Get and change HC-0X bluetooth module baudrate

BluetoothBaude.ino

#include <SoftwareSerial.h>

#define BT_Baud 57600
#define BT_BaudFallback 9600
#define BT_Cmd_Delay 2000 //1000 is okay, until HC-06-20190901

SoftwareSerial BT(8, 7);
long baud = 0;
uint8_t btVersion = 0xFF;

void setup() {
  Serial.begin(115200);
  InitializeBluetooth();
}

void loop() {
  bool received;
  while (BT.available()) {
    Serial.write(BT.read());
    received = true;
  }

  if (received) {
    received = false;
    Serial.println();
  }

  while (Serial.available())
  {
    char c = Serial.read();
    BT.write(c);
  }
}

void InitializeBluetooth() {
  GetBtVersion();
  //Uninitialized
  if (btVersion == 0xFF)
    FindBtModule();

  //Clear outgoing buffer
  BT.flush();
  //Clear incoming buffer
  BtDataAvailable();
}

bool FindBtModule() {
  Serial.println(F("BT Init"));
  delay(BT_Cmd_Delay);
  //First try with CarriageReturn/Linefeed. Otherwise the buffer might be filled with previous value
  btVersion = 3;
  baud = BtFindCurrentBaud();

  //Change Version to use delay(1000) without linebreak
  if (baud == 0L) {
    btVersion = 0;
    baud = BtFindCurrentBaud();
  }

  //Nothing found
  if (baud == 0L) {
    //Reset Version to uninitialized
    btVersion = 0xff;
    baud = BT_BaudFallback;
    //Try  with default value
    BT.begin(baud);
    Serial.println(F("BaudNotFound"));
    return false;
  }

  //Get Version to use lineend or delay
  if (BtGetVersion())
    SetBtVersion();

  //Clear incoming Buffer
  BtDataAvailable();

  //Baud not 57000
  if (baud != BT_Baud)
    if (!ChangeBtBaud()) {
      Serial.println(F("BaudNotChanged"));
      //Stay with found baud or default value
      if (baud == 0L)
        baud = BT_BaudFallback;
      BT.begin(baud);
      return false;
    }
  baud = BT_Baud;
  BT.begin(baud);
  return true;
}

long BtFindCurrentBaud() {
  static const long rates[] = { 4800, 9600, 19200, 38400, 57600, 115200 };
  uint8_t numRates = sizeof(rates) / sizeof(long);  //6
  //start with highest baud, to not buffer crap into HC-06
  //for (int rn = 0; rn < numRates; rn++) {
  for (int rn = numRates - 1; rn >= 0 ; rn--) {
    BT.begin(rates[rn]);
    BtDataAvailable();
    delay(200);
    PrintBtAt();
    BT.flush();
    if (btVersion >= 3)
      delay(100);
    else
      delay(BT_Cmd_Delay);  //No Linefeed, but 1Sec idle

    if (BtDataAvailable())
      return rates[rn];
  }
  return 0L;
}

// AT+BAUD<X> -> OK<X>
// X=4 : 9600bps (Default)
// X=6 : 38400bps
// X=7 : 57600bps
// X=8 : 115200bps
bool ChangeBtBaud() {
  Serial.println(F("BT ChangeBaud"));
  if (btVersion < 3)
    BT.print(F("AT+BAUD7"));
  if (btVersion == 3)
    BT.println(F("AT+UART=57600,0,0"));
  if (btVersion > 3)
    BT.println(F("AT+BAUD7"));
  delay(BT_Cmd_Delay);
  return BtDataAvailable();
}

void PrintBtAt() {
  if (btVersion >= 3)
    BT.println(F("AT"));
  else
    BT.print(F("AT"));
}

bool BtDataAvailable() {
  if (BT.available()) {
    //Read what´s on the buffer
    while (BT.available())
      BT.read();
    return true;
  }
  return false;
}

bool BtGetVersion() {
  if (btVersion != 0xFF)
    return BtGetVersion(btVersion >= 3);

  if (BtGetVersion(true))
    return true;
  delay(BT_Cmd_Delay);
  return BtGetVersion(false);
}

bool BtGetVersion(bool linebreak) {
  BT.print(F("AT+VERSION"));
  if (linebreak) {
    BT.println();
    delay(200);
  }
  else
    delay(BT_Cmd_Delay);
  char input[40];
  uint8_t j = 0;
  while (BT.available()) {
    if (j < sizeof(input))
      input[j++] = BT.read();
    else
      BT.read();

    //0 HC-06-20190901
    //1 ZS-040 (DX_smartv2.0)
    //2 FC-114 (hc01.comV2)
    //3 1744  (VERSION:3.0-20170609)
    //4 ZS-40 (Firmware V3.0.6,Bluetooth V4.0 LE)
    //4 BT05 (+VERSION=Firmware V3.0.6,Bluetooth V4.0 LE)

    if (input[0] == 'O' && input[1] == 'K') {
      btVersion = 1;
      return true;
    }
    if (input[0] == 'D' && input[1] == 'X') {
      btVersion = 1;
      return true;
    }
    if (input[8] == 'V' && input[9] == '2') {
      btVersion = 2;
      return true;
    }
    if (input[0] == 'H' && input[1] == 'C') {
      btVersion = 0;
      return true;
    }
    if (input[8] == '3' && input[10] == '0') {
      btVersion = 3;
      return true;
    }
    if (input[10] == '3' && input[27] == '4') {
      btVersion = 4;
      return true;
    }
    if (input[19] == '3' && input[36] == '4') {
      btVersion = 4;
      return true;
    }
  }
  if (j > sizeof(input) - 1)
    j = sizeof(input) - 1;
  input[j] = '\0';

  Serial.println(F("VersionNotFound"));
  return false;
}

void GetBtVersion() {
  //ToDo: get version from EEPROM
}
void SetBtVersion() {
  //ToDo: store version to EEPROM
}