modbus-scale-client 1.1.3

Weigh scale Modbus Ethernet client

Table of Contents

[[TOC]]

1. Introduction

Modbus Scale Client provides the client-side capabilities required to communicate with the Mazzer and Rancilio weigh scales of project UC-02-2024 Coffee Cart Modifications.

2. Dependencies

Modbus Scale Client is part of the UC-02-2024 Coffee Cart Modifications software suite. Scale software has been split along hardware component lines, with the software for each hardware component residing in a separate GitLab repository.

1. modbus_scale_broker. The Arduino sketch that must be downloaded to the Uno.

2. modbus_scale_server. The Modbus Ethernet server daemon that runs on the Raspberry Pi.

3. modbus_scale_client. The Modbus Ethernet client that queries the server.

4. modbus_scale_ui. A Textual UI (User Interface) that displays the output of the Mazzer and Rancilio scales, and which can be used to tare (zero) either scale.

Because these repositories are designed to be deployed together as part of a comprehensive weigh scale solution, both hardware and software dependencies exist between them. These dependencies must be borne in mind when deciding whether or not to employ Modbus Scale Client in isolation.

Python packages are also available for the following software components.

• modbus_scale_server
• modbus_scale_client
• modbus_scale_ui

These packages may be installed using pip. Note however that the caveat regarding hardware and software dependencies still applies.

3. Installation

Two installation methods are available, with the most appropriate depending on whether the intent is to use the code base as-is, or to modify it.

3.1. PyPI Package

Those who wish to use the code base as-is should install the Python package via pip.

Whilst it is not strictly necessary to create a venv (virtual environment) in order to deploy the package, doing so provides a Python environment that is completely isolated from the system-wide Python install. The practical upshot of this is that the venv can be torn-down and recreated multiple times without issue.

$ python -m venv ~/venv

Next, activate the venv and install the package. Note that once activated, the name of the venv will be prepended to the terminal prompt.

$ source ~/venv/bin/activate
(venv) $ python -m pip install modbus-scale-client

3.2. GitLab Repository

Those who wish to modify the code base should clone the GitLab repository instead. Again, whilst not strictly necessary to create a venv in order to modify the code base, doing so is still recommended.

$ python -m venv ~/venv
$ source ~/venv/bin/activate
(venv) $ cd ~/venv
(venv) $ git clone https://gitlab.com/uc_mech_wing/robotics_control_lab/uc-02-2024/modbus_scale_client.git

Irrespective of whether or not a venv has been created, the requirements.txt file may be used to ensure that the correct module dependencies are installed.

(venv) $ cd ~/venv/modbus_scale_client
(venv) $ python -m pip install -r ./requirements.txt

4. Verification

In order to verify that Modbus Scale Client has been installed correctly, it is advisable to create a minimal working example.

$ touch ~/venv/example.py

If installed from the Python package, add the following.

import time

from modbus_scale_client import modbus_scale_client

client = modbus_scale_client.ModbusScaleClient(host = "<host>")

print("[INFO] Starting reading...")

while True:
    try:
        weight = client.read()
        weight = "{:8.1f}".format(weight)
        
        if client.server_exists() == True and \
            client.broker_exists() == True:
            
            print("[REAL] Scale weight = %sg" % weight)
        
        elif client.server_exists() == True and \
            client.broker_exists() == False:
            
            print("[ERROR] No broker detected")
        
        else:
            print("[FAKE] Scale weight = %sg" % weight)
        
        time.sleep(1)
    
    except (KeyboardInterrupt, SystemExit):
        print("[INFO] Stopping reading...")
        sys.exit()

If installed from the GitLab repository, replace the import statement with the following.

from modbus_scale_client.src.modbus_scale_client import modbus_scale_client

In either case, be sure to replace <host> with the IPv4 (Internet Protocol version 4) address of your physical Raspberry Pi. All going well, running the example code will produce output similar to the following.

(venv) $ python ~/venv/example.py
[INFO] Starting reading... 
[REAL] Scale weight =    123.4g
[REAL] Scale weight =    123.4g
[REAL] Scale weight =    123.4g
...
[REAL] Scale weight =    123.4g
[INFO] Stopping reading...

Note that verification assumes that all of the requisite hardware and software dependencies have been met.

5. Further Information

For further information about Coffee Cart Modifications please refer to the project UC-02-2024 group README.

6. Documentation

Code has been documented using Doxygen.

7. License

Modbus Scale Client is released under the GNU General Public License.

8. Authors

Code by Rodney Elliott, [e-mail]