const int sides=2;

void setup() {
  Serial.begin(115200);
  Serial.print("Hit Enter to roll a d");
  Serial.println(sides);
}

void loop() {
  while (Serial.available()) {
    int ch = Serial.read();
    if (ch == '\n') {
    randomSeed(random() + micros()); // Add entropy from keypress
    Serial.print(random(1, sides+1));
    Serial.print(',');
    }
  }
}