How to read unsigned char array from serial port?

Firmware
10

try this (complex) asynchronous approach:

// example packet: t123

const size_t PACKET_SIZE = 3;

template <class T> inline Print& operator <<(Print& obj, T arg)
{
  obj.print(arg);
  return obj;
}

char SENSOR_THr[3];

void setup()
{
  Serial.begin(9600);
  Serial << ("let's go!\n");
}

void loop()
{
  if (const char* newPacket = checkForNewPacket(Serial, 't'))
  {
    Serial << (F("Just Recieved:\t")) << newPacket[0] << "," << newPacket[1] << "," << newPacket[2] << "\n";
    for (size_t i = 0; i < PACKET_SIZE; i++) {
      SENSOR_THr[i] = newPacket[i];
    }
    for (auto i : SENSOR_THr) {
      Serial.print(i, HEX);
      Serial.print(",");
    }
    Serial.println();
  }
}

const char* checkForNewPacket(Stream& stream, const char startMarker)
{
  static char incomingPacket[PACKET_SIZE] = "";
  static bool gotStartMarker = false;
  static byte idx = 0;
  if (stream.available())
  {
    if (gotStartMarker) {
      incomingPacket[idx++] = stream.read();
      if (idx > sizeof(PACKET_SIZE)) {
        gotStartMarker = false;
        return incomingPacket;
      } else {
        return nullptr;
      }
    } else if (stream.peek() == startMarker) {
      idx = 0;
      gotStartMarker = true;
      (void) stream.read();
    } else {
      (void) stream.read();
    }
  }
  return nullptr;
}