Sample code for serial (RS-232) connection between computer and Libela Elsi G 325 retail scale/weight

libela-elsi-g-325-weight.py

import serial

"""
Tehtnica: Libela Elsi G 325 (https://www.libela-elsi.si/en/retail-scales/retail-scales-without-printer/)
Protokol: TISA-4 (0)

https://pypi.org/project/pyserial/
https://pyserial.readthedocs.io/en/latest/shortintro.html

Podatki za povezavo s tehtnice: 9600 8 N 1
baudrate = 9600
bytesize = 8
partiy = N
stopbits = 1
"""

PORT = '/dev/cu.UC-232AC'

def checksum(bytes_string):
  """
  https://stackoverflow.com/questions/26517869/creating-xor-checksum-of-all-bytes-in-hex-string-in-python
  """
  cs = 0

  for el in bytes_string:
    cs ^= el

  return bytes([cs])

def fixed_5_bytes_price(price_as_string):
  price = round(float(price_as_string), 2)

  decimals = str(round(price % 1, 2))[2:4].encode()
  integers = str(int(price))[0:3].encode()

  return integers.rjust(3, b'0') + decimals.ljust(2, b'0')

def prepare_outgoing_data():
  start = b'98'

  price = input("Vpiši ceno izdelka (npr '4.2' za 4,2 €/kg): ")
  price = fixed_5_bytes_price(price) # '4.2' -> b'00420'

  cs = checksum(start + price)

  return start + price + cs + b'\x0D\x0A'

def display_incoming_data(in_data):
  data_str = in_data.decode()

  s = "Masa v mirovanju: {}".format("DA" if data_str[2] == "0" else "NE")
  w = "Izmerjena masa: {:.3f} kg".format(int(data_str[3:8]) / 1000)
  e = "Znesek OK: {}".format("DA" if data_str[8] == "0" else "NE")
  i = "Znesek: {:.2f} €".format(int(data_str[9:15]) / 100)

  print(s, w, e, i, sep = "\n")


# init
pos_to_weight = prepare_outgoing_data()
# print(pos_to_weight)

# open serial port
ser = serial.Serial(PORT, timeout = 1, write_timeout = 1)

# print data on the just created and opened serial device
# print(ser)

# send data
ser.write(pos_to_weight)

response = ser.read_until(b'\r\n')
#print(response)
display_incoming_data(response)

# close the connection
ser.close()