#define K13_PIN 10
#define K12_PIN 16
#define K11_PIN 14
#define AC_PIN   3

void setup() {
	pinMode(K13_PIN, OUTPUT);
	pinMode(K12_PIN, OUTPUT);
	pinMode(K11_PIN, OUTPUT);
	pinMode(AC_PIN,  OUTPUT);
}

void loop() {
	digitalWrite(K12_PIN, HIGH); delay(10);
	digitalWrite(K12_PIN, LOW);  delay(1000);
	digitalWrite(K13_PIN, HIGH); delay(10);
	digitalWrite(K13_PIN, LOW);  delay(1000);
	digitalWrite(K11_PIN, HIGH); delay(10);
	digitalWrite(K11_PIN, LOW);  delay(1000);
	digitalWrite(AC_PIN,  HIGH); delay(10);
	digitalWrite(AC_PIN,  LOW);  delay(1000);
}

$ pio run -t upload

void push_key(unsigned char key) {
  switch(key) {
    case '0':
      digitalWrite(K13_PIN, HIGH);
      delay(10);
      digitalWrite(K13_PIN, LOW);
      break;
  ......
}
void setup() {
  Serial.begin(19200);
  pinMode(K13_PIN, OUTPUT);
  ......
}
void loop() {
  int key;
  key = Serial.read();
  if ( key != -1 ) push_key((unsigned char)key);
  delay(100);
}