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OP-Z unexpected MIDI demo project

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OP-Z MIDI one

And now for an unexpected demo…
… we are an engineering magazine, after all, so we wanted to create a bit of a crossover project to finish this review off. We grabbed one of our favourite MCUs – the SAME51-based ATMEL ATSAME51J19 and got to work!

We wanted to add a little OLED-based display to the OP-Z and use it for displaying the current beat inside the bar. We decided to use the MIDI protocol for this, as it gave us the necessary data out of the sequencer.

Using the USB-MIDI library we listen to start, stop and clock signals. As per the standard MIDI implementation, the OP-Z sends 24 clock pulses per quarter note. This means in order to get accurate beat sync we just need to count those pulses.

Sadly, there’s the little problem of the pulses being abour 20 ms apart. The core of the MCU absolutely has to be ready to receieve the pulse, and if it doesn’t – the entire thing gets out-of-sync. With some optimization, the M4 core had no issues keeping up – and we were left with a pretty sweet little project that we feel shows off how much is possible using just MIDI data.

GitHub Project Code
https://github.com/magazinMehatronika/MIDI-Beat-Tracker

#include <MIDI.h>
#include <SPI.h>
#include <Wire.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SH110X.h>

  #define BUTTON_A  9
  #define BUTTON_B  6
  #define BUTTON_C  5

using namespace midi;
MIDI_CREATE_DEFAULT_INSTANCE();

Adafruit_SH1107 display = Adafruit_SH1107(64, 128, &Wire);


int sync = 0;
int counter = 0;

int modeSel = 0;

bool enabler = false;

void setup()
{
    MIDI.begin(MIDI_CHANNEL_OMNI);  // Listen to all incoming messages

    delay(250); // wait for the OLED to power up
    display.begin(0x3C, true); // Address 0x3C default
    display.setRotation(1);

    
    display.clearDisplay();


    pinMode(BUTTON_A, INPUT_PULLUP);
    pinMode(BUTTON_B, INPUT_PULLUP);
    pinMode(BUTTON_C, INPUT_PULLUP);

}

void loop()
{

   digitalWrite(LED_BUILTIN, LOW);

  if(!digitalRead(BUTTON_A)) modeSel = 0;
  if(!digitalRead(BUTTON_B)) modeSel = 1;
  if(!digitalRead(BUTTON_C)) modeSel = 2;
   

   if(MIDI.read()){
            switch(MIDI.getType()){      // Get the type of the message we caught

            case Start:

            enabler = true;

            sync = 0;
            counter = 0;
            break;

            case Stop:

            enabler = false;

            display.clearDisplay();
            display.display();

            sync = 0;
            counter = 0;

            break;
            
            case Clock:
            if (enabler == true){
            
            if (sync == 0){

            switch (counter){

             case 0:
              display.clearDisplay();
              
              display.setTextSize(4,8);
              display.setTextColor(SH110X_WHITE);
              display.setCursor(0,0);

              switch(modeSel){
                case 0:
                display.print("One");
                break;
                case 1:
                display.print("Je'n");
                break;
                case 2:
                display.print("Ja--");
                break;
              }
              

              display.display();
              counter++;
              break;

              case 1:
              display.clearDisplay();


              display.setTextSize(4,8);
              display.setTextColor(SH110X_WHITE);
              display.setCursor(0,0);

              switch(modeSel){
                case 0:
                display.print("Two");
                break;
                case 1:
                display.print("Dva");
                break;
                case 2:
                display.print("--pa");
                break;
              }
              display.display();
              counter++;
              break;

              case 2:
              display.clearDisplay();

              display.setTextSize(4,8);
              display.setTextColor(SH110X_WHITE);
              display.setCursor(0,0);

              switch(modeSel){
                case 0:
                display.print("Three");
                break;
                case 1:
                display.print("Tri");
                break;
                case 2:
                display.print("pa--");
                break;
              }
              display.display();
              counter++;
              break;

              case 3:
              display.clearDisplay();

              display.setTextSize(4,8);
              display.setTextColor(SH110X_WHITE);
              display.setCursor(0,0);

              switch(modeSel){
                case 0:
                display.print("Four");
                break;
                case 1:
                display.print("Cet");
                break;
                case 2:
                display.print("--pa");
                break;
              }
              display.display();
              counter = 0;
              break;
              
            }
            
            digitalWrite(LED_BUILTIN, HIGH);
            delay(10);                // Wait for a second
            digitalWrite(LED_BUILTIN, LOW);
            sync = 24;
            }
            sync--;
            break;
           }

   }
   }
}
Dušan Dakić
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