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

Question

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 do I 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

Answer 1

It's not a beacon advertisement. The packets are the device sending three pieces of information.

• The device's local name "8BBAC49D"
• The Health Thermometer Service is available (with a current temperature measurement)
• The Battery Service is available (with a current battery level measurement)

Breakdown of this BLE discovered 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 

If you look at your repeat packet, you will see that each temperature measurement varies slightly, as does the battery measurement.

Here is the breakdown of the packet:

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

See the bluetooth 16-bit service UUID definitions for more information:

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