programa:

void setup() {
  pinMode(2, INPUT_PULLUP);
  pinMode(3, INPUT_PULLUP);
  pinMode(4, INPUT_PULLUP);
  pinMode(5, INPUT_PULLUP);
  pinMode(6, INPUT_PULLUP);
  pinMode(7, INPUT_PULLUP);
 
  Keyboard.begin();
}

void loop() {
 
  if(digitalRead(2)==LOW){
    //Send an ASCII 'A',
    Keyboard.write(65);
  }
 
  if(digitalRead(3)==LOW){
    //Send an ASCII 'B',
    Keyboard.write(66);
    }
    
    if(digitalRead(4)==LOW){
    //Send an ASCII 'C',
    Keyboard.write(67);
    }
    
    if(digitalRead(5)==LOW){
    //Send an ASCII 'D',
    Keyboard.write(68);
    }
    
    if(digitalRead(6)==LOW){
    //Send an ASCII 'E',
    Keyboard.write(69);
    }
    
    if(digitalRead(7)==LOW){
    //Send an ASCII 'F',
    Keyboard.write(70);
}