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How to decode Bluetooth LE Package / Frame / Beacon from FreeTec PX-1737-919 Bluetooth 4.0 Temperature Sensor?

The sensor advertises these Bluetooth LE packages:

> 04 3E 26 02 01 03 01 B8 AB C0 5D 4C D9 1A 02 01 04 09 09 38 
  42 42 41 43 34 39 44 07 16 09 18 47 08 00 FE 04 16 0F 18 5B 
  B3 
> 04 3E 26 02 01 03 01 B8 AB C0 5D 4C D9 1A 02 01 04 09 09 38 
  42 42 41 43 34 39 44 07 16 09 18 45 08 00 FE 04 16 0F 18 5A 
  BC 
> 04 3E 26 02 01 03 01 B8 AB C0 5D 4C D9 1A 02 01 04 09 09 38 
  42 42 41 43 34 39 44 07 16 09 18 44 08 00 FE 04 16 0F 18 5B 
  B2

How to decode it?

LE Advertising Report:

  ADV_NONCONN_IND - Non connectable undirected advertising (3)
  bdaddr D9:4C:5D:C0:AB:B8 (Random)
  Flags: 0x04
  Complete local name: '8BBAC49D'
  Unknown type 0x16 with 6 bytes data
  Unknown type 0x16 with 3 bytes data
  RSSI: -77
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3 answers

This is not a beacon advertisement. Packets are a device that sends three pieces of information.

  • The local device name is "8BBAC49D"
  • Health thermometer service available (with current temperature measurement)
  • Battery service available (with current battery level measurement)

Detection of a detected BLE packet:

> 04 3E 26 02 01 03 01 B8 AB C0 5D 4C D9 1A 02 01 04 09 09 38 
  42 42 41 43 34 39 44 07 16 09 18 44 08 00 FE 04 16 0F 18 5B 
  B2

, , , .

:

B8 AB C0 5D 4C D9 1A # Bluetooth Mac Address
02 # Number of bytes that follow in first AD structure
01 # Flags AD type
04 # Flags value 0x04 = 000000100  
   bit 0 (OFF) LE Limited Discoverable Mode
   bit 1 (OFF) LE General Discoverable Mode
   bit 2 (ON) BR/EDR Not Supported
   bit 3 (OFF) Simultaneous LE and BR/EDR to Same Device Capable (controller)
   bit 4 (OFF) Simultaneous LE and BR/EDR to Same Device Capable (Host)
09 # Number of bytes that follow in the first AD Structure
09 # Complete Local Name AD Type
38 42 42 41 43 34 39 44 # "8BBAC49D"
07 # Number of bytes that follow in the second AD Structure
16 # Service Data AD Type
09 18 # 16-bit Service UUID 0x1809 = Health thermometer (org.bluetooth.service.health_thermometer)
44 08 00 FE # Additional Service Data 440800  (Temperature = 0x000844 x 10^-2) = 21.16 degrees
04 # Number of bytes that follow in the third AD Structure
16 # Service Data AD Type
0F 18 # 16-bit Service UUID 0x180F  = Battery Service (org.bluetooth.service.battery_service) 
5B # Additional Service Data (battery level)
B2 # checksum

. UUID 16- Bluetooth:

https://developer.bluetooth.org/gatt/services/Pages/ServiceViewer.aspx?u=org.bluetooth.service.battery_service.xml

https://developer.bluetooth.org/gatt/services/Pages/ServiceViewer.aspx?u=org.bluetooth.service.health_thermometer.xml

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hcidump -w dump.log Wireshark - .

:

04 # HCI Packet Type: HCI Event (0x04)
3E # Event Code: LE Meta (0x3e)
26 # Parameter Total Length: 38
02 # Sub Event: LE Advertising Report (0x02)
01 # Num Reports: 1
03 # Event Type: Non-Connectable Undirected Advertising (0x03)
01 # Peer Address Type: Random Device Address (0x01)

Wireshark: Wireshark

- btsnoop.log. Wireshark hcidump -r packet.log.

