saklar sms arduino

#include <gprs.h>
#include <softwareserial.h>

/*koneksi sim800 dengan Arduino
SIM800 TX is connected to Arduino D8
SIM800 RX is connected to Arduino D7
*/

#define TIMEOUT    5000
#define RELAY_PIN    0 // relay pin di hubungkan ke D0

bool relayStatus;
GPRS gprs;

void setup() {
  Serial.begin(9600);
  while (!Serial);

  Serial.println("Starting SIM800 SMS Command Processor");
  gprs.preInit();
  delay(1000);

  while (0 != gprs.init()) {
    delay(1000);
    Serial.print("init error\r\n");
  }

  //Set SMS mode ke mode ASCII
  if (0 != gprs.sendCmdAndWaitForResp("AT+CMGF=1\r\n", "OK", TIMEOUT)) {
    ERROR("ERROR:CNMI");
    return;
  }

  //mulai baca ada indikasi sms baru
  if (0 != gprs.sendCmdAndWaitForResp("AT+CNMI=1,2,0,0,0\r\n", "OK", TIMEOUT)) {
    ERROR("ERROR:CNMI");
    return;
  }

  Serial.println("Init success");
}

//Variable penyimpanan sms
char currentLine[500] = "";
int currentLineIndex = 0;

bool nextLineIsMessage = false;

void loop() {
  //kontrol status relay di sini
  digitalWrite(RELAY_PIN, relayStatus);

  //jika ada data serial terbaca
  if (gprs.serialSIM800.available()) {
    char lastCharRead = gprs.serialSIM800.read();
    //baca karakter dari serial
    if (lastCharRead == '\r' || lastCharRead == '\n') {
      String lastLine = String(currentLine);

      //jika baris terakhir adalah +CMT, ada indikasi sms baru masuk.
      if (lastLine.startsWith("+CMT:")) {

        Serial.println(lastLine);
        nextLineIsMessage = true;

      } else if (lastLine.length() > 0) {

        if (nextLineIsMessage) {
          Serial.println(lastLine);

          //disini tempat pembacaan sms oleh sim800, kontrol sms ada disini
          if (lastLine.indexOf("RELAY ON") >= 0) {
            relayStatus = 1;
          } else if (lastLine.indexOf("RELAY OFF") >= 0) {
            relayStatus = 0;
          }

          nextLineIsMessage = false;
        }

      }

      //Clear char array for next line of read
      for ( int i = 0; i < sizeof(currentLine);  ++i ) {
        currentLine[i] = (char)0;
      }
      currentLineIndex = 0;
    } else {
      currentLine[currentLineIndex++] = lastCharRead;
    }
  }
}