ArduinoController

#include <FastLED.h>
#define LED_PIN     7
#define NUM_LEDS    100

CRGB leds[NUM_LEDS];

String inputString = "";
bool stringComplete = false;
char inChar = ' ';

int phase = 0;

void setup() {
  pinMode(13, OUTPUT);
  pinMode(9, OUTPUT);
  Serial.begin(250000);
  FastLED.addLeds<WS2812, LED_PIN, GRB>(leds, NUM_LEDS);

  for (int l = 0; l < NUM_LEDS; l++) {
    leds[l] = CRGB(100, 0, 0);
  }
  FastLED.show();

  inputString.reserve(200);
}

void loop() {
  if (phase == 0) {
    if (inChar == 'a') {
      phase = 1;
      return;
    }
    digitalWrite(13, HIGH);
    delay(100);
    digitalWrite(13, LOW);
    delay(100);
  }
  if (phase == 1) {
    Serial.write('b');
    phase = 2;
  }
  if (phase == 2) {
    if (inChar == 'c') {
      Serial.write('d');
      digitalWrite(13, HIGH);
      phase = 3;
      return;
    }
    digitalWrite(13, HIGH);
    delay(50);
    digitalWrite(13, LOW);
    delay(50);
  }
  if (phase == 3) {
    if (stringComplete) {
      int red = 0, green = 0, blue = 0;
      int off = 0;
      for (int l = 0; l < NUM_LEDS; l += 2) {
        red = unhex(inputString.charAt(off), inputString.charAt(off + 1));
        green = unhex(inputString.charAt(off + 2), inputString.charAt(off + 3));
        blue = unhex(inputString.charAt(off + 4), inputString.charAt(off + 5));
        leds[l] = leds[l + 1] = CRGB(red, green, blue);
        off += 6;
      }

      FastLED.show();
      Serial.println(inputString);
      inputString = "";
      stringComplete = false;
    }
  }

}

int unhex(char a, char b) {
  int result = 0;
  int ai = (int) a, bi = (int) b;

  if (ai >= 48 && ai <= 57) result = (ai - 48) * 16;
  else if (ai >= 65 && ai <= 70) result = (ai - 55) * 16;

  if (bi >= 48 && bi <= 57) result += (bi - 48);
  else if (bi >= 65 && bi <= 70) result += (bi - 55);

  return result;
}

void serialEvent() {
  while (Serial.available()) {
    inChar = (char)Serial.read();
    inputString += inChar;
    if (inChar == 'x') {
      stringComplete = true;
      Serial.println("Recieved!");
    }
  }
  digitalWrite(9, HIGH);
  delay(100);
  digitalWrite(9, LOW);
}