iOS Swift Mi Scale 2 Bluetooth Get Weight

Question

I am writing an app that can get weight measurement from Xiaomi mi scale 2. After reading all available uuid's, only "181B" connection, specifically "2A9C" characteristic (Body weight measurement in bluetooth gatt) gets notifications.

Value data is [2, 164, 178, 7, 1, 1, 2, 58, 56, 253, 255, 240, 60]. Only last two values vary, the rest is time and date, witch is not set currently (253, 255 are zeroes when the weight varies on the scale until it stabilizes).

Can someone help me get only persons weight, should i be getting data maybe in a different way, from other uuid's (like custom ones: 00001530-0000-3512-2118-0009AF100700, 00001542-0000-3512-2118-0009AF100700), and how do i retrieve them.

Correct answer by Paulw11: You need to look at bit 0 of the first byte to determine if the weight is in imperial or SI; the bit is 0 so the data is SI. The to get the weight, convert the last two bytes to a 16 bit integer (60*256+240 = 15,600) and multiply by 0.005 = 78kg

Answer 1

I was using Mi Smart scale and i had the following byte array.

02-A4-B2-07-02-13-06-33-35-FD-FF-EC-09" received - 12.7 KG

02-A4-B2-07-02-13-06-3B-17-FD-FF-C8-3C" - 77.8 KG

I used the last two bytes to get the weights in KG.

(09*256 + EC)/200 = 12.7

(3C*256+C8)/200 = 77.8

My byte array was 13 bytes long.

bytes 0 and 1: control bytes
bytes 2 and 3: year
byte 4: month
byte 5: day
byte 6: hours
byte 7: minutes
byte 8: seconds
bytes 9 and 10: impedance
bytes 11 and 12: weight (divide by 100 for pounds and catty, divide by 200 for kilograms)

Answer 2

In my case, it was a little different:

I got data like this [207, 0, 0, 178, 2, 0, 0, 0, 0, 0, 127] (6.9 KG) and the solution is:

let bytesArray = [207, 0, 0, 178, 2, 0, 0, 0, 0, 0, 127]
let weight = (( bytesArray[4] * 256 + bytesArray[3] ) * 10.0) / 1000

And now I have my 6.9 kg.