Hi A7
I didnt even made one attempt to connect the start/stop switch and button to the board because i simply do not know how to start. 
Below is the drawing like a have the 16 standard buttons now. They work perfectly btw, already test it.
Here is the code that i'm using. I know it's messy. Probably a lot of stuff in it that i do not nood. But i took this one from the internet and tryed to adjust it myself. I'm still new at all of this 
#include <Key.h>
#include <Keypad.h>
#include <Joystick.h>
#define ENABLE_PULLUPS
#define NUMROTARIES 4
#define NUMBUTTONS 16
#define NUMROWS 4
#define NUMCOLS 4
byte buttons[NUMROWS][NUMCOLS] = {
{ 0, 1, 2, 3 },
{ 4, 5, 6, 7 },
{ 8, 9, 10, 11 },
{ 12, 13, 14, 15 },
};
struct rotariesdef {
byte pin1;
byte pin2;
int ccwchar;
int cwchar;
volatile unsigned char state;
};
rotariesdef rotaries[NUMROTARIES]{
{ 0, 1, 24, 25, 0 },
{ 2, 3, 26, 27, 0 },
{ 4, 5, 28, 29, 0 },
{ 6, 7, 30, 31, 0 },
};
#define DIR_CCW 0x10
#define DIR_CW 0x20
#define R_START 0x0
#ifdef HALF_STEP
#define R_CCW_BEGIN 0x1
#define R_CW_BEGIN 0x2
#define R_START_M 0x3
#define R_CW_BEGIN_M 0x4
#define R_CCW_BEGIN_M 0x5
const unsigned char ttable[6][4] = {
// R_START (00)
{ R_START_M, R_CW_BEGIN, R_CCW_BEGIN, R_START },
// R_CCW_BEGIN
{ R_START_M | DIR_CCW, R_START, R_CCW_BEGIN, R_START },
// R_CW_BEGIN
{ R_START_M | DIR_CW, R_CW_BEGIN, R_START, R_START },
// R_START_M (11)
{ R_START_M, R_CCW_BEGIN_M, R_CW_BEGIN_M, R_START },
// R_CW_BEGIN_M
{ R_START_M, R_START_M, R_CW_BEGIN_M, R_START | DIR_CW },
// R_CCW_BEGIN_M
{ R_START_M, R_CCW_BEGIN_M, R_START_M, R_START | DIR_CCW },
};
#else
#define R_CW_FINAL 0x1
#define R_CW_BEGIN 0x2
#define R_CW_NEXT 0x3
#define R_CCW_BEGIN 0x4
#define R_CCW_FINAL 0x5
#define R_CCW_NEXT 0x6
const unsigned char ttable[7][4] = {
// R_START
{ R_START, R_CW_BEGIN, R_CCW_BEGIN, R_START },
// R_CW_FINAL
{ R_CW_NEXT, R_START, R_CW_FINAL, R_START | DIR_CW },
// R_CW_BEGIN
{ R_CW_NEXT, R_CW_BEGIN, R_START, R_START },
// R_CW_NEXT
{ R_CW_NEXT, R_CW_BEGIN, R_CW_FINAL, R_START },
// R_CCW_BEGIN
{ R_CCW_NEXT, R_START, R_CCW_BEGIN, R_START },
// R_CCW_FINAL
{ R_CCW_NEXT, R_CCW_FINAL, R_START, R_START | DIR_CCW },
// R_CCW_NEXT
{ R_CCW_NEXT, R_CCW_FINAL, R_CCW_BEGIN, R_START },
};
#endif
byte rowPins[NUMROWS] = {
21,
20,
19,
18,
};
byte colPins[NUMCOLS] = {
14,
15,
16,
10,
};
Keypad buttbx = Keypad(makeKeymap(buttons), rowPins, colPins, NUMROWS, NUMCOLS);
Joystick_ Joystick(JOYSTICK_DEFAULT_REPORT_ID,
JOYSTICK_TYPE_JOYSTICK, 32, 0,
false, false, false, false, false, false,
false, false, false, false, false);
void setup() {
Joystick.begin();
rotary_init();
}
void loop() {
CheckAllEncoders();
CheckAllButtons();
}
void CheckAllButtons(void) {
if (buttbx.getKeys()) {
for (int i = 0; i < LIST_MAX; i++)
if (buttbx.key[i].stateChanged) {
switch (buttbx.key[i].kstate) {
case PRESSED:
case HOLD:
Joystick.setButton(buttbx.key[i].kchar, 1);
break;
case RELEASED:
case IDLE:
Joystick.setButton(buttbx.key[i].kchar, 0);
break;
}
}
}
}
void rotary_init() {
for (int i = 0; i < NUMROTARIES; i++) {
pinMode(rotaries[i].pin1, INPUT);
pinMode(rotaries[i].pin2, INPUT);
#ifdef ENABLE_PULLUPS
digitalWrite(rotaries[i].pin1, HIGH);
digitalWrite(rotaries[i].pin2, HIGH);
#endif
}
}
unsigned char rotary_process(int _i) {
unsigned char pinstate = (digitalRead(rotaries[_i].pin2) << 1) | digitalRead(rotaries[_i].pin1);
rotaries[_i].state = ttable[rotaries[_i].state & 0xf][pinstate];
return (rotaries[_i].state & 0x30);
}
void CheckAllEncoders(void) {
for (int i = 0; i < NUMROTARIES; i++) {
unsigned char result = rotary_process(i);
if (result == DIR_CCW) {
Joystick.setButton(rotaries[i].ccwchar, 1);
delay(50);
Joystick.setButton(rotaries[i].ccwchar, 0);
};
if (result == DIR_CW) {
Joystick.setButton(rotaries[i].cwchar, 1);
delay(50);
Joystick.setButton(rotaries[i].cwchar, 0);
};
}
}
I also added a picture from the back of the start/stop switch.
