program4.ino

#include <SoftwareSerial.h>

//--- Begin Pin Declarations ---//
const byte HC12RxdPin = 4;  // "RXD" Pin on HC12
const byte HC12TxdPin = 5;  // "TXD" Pin on HC12
const byte HC12SetPin = 6;  // "SET" Pin on HC12
const byte GPSTxdPin = 7;   // "TXD" on GPS (if available)
const byte GPSRxdPin = 8;   // "RXD" on GPS
//--- End Pin Declarations ---//

//--- Begin variable declarations ---//
char GPSbyteIn;          // Temporary variable
String GPSBuffer3 = "";  // Read/Write Buffer 3 -- GPS

boolean debug = false;
boolean HC12End = false;      // Flag for End of HC12 String
boolean GPSEnd = false;       // Flag for End of GPS String
boolean commandMode = false;  // Send AT commands to remote receivers
//--- End variable declarations ---//

// Create Software Serial Ports for HC12 & GPS
// Software Serial ports Rx and Tx are opposite the HC12 Rxd and Txd
SoftwareSerial HC12(HC12TxdPin, HC12RxdPin);
SoftwareSerial GPS(GPSRxdPin, GPSTxdPin);

void setup() {
  buffer3.reserve(82);  // Reserve 82 bytes for longest NMEA sentence

  pinMode(HC12SetPin, OUTPUT);     // Output High for Transparent / Low for Command
  digitalWrite(HC12SetPin, HIGH);  // Enter Transparent mode
  delay(80);                       // 80 ms delay before operation per datasheet
  HC12.begin(4800);                // Open software serial port to HC12
  GPS.begin(9600);                 // Open software serial port to GPS
  GPS.listen();

  // --- Begin One-Time HC12 Auto-Configuration ---
  digitalWrite(HC12SetPin, LOW);  // Enter command mode
  delay(100);                     // Wait for HC12 to settle
  HC12.println("AT+RX");          // Example AT command
  delay(200);                     // Wait for reply

  while (HC12.available()) {
    Serial.write(HC12.read());  // Print HC12's response to serial monitor
  }

  digitalWrite(HC12SetPin, HIGH);  // Return to transparent mode
  delay(100);                      // Wait for HC12 to stabilize
  // --- End Auto-Configuration ---
}

void loop() {
  while (GPS.available()) {
    byteIn = GPS.read();
    buffer3 += char(byteIn);
    if (byteIn == '\n') {
      GPSEnd = true;
    }
  }

  if (GPSEnd) {
    // GPRMC, GPVTG, GPGGA, GPGSA, GPGSV, GPGLL
    if (buffer3.startsWith("$GPRMC") || buffer3.startsWith("$GPGGA") || buffer3.startsWith("$GPGLL")) {
      HC12.print(buffer3);  // Transmit RMC, GGA, and GLL sentences
      buffer3 = "";         // Clear buffer
    } else {
      buffer3 = "";  // Delete GSA, GSV, VTG sentences
    }
    GPSEnd = false;  // Reset GPS flag
  }
}