// MCU BASIC: https://www.basic4mcu.com
// DateTime : 2018-08-06 오후 4:47:50
// by Ok-Hyun Park
//
//record,playback
#include <SoftwareSerial.h>
SoftwareSerial mySerial(2,3);
//
int ledPin=13;
int resetMIDI=4;
int btn1=13,btn2=12,btn3=11,btn4=10,
#define btn12 A2 //recording
#define btn13 A1 //replay
//
byte note=0;
boolean bs1=0,bs2=0,bs3=0,bs4=0,bs12=0,bs13=0;
boolean br1=0,br2=0,br3=0,br4=0,br12=0,br13=0;
int bn1=60,bn2=62,bn3=64,bn4=65; //버튼1  도 //버튼2  레 //버튼3  미 //버튼4  파
int patch=0;
byte byteData;
//
void setup(){
  Serial.begin(31250);
  mySerial.begin(31250);
  pinMode(resetMIDI,OUTPUT);  digitalWrite(resetMIDI,LOW ); delay(100); digitalWrite(resetMIDI,HIGH); delay(100);
  pinMode(btn1,INPUT_PULLUP); pinMode(btn2 ,INPUT_PULLUP);  pinMode(btn3 ,INPUT_PULLUP);
  pinMode(btn4,INPUT_PULLUP); pinMode(btn12,INPUT_PULLUP);  pinMode(btn13,INPUT_PULLUP);
}
//
void loop(){
  br1=digitalRead(btn1); br2 =digitalRead(btn2 ); br3=digitalRead(btn3);
  br4=digitalRead(btn4); br12=digitalRead(btn12); br13=digitalRead(btn13);
  //
  if(!bs1&&!br1){ noteOn(0,bn1,100); bs1=true; } else if(bs1&&br1){ noteOff(0,bn1,0); bs1=false; }
  if(!bs2&&!br2){ noteOn(0,bn2,100); bs2=true; } else if(bs2&&br2){ noteOff(0,bn2,0); bs2=false; }
  if(!bs3&&!br3){ noteOn(0,bn3,100); bs3=true; } else if(bs3&&br3){ noteOff(0,bn3,0); bs3=false; }
  if(!bs4&&!br4){ noteOn(0,bn4,100); bs4=true; } else if(bs4&&br4){ noteOff(0,bn4,0); bs4=false; }
  if(!bs12&&!br12){}
  if(!bs13&&!br13){}
  if(Serial.available()>0){ byteData=Serial.read(); mySerial.write(byteData); }
}
//
void noteOn (byte channel,byte note,byte attack_velocity ){ talkMIDI((0x90|channel),note,attack_velocity ); }
void noteOff(byte channel,byte note,byte release_velocity){ talkMIDI((0x80|channel),note,release_velocity); }
//
void talkMIDI(byte cmd,byte data1,byte data2){
  digitalWrite(ledPin,HIGH);
  mySerial.write(cmd); mySerial.write(data1); if((cmd&0xF0)<=0xB0)mySerial.write(data2);
  digitalWrite(ledPin,LOW);
}
 
질문 소스를 정리해서 올린겁니다.
원하는대로 기능을 넣는 것은 차차 만들어보죠
음색 버튼은 도레미파 4개만 사용할건가요?