Read voltage levels from BM2 Battery Monitor over BLE

BM2_read_voltage.py

#!/usr/bin/python3
import asyncio
import sys
from bleak import BleakClient

import binascii
from Crypto.Cipher import AES
from datetime import datetime

key = bytearray([(b&255) for b in [108,101,97,103,101,110,100,-1,-2,49,56,56,50,52,54,54]])

char = "0000fff4-0000-1000-8000-00805f9b34fb"

async def main(address, char):
   async with BleakClient(address, char) as client:
      print("[+] connected")
      await client.start_notify(char, callback_handler)
      await asyncio.sleep(100000.0)
      await client.stop_notify(char)

async def callback_handler(_, data):
   cipher = AES.new(key, AES.MODE_CBC, 16 * b'\0')
   ble_msg = cipher.decrypt(data)
   raw = binascii.hexlify(ble_msg).decode()

   voltage = int(raw[2:5],16) / 100.0
   power = int(raw[6:8],16)
   now = datetime.utcnow().strftime('%F %T.%f')[:-3]
   print("[%s] voltage: %.2f, power: %d" % (now, voltage, power))

if __name__ == "__main__":
   if len(sys.argv) != 2 :
      print("Usage: %s <mac address>\n" % sys.argv[0])
   else :
      address = sys.argv[1]
      asyncio.run(main(address, char))