Intro

Some experiments to read Medisana "BS 430" data to own data store: automatically reads weight and all features (kCal, fat, ...) to a InfluxDB database. It currenlty runs on a RespberryPI Zero W.

Installation

This requires:

• Go: https://golang.org/doc/install
• GATT: go get github.com/andreaaizza/gatt
• InfluxDB client: go get github.com/influxdata/influxdb1-client/v2
• A InfluxDB server with a writable database (set host, db, user and pass to config.json)
• A Medisana "BS 430" (might work on some other Medisana models, but could not test it). Get the Bluetooth MAC address (you can use your mobile phone and Bluetooth scan, while the Bluetooth logo is blinking on your Medisana "BS 430", i.e. after a weight measurement on a recognized profile -- see manual), and set the config.json appropriately

To build and install:

git clone github.com/andreaaizza/bs430
cd bs430
make 

Run it once, customize generated config.json.template to config.json and run it.

How to read data from Medisana "BS 430"

Bluetooth service

Service: 0x78b2, includes measurements and commands Characteristics:

• 0x8a21 -> indication, weight
• 0x8a22 -> indication, features (kCal, ...)
• 0x8a82 -> indication, customer (including profile number, ...)

Procedure

1. Subscribe to all indications SetIndicateValue()
2. Write current Epoch (2010) on 0x8a81 WriteCharacteristic(..., []byte{0x02}, epoch2010()...)
3. Read and decode indications Read indications and decode values (see INSTRUCTIONS)

Instructions

See also: https://github.com/oliexdev/openScale/wiki/Medisana-BS444

From characteristic 0x8a21:

byte 0: unknown
byte 1-2: weight in little endian / 100
byte 3-4: unknown
byte 5-8: unix date/time stamp in little endian starting from year 2010
byte 9-18: unknown
Second package is send from UUID 0x8a22 as follow:

From characteristic 0x8a22:

byte 0: unknown
byte 1-4: unix date/time stamp in little endian starting from year 2010
byte 5: unknown
byte 6-7: kCal in little endian
byte 8-9: fat percentage in little endian / 10 and first byte is masked with 0xF0
byte 10-11: water percentage in little endian / 10 and first byte is masked with 0xF0
byte 12-13: muscle percentage in little endian / 10 and first byte is masked with 0xF0
byte 14-15: bone mass in little endian / 10 and first byte is masked with 0xF0
byte 16-18: reserved bytes

From characteristic 0x8a82:

byte 0: unknown
byte 1: profile number (uint8)

Sample weight decode

2019-07-15T21:38:39.114Z INFO Attribute value changed, handle: 0x1B, value (0x): 1D-7A-17-00-FE-44-B7-EF-11-A0-17-00-FF-03-09-00-00-00-00

7A-17 -> echo 'ibase=16;obase=A;177A/64' | bc = 60.10

Epoch 2010:

Epoch (2010) is the count of seconds from Jan 1 2010, little endian coded.

How to read it: 44-B7-EF-11

date +%s -d 2010-01-01
1262300400
echo 'obase=16;1262300400' | bc 
4B3D2CF0
echo 'ibase=16;obase=A;11EFB744+4B3D2CF0' | bc | date -d @$( cat - ) 
Mon 15 Jul 2019 10:38:12 PM CEST

How to get current:

echo "obase=16;$(( $( date +%s ) - 1262300400 ))" | bc