Bass Pedal MIDI Controller Video

I’ve put together a short video showing the Bass Pedal project in its current state. Enjoy.

The next step will be to add voice control, so that I can shift it form the default piano voice and perhaps an LCD display panel showing the currently selected options. This could display the current octave, transpose setting, voice and volume.

Multi Button MIDI

I’ve now mixed the single button MIDI code with the I2C code to create a Multi Button MIDI. This is just the starting point but it works perfectly. Using the same board layout as the earlier post, upload this sketch and you’ll have sixteen inputs for your MIDI device, perfect for wiring into your Bass Pedal!

// MultiButtonMIDI.ino
// Driving MIDI using a Multiple Buttons
// Rob Ives 2012
// This code is released into the Public Domain.
 
#include <MIDI.h>
#include <Wire.h>
 
int keyispressed[16]; //Is the key currently pressed?
int noteisplaying[16]; //Is the Note currently playing?
unsigned char data1; //data from chip 1
unsigned char data2; //data from chip 2
 
void  setup() //The Setup Loop
{
  Wire.begin(); // setup the I2C bus
  for (unsigned int i = 0; i < 16; i++) { //Init variables
    keyispressed[i] = 1; //clear the keys array (High is off)
    noteisplaying[i] = 0; //no notes are playing
  }
  MIDI.begin(); //initialise midi library
}
//---------------------------------------------
void loop() //the main loop
{
  readkeys();
  sendMIDI();
}  
//-------------------------------------
void readkeys() { //Read the state of the I2C chips. 1 is open, 0 is closed.
  Wire.requestFrom(0x38, 1); // read the data from chip 1 in data1
  if (Wire.available()){
     data1 = Wire.read(); 
 
  }
  Wire.requestFrom(0x39, 1); // read the data freom chip 2 into data2
  if (Wire.available()){
     data2 = Wire.read();    
  }
 
  for (unsigned char i = 0; i < 8; i++) {// puts data bits from chip 1 into keys array
       keyispressed[i] = ((data1 >> i) & 1); // set the key variable to the current state. chip 1
       keyispressed[i + 8] = ((data2 >> i) & 1); //chip 2
  }
}  
//-------------------------------------
void sendMIDI() { // Send MIDI instructions via the MIDI out
  for (unsigned char i = 0; i < 16; i++) { //for each note in the array
    if (keyispressed[i] == LOW){ //the key on the board is pressed 
      if(!noteisplaying[i]){ //if the note is not already playing send MIDI instruction to start the note
         MIDI.sendNoteOn(36+i,127,1);  // Send a Note ( vel.127  ch. 1)
         noteisplaying[i] = 1; // set the note playing flag to TRUE
      }
    }
    else{
      if(noteisplaying[i]){ //if the note is currently playing, turn it off
        MIDI.sendNoteOff(36+i,0,1);   // Stop the note
        noteisplaying[i] = 0; // clear the note is playing flag
      }
    }
  }
}

This is just the start. My next step will be to add a volume control and an octave switch.
Possible plan for octave switch: Two foot buttons, one for up, one for down, Four LEDs showing which octave is currently selected.

Testing the I2C bus

I’m using the I2C bus to read the keys in from the bass pedal. The breadboard layout is shown in an earlier post. To make sure that everything is working properly with the chips I have set up a piece of code that will read the sixteen pins in I2C chips and display their output via the Arduino serial monitor.
The code is here:

// MultiButtonTest.ino
// Driving MIDI using a Multiple Buttons
// Rob Ives 2012
// This code is released into the Public Domain.
 
