electronic_scale.cpp

#!/usr/bin/python
# vim: set expandtab:ts=2:sw=2

import argparse
import bluetooth
import struct
import sys

def checksum(msg):
  checksum = 0
  for c in msg:
    checksum ^= ord(c)
  return checksum

def format_request(args):
  msg = struct.pack('BBBBBB',
      1,                   # group
      args.gender == 'M',  # 0 = Female, 1 = Male
      1,                   # level. ???
      args.height,         # height, in cm
      args.age,            # age. in years
      1)                   # units. 1 = KG, 2 = LB, 4 = ST
  return '\xfe' + msg + struct.pack('B', checksum(msg))

def parse_reply(data):
  assert data[0] == 0xcf or len(data) < 16, 'Invalid reply'
  height = data[3]
  weight = (data[4] << 8 | data[5]) / 10.0
  return {
    'level': data[1] >> 4,
    'group': data[1] & 0xF,
    'gender': ["Female", "Male"][data[2] >> 7],
    'age': data[2] & 0x7F,
    'height': height,
    'weight': weight,
    'body_fat': (data[6] << 8 | data[7]) / 10.0,
    'bone': data[8] / 10.0,
    'muscle': (data[9] << 8 | data[10]) / 10.0,
    'visceral_fat': data[11],
    'body_water': (data[12] << 8 | data[13]) / 10.0,
    'base_metabolic_rate': (data[14] << 8 | data[15]),
    'body_mass_index': weight / (height / 100.0)**2
  }

def close():
  return '\xfd\x35\x00\x00\x00\x00\x00\x35'

def get_weight(args):
  uuid = '00001101-0000-1000-8000-00805F9B34FB'

  if not args.addr:
    print 'Scanning...'
    nearby_devices = bluetooth.discover_devices(duration=4,
                                                lookup_names=True)
    for addr, name in nearby_devices:
      if name == 'Electronic Scale':
        args.addr = addr
        print 'Found', args.addr
        break
  assert args.addr, 'Scale not found'

  service_matches = bluetooth.find_service(uuid=uuid,
                                           address=args.addr)
  assert len(service_matches) > 0, 'Scale service not found'
  service = service_matches[0]
  host = service['host']
  port = service['port']

  sock = bluetooth.BluetoothSocket(bluetooth.RFCOMM)
  sock.connect((host, port))
  sock.send(format_request(args))
  parsed_data = parse_reply(map(ord, sock.recv(1024)))
  try:
    sock.send(close())
    sock.close()
  except:
    pass
  return parsed_data

def main():
  parser = argparse.ArgumentParser(description='Bathroom scale')
  parser.add_argument('age', type=int, help='Age (in years)')
  parser.add_argument('gender', choices=['M', 'F'], help='Gender')
  parser.add_argument('height', type=int, help='Height (in cm)')
  parser.add_argument('--addr', help='Bluetooth address of the scale')

  args = parser.parse_args()

  for k,v in get_weight(args).iteritems():
    print k, v

if __name__ == '__main__':
  sys.exit(main())