protocol.txt

The Beddit sensor shows as a normal Bluetooth RFCOMM (serial port)
device.

The sensor accepts a few newline-terminated ASCII commands. The ones I
know of are:

   OK -> sensor responds OK

   INFO -> sensor responds
     "INFO VERSION: 1.0; CHANNELS: normal, gained; SAMPLERATE: 140.0;
      SERIAL: xx:xx:xx:xx:xx:x; BUILD: 037d7f8"

   START -> sensor starts measuring and sending binary data.

The binary data comes in packets, the format of which is as follows:

dword packetNumber (consecutive)
word payloadLength
byte payload[payloadLength]
dword crc32

My sensor always sends 64 bytes of payload.

The payload consists of raw 16-bit samples. Words 0, 2, 4, ... are for
the "normal" channel, while words 1, 3, 5, ... are for the "gained"
channel. One 64-byte packet thus contains 2*16 samples, or 0.114
seconds worth of data at 140 Hz.

At least with my bluetooth connection data is occasionally lost, so
the receiving side needs to be able to detect dropped bytes and
resynchronize.

The CRC32 is calculated over the header + the payload.