Brymen BM257s Serial Library

Small Python 3 library to access the serial interface of Brymen BM257s multimeters. It is developed with the Brymen BRUA-20X USB kit and uses the Brymen 6000-count digital multimeter communication protocol, so it should work with other BM25x models as well.

The library reads the serial stream sent by the meter in a dedicated thread, so that you can query the current value at any time without any special effort on your part.

Installation

The easiest way to install this library is to use pip within a virtualenv:

$ git clone [email protected]:RobertWilbrandt/bm257s.git && cd bm257s  # Clone library
$ pip3 install -r requirements.txt  # Install requirements
$ pip3 install .  # Install library

Basic Usage

Example 1: For a very quick test of connectivity, you can bring up a text console showing the current reading from the meter:

brymen-console /dev/USBPORT

If you're not getting any data, remember to hold down the HOLD button on the meter while turning it on.

Example 2: To print a line every time the meter transmits an update (roughtly every 200 ms):

with BM257sSerialInterface(port) as interface:  # open the port and start the reader thread
	while True:
		interface.wait()  # block until there's data
		measurement = interface.read()
		print(str(measurement))

Example 3: To print the 2-second average reading and standard deviation at 10-second intervals:

interface = BM257sSerialInterface(port, window=2)  # open the port
interface.start()  # start the reader thread
interface.wait()  # wait for meter to start transmitting
time.sleep(2)
while True:
	measurements = interface.read_all()
	if measurements:
		average = bm257s.measurement.average(measurements)
		stdev = statistics.stdev(average.values)
		print(f"{str(average)} SD={stdev}")
	time.sleep(10)

Output

The read() function returns a Measurement subclass, representing the most recent measurement, with the