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  public class Util {

public static int convertU16ToInt(byte i) {
    int firstByte = (0x000000FF & ((int)i));
    return firstByte;
}

public static int bytesToInt(final byte[] array, final int start)
{
    final ByteBuffer buf = ByteBuffer.wrap(array); // big endian by default
    buf.position(start);
    buf.put(array);
    buf.position(start);
    return buf.getInt();
}

public static int convertU32ToInt(byte b[], int start) {
    return ((b[start] << 24) & 0xff000000 |(b[start + 1] << 16) & 0xff0000
            | (b[start + 2] << 8) & 0xff00 | (b[start + 3]) & 0xff);
}
public static long int64Converter(byte buf[], int start) {
    return ((buf[start] & 0xFFL) << 56) | ((buf[start + 1] & 0xFFL) << 48)
            | ((buf[start + 2] & 0xFFL) << 40)
            | ((buf[start + 3] & 0xFFL) << 32)
            | ((buf[start + 4] & 0xFFL) << 24)
            | ((buf[start + 5] & 0xFFL) << 16)
            | ((buf[start + 6] & 0xFFL) << 8)
            | ((buf[start + 7] & 0xFFL) << 0);
}

public static long convertU16ToInt(byte[] buf, int index) {

    int firstByte  = (0x000000FF & ((int)buf[index]));
    int secondByte = (0x000000FF & ((int)buf[index+1]));
    int thirdByte  = (0x000000FF & ((int)buf[index+2]));
    int fourthByte = (0x000000FF & ((int)buf[index+3]));

    index = index+4;

    long anUnsignedInt  = ((long) (firstByte << 24
            | secondByte << 16
            | thirdByte << 8
            | fourthByte))
            & 0xFFFFFFFFL;

    return anUnsignedInt;
}

public static short toUnsigned(byte b) {
    return (short)(b & 0xff);
}


public static int convertU16ToInt(byte byte1, byte byte2) {
    int N = (( 255 - byte1 & 0xff )  << 8 ) | byte2 & 0xff;
    return N;
}

public static short UInt16Decode(byte inbyByteA, byte inbyByteB) {
    short n =  (short)(((inbyByteA & 0xFF) << 8) | (inbyByteB & 0xFF));
    return n;
}


public static long UInt32Decode(int inbyByteA, int inbyByteB) {
    int n = inbyByteA<< 16 | inbyByteB;

    return n;
}


public static long decodeMeasurement16(byte byte3, byte byte4) {
    return 0L;
}

public static double decodeMeasurement32(byte byte3, byte byte4, byte byte6, byte byte7) {

    double outdblFloatValue = 0;
    int outi16DecimalPointPosition = 0;

    int ui16Integer1 = convertU16ToInt (byte3, byte4);
    int ui16Integer2 = convertU16ToInt (byte6, byte7);

    int ui32Integer = ( (int)UInt32Decode (ui16Integer1, ui16Integer2) ) & 0x07FFFFFF;

    outi16DecimalPointPosition = ((0x000000FF - byte3 ) >> 3) - 15;

    // Decode raw value, with Exampledata: 0x05FFFFFC
    if ((100000000 + 0x2000000) > ui32Integer) {
        // Data is a valid value
        if (0x04000000 == (ui32Integer & 0x04000000)) {
            ui32Integer = (ui32Integer | 0xF8000000);
            // With Exampledata: 0xFDFFFFFC
        }
        ui32Integer = ui32Integer + 0x02000000; // with Exampledata: 0xFFFFFFFC
    }
    else {
        // Data contains error code, decode error code
        outdblFloatValue = (double)((ui32Integer - 0x02000000) - 16352.0);
        outi16DecimalPointPosition = 0;
        return -36; // Return value is error code
    }
    outdblFloatValue = (double)ui32Integer;
    outdblFloatValue = outdblFloatValue / (Math.pow(10.0f, (double)outi16DecimalPointPosition));

    return outdblFloatValue;
}

public static int toByte(int number) {
    int tmp = number & 0xff;
    return (tmp & 0x80) == 0 ? tmp : tmp - 256;
}

public static long getUnsignedInt(int x) {
    return x & 0x00000000ffffffffL;
}

}

After receiving the byte array, call Util.decodeMeasurement32 (byte [9], byte [10], byte [11], byte [12]). These bytes are temperature bytes.

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