote + 5),VELOCITY);
      delayMicroseconds(1);
      noteOff(MIDICHANNEL1,(rootnote + 5),VELOCITY);
    }
    
    if(switchVar & BIT7 == 7)
    {
      noteOn(MIDICHANNEL1,(rootnote + 6),VELOCITY);
      delayMicroseconds(1);
      noteOff(MIDICHANNEL1,(rootnote + 6),VELOCITY);
    }
    
    if(switchVar & 8 == smiley-cool
    {
      noteOn(MIDICHANNEL1,(rootnote + 7),VE
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