   case '7': speed = 7; break;
   case '8': speed = 8; break;
   case '9': speed = 9; break;
+  default : return;
   }
+  ack();
+}
+
+void ack() {
+  delay(200);
+  digitalWrite(RELAY_PIN, RELAY_ON);
+  delay(2000);
+  digitalWrite(RELAY_PIN, RELAY_OFF);
+  delay(200);
 }
 
 void wait() {

void setup() {
  Serial.begin(SERIAL_BAUD);
  pinMode(RELAY_PIN, OUTPUT);

  digitalWrite(RELAY_PIN, RELAY_ON);
  delay(2000);
  digitalWrite(RELAY_PIN, RELAY_OFF);
}

void loop() {

#define RELAY_ON  LOW
#define RELAY_OFF HIGH

#define TIME_WAIT  3000
#define TIME_ON    500
#define TIME_OFF   300
#define TIME_DOT   500
#define TIME_DASH  1000
#define TIME_MORSE 300

#define SEQ_WAIT  "w"
#define SEQ_BLINK "b"
