Keyboard matrix beginnerish help (keypad library)

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Take a look at my MIDI Controller library. It supports keyboard matrices like that directly, just specify the pins, and the notes, and it sends out MIDI Note On/Off events (over USB/Serial/Debug, you name it).

MIDI_controller/Ex.11.Button-Matrix.ino at master · tttapa/MIDI_controller · GitHub (Documentation)

/*
This is an example of the "ButtonMatrix" class of the MIDI_controller library.
Connect a 4 × 3 matrix of buttons with the rows to pins 2, 3, 4 and 5, 
and the columns to pins 6, 7 and 8.
Pull-up resistors are not necessary, because the internal ones will be used. 
If you want to be able to press multiple buttons at once, add a diode 
in series with each button, as shown in the schematic on the Wiki:
https://github.com/tttapa/MIDI_controller/wiki/Hardware
The note numbers are specified in the 'addresses' array.
Map accordingly in your DAW or DJ software.
Written by tttapa, 24/09/2017
https://github.com/tttapa/MIDI_controller
*/

#include "MIDI_Controller.h" // Include the library

const uint8_t velocity = 0b1111111; // Maximum velocity (0b1111111 = 0x7F = 127)
const uint8_t addresses[4][3] = {   // the note numbers corresponding to the buttons in the matrix
  {  1,  2,  3 },
  {  4,  5,  6 },
  {  7,  8,  9 },
  { 10, 11, 12 }
};

// Create a new instance of the class 'ButtonMatrix', called 'buttonmatrix', with dimensions 4 rows and 3 columns, with the rows connected to pins 2, 3, 4 and 5
// and the columns connected to pins 6, 7 and 8, that sends MIDI messages with the notes specified in 'addresses' on MIDI channel 1, with velocity 127
ButtonMatrix<4, 3> buttonmatrix({2, 3, 4, 5}, {6, 7, 8}, addresses, 1, velocity);

void setup() {}

void loop() {
  // Refresh the buttons (check whether the states have changed since last time, if so, send it over MIDI)
  MIDI_Controller.refresh();
}

Here's the diagram for the example:

582×868 20.7 KB

You can flip the rows and collumns, but you have to change both the code and the schematic if you do that.

Pieter