This is bluetooth (BLE) Gatt protocol for Lenovo HS11 Smart weight scale. It uses Chipsea CST34M97 chip, similar to some Huawei scales.
Main service = 0000fff0-0000-1000-8000-00805f9b34fb
Send command Characteristic = 0000fff1-0000-1000-8000-00805f9b34fb
Receive data Characteristic = 0000fff4-0000-1000-8000-00805f9b34fb
To read weight measurements, first you have to Write to Send command Characteristic and then read/handle Notify values on Receive data Characteristic.
Send command Characteristic
- Write
F2-00hex (or[242, 0]as byte array)
Receive data Characteristic
- Returns last N measurement records. Each measurement record is 10 bytes.
- Skip measurement records which start with
F2-00 - Last record is just 2 bytes
F2-00to indicate end. - Each measurement record consists of - Datetime of mesurement, Weight in kgs (upto 1 decimal), Impedance (to calculate BMI).
- Example measurement record -
67-1F-0F-1E-3B-F2-E0-7A-12-00
Measurement records -
// 67-1F-0F-1E-3B-F2-E0-7A-12-00
// First 5 bytes - measurement date time
// Next 2 bytes - scale type & weight
// Next 3 bytes - impedance
// byte0 = 67 (hex) = 103 (dec)
year
= ((byte0 & 240) >> 4) + 2017
= ((103 & 240) >> 4) + 2017
= 2023
month
= ((byte0 & 255) & 15) - 1
= ((103 & 255) & 15) - 1
= 6 // 0-based index, 6=July
// byte1 = 1F (hex) = 31 (dec)
day
= byte1
= 31 // 31st July, 2023
// byte2 = 0F (hex) = 15 (dec)
hour
= byte2
= 15 // 3pm
// byte3 = 1E (hex) = 30 (dec)
minute
= byte3
= 30 // 3:30PM
// byte4 = 3B (hex) = 59 (dec)
seconds
= byte4
= 59 // Time = 3:30:59 PM
// byte5 = F2 (hex) = 242 (dec)
scaleType
= byte5 & 240
= 242 & 240
= 240 // Always 240 for this scale
// byte6 = E0 (hex) = 224 (dec)
weight
= (((byte5 & 15) << 8) + byte6) * 0.1
= (((242 & 15) << 8) + 224) * 0.1
= 73.6 // kgs
// byte7-8-9 = 7A-12-00 (hex) = 122, 18, 0 (hex)
impedance
= byte7 + (byte8 << 8) + (byte9 << 16)
= 122 + (18 << 8) + (0 << 16)
= 4730Send command Characteristic
- Write
F2-01hex (or[242, 1]as byte array)