Data Sheet
ID. It also allows for packet capture by a PC for analysis of performance.
IMPLEMENTED (v2.1)
Version History
1
Experimental and Proof of concept. Used to refine the Packet Capture code,
develop flash storage of the Transmitter ID, and general operation of the wixel as
a bridge device. Text only protocol and commands.
2
Consumer ready version. All packets are retransmitted as binary packets.
Implemented:
Wixel Power Mode 2 sleeping
Wixel not sleeping on USB connected to PC.
Battery monitoring
HM-10 module power down
Protocol Functional Level 1
Protocol
Each packet of data sent or received by the bridge is described below. Common to each
packet are the first two 8bit bytes. The first byte is the length of the packet in bytes. The
second is an ID for the type of packet being sent.
Note that packets sent from the bridge to a phone app will include a last byte representing
the Protocol Functional Level that the wixel firmware is programmed to. This was requested
by Stephen Black, and makes sense. If more protocol functionality is added in future, any
app using the bridge will need to know how to deal with various versions of firmware/protocol
level in the wixel.
Data Packet
A Data packet is sent by the wixel to the phone app. It contains the relevant data sent from
the Dexcom G4 Transmitter, plus the bridge battery voltage and TxID it is filtering on.
The data packet has the following structure:
Byte
Value
Data Type
Description
0
0x11
8 bit unsigned integer
Number of bytes in the
packet (17)
1
0x00
8 bit unsigned integer
Code for Data Packet
2:5
Raw Signal
32 bit unsigned integer
Raw Sensor signal
6:9
Filtered Signal
Filtered Sensor signal
10
Dexcom Tx Battery Voltage
8 bit unsigned integer
The Transmitter battery
voltage. Usually around
214 for a new
transmitter. The app
should alert if this
reaches <= 207, that the
transmitter requires
replacement.
11
Bridge Battery Percentage
8 bit unsigned integer
The bridge battery
percentage (0-100). This
is calculated from the
VIN voltage using a
10k/2k7 resistive voltage