qm1571-multimeter.py
====================

  Decode and write to stdout the output of the Fortune Semiconductor FS9721
  chip and the pin compatible Semico CS7721CN chip.  These chips form the
  heart of multimeters, some of which send the contents of their display
  as a binary stream over transmitted via wireless, USB or RS232.


Dependencies
------------

  - Either Python 2 or Python 3.
  - https://pypi.python.org/pypi/pyserial
    or Debian package python-serial.
  - Tested on Linux only with a DigiTech 1571 only.


Building, Installing and Running
--------------------------------

  There is no building required, and the only installation consists of
  download a copy of qm1571-multimeter.py to the current directory and
  making it executable.

  It accepts one optional argument on this command line: the name of
  the tty device the multimeter is connected to.  It defaults to
  /dev/ttyUSB0.

      ./qm1571-multimeter.py		# Display the data from /dev/ttyUSB0
      ./qm1571-multimeter.py /dev/ttyS1	# Display the data from /dev/ttyS1

  The multimeter sends the entire contents of the LCD display in
  every refresh. qm1571-multimeter.py prints the symbols
  displayed on the LCD on one line for each refresh sent, eg:

    +000.1 mV DC, AUTO 
    -000.3 mV DC, 
    -000.4 mV DC, REL 
    +0.L M ohm, AUTO
    
  Stop qm1571-multimeter.py by killing it (eg, by pressing ^C).

  If qm1571-multimeter.py gets data it does not understand it prints
  a line like the one below.  The hex is the data it could not
  decode.  Lines like the one below aren't much of a problem
  but their presence implies sometimes bad data will be slipping
  through unnoticed and so qm1571-multimeter.py will be displaying
  incorrect values.  This happens because the link layer error
  detection is very poor.

     ? 16.1d.f1.aa.fc.17.2f.3d.00.5d.67.7d.88.95.a0.b8.c0.d4.e8


License
-------

  Copyright (c) 2017,2021 Russell Stuart.

  This program is free software: you can redistribute it and/or modify it
  under the terms of the GNU Affero General Public License as published by
  the Free Software Foundation, either version 3 of the License, or (at your
  option) any later version.

  The copyright holders grant you an additional permission under Section 7
  of the GNU Affero General Public License, version 3, exempting you from
  the requirement in Section 6 of the GNU General Public License, version 3,
  to accompany Corresponding Source with Installation Information for the
  Program or any work based on the Program. You are still required to
  comply with all other Section 6 requirements to provide Corresponding
  Source.

  This program is distributed in the hope that it will be useful,
  but WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  GNU Affero General Public License for more details.


--
Russell Stuart
2017-Oct-10