#include <MIDI.h>
#include <Wire.h>
 
int keyispressed[16]; //Variable. Is the key currently pressed?
int noteisplaying[16]; //Variable. Is the Note currently playing?
unsigned char data1; //data from chip 1
unsigned char data2; //data from chip 2
 
void  setup() //The Setup Loop
{
  Wire.begin(); // setup the I2C bus
  Serial.begin(9600); // serial set up for debugging
  for (unsigned int i = 0; i < 16; i++) { 
    keyispressed[i] = 1; //clear the keys array (High is off)
    noteisplaying[i] = 0; //no notes are playing
  }
 
  //MIDI.begin(); //initialise midi library
}
//---------------------------------------------
void loop() //the main loop
{
  readkeys();
  displaykeys();
}  
//-------------------------------------
void readkeys() {
  Wire.requestFrom(0x38, 1); // read the data from chip 1 into data1
  if (Wire.available()){
     data1 = Wire.read(); 
 
  }
  Wire.requestFrom(0x39, 1); // read the data freom chip 2 into data2
  if (Wire.available()){
     data2 = Wire.read();    
  }
 
  for (unsigned char i = 0; i < 8; i++) {// puts data bits from chip 1 into keys array
       keyispressed[i] = ((data1 >> i) & 1); // set the key variable to the current state. chip 1
       keyispressed[i + 8] = ((data2 >> i) & 1); //chip 2
  }
}  
//-------------------------------------
void displaykeys() { //Display the keys presssed for debugging purposes
  for (unsigned char i = 0; i < 16; i++) {
    Serial.print(keyispressed[i]); //print out each value from the array on one line.
  } 
  Serial.println("<<"); 
}

Wire up the chip and run the sketch.

In the Arduino environment on your computer go to Tools -> Serial Monitor
where you should see a display spitting out rows of sixteen ones over and over.
Try connecting each of the data pins on the I2C chips to ground and if all is well, the corresponding one will turn to a zero.

Pullup / Pulldown

Next step in the midification process is to add the PCF8574 chips. These chips let me add multiple inputs using only three of the input lines on the Arduino. The chips can be daisy-chained together using the same three input lines so with two chips I can have sixteen inputs and still have loads in inputs/outputs available on the arduino for other interesting stuff.
Checking the data sheet for the chip I noticed that the i/o lines on the chip have a built in pullup resistor. This means that if the input line is not connected it will be at the high voltage. To close a switch the input line it needs to be connected to the ground line.
In my previous, single switch, set up I had used a pulldown resistor meaning that an open input was at zero volts and needed five volts to be a closed input.
The diagram below shows a pullup resistor in place.

With the switch open Vout will be high. When the switch is closed it goes low.
For consistency I have changed the circuit and code on the single switch project to use a pullup resistor.

This has been simply a case of swapping the resistor and the wire.
The code is modified very slightly as well changing the line

if (keyispressed == HIGH){ //the key on the board is pressed

to

if (keyispressed == LOW){ //the key on the board is pressed

//Driving MIDI using a single button
// Rob Ives 2012
// This code is released into the Public Domain.
 
#include 
 
#define KEY 8
#define LED 13
 
int keyispressed = 0; //Variable. Is the key currently pressed?
int noteisplaying = 0; //Variable. Is the Note currently playing?
 
void  setup() //The Setup Loop
{
  pinMode(LED, OUTPUT);  //Set pin 13 , the led, to output
  pinMode(KEY, INPUT);  //Set pin 8 to input to detect the key press
  MIDI.begin(); //initialise midi library
}
//---------------------------------------------
void loop() //the main loop
{
  keyispressed = digitalRead(KEY); //read pin 8
 
  if (keyispressed == LOW){ //the key on the board is pressed
    digitalWrite(LED, HIGH); //set the LED to on. 
    if(!noteisplaying){ //if the note is not already playing send MIDI instruction to start
       MIDI.sendNoteOn(36,127,1);  // Send a Note (pitch 36 (C2), vel.127  ch. 1)
       noteisplaying = 1; // set the note playing flag to TRUE
    }
  }
  else{
    digitalWrite(LED,LOW); // the key is not pressed. Turn off the LED
    if(noteisplaying){ //if the note is currently playing, turn it off
      MIDI.sendNoteOff(36,0,1);   // Stop the note
      noteisplaying = 0; // clear the note is playing flag
    }
  }
}

The good news is that it still works. Time for more inputs