Serial bytes received by Arduino different than that sent

Projects Programming
1

I am using the HC-05 bluetooth module to connect to my Arduino mega. I am sending messages of 35 bytes using the library pySerialTransfer / SerialTransfer.h.

These are the bytes my python module logs as sending:

ARDUINO: b'\x01\x88\x13\xc8\xaf\x00\x00\x00\x00\x9f\x05\x1e\x00UAL2380\x00\x00SFO-HNL\x00\x00\x00\x00\x00\x00'

These are the bytes the Arduino records as receiving:

Recd 35 new bytes: 1|FFFFFF88|13|FFFFFFC8|FFFFFFAF|0|0|0|0|FFFFFF9F|5|1E|0|55|41|4C|32|33|38|30|0|0|53|46|4F|2D|48|4E|4C|0|0|0|0|0|0|

Everything matches exactly.... except the extra data in bytes 2, 4, 5 and 10 - what might be causing that?

Here's the python code:

def Write(link, values, format_string):
  """Sends the encapsulated string command on an open pySerialTransfer."""
  packed_bytes = struct.pack(format_string, *values)
  Log(packed_bytes)
  for n, b in enumerate(packed_bytes):
    link.txBuff[n] = b
  link.send(len(packed_bytes))

The format_string is '=?hlhhh9s9shh'.

Here's the Arduino code that receives the data / prints the bytes-received message:

void PrintRecdBytes(int bytes_read, char* rx_buff) {
  Serial.print("Recd ");
  Serial.print(bytes_read);
  Serial.print(" new bytes: ");
  for(byte i = 0; i < bytes_read; i++) {
    Serial.print(rx_buff[i], HEX);
    Serial.print("|");
  }
  Serial.println("");
}

void Read() {
  long now = millis();
  bool bt_available = bluetooth.available();
  if (now - last_read_time >= READ_DELAY_SECONDS * 1000 && bt_available) {
    bluetooth.rxObj(inbound, sizeof(inbound));
    last_read_time = now;
    if (VERBOSE) {
      PrintRecdBytes(bluetooth.bytesRead, bluetooth.rxBuff);
    }
  }
}

Thanks for any guidance!

2 
void PrintRecdBytes(int bytes_read, char* rx_buff) {

Try with

void PrintRecdBytes(int bytes_read, byte* rx_buff) {

Char is signed -127 to 127. You are seeing sign extension with the char with rollover to negative values.

3

That did the trick - thank you very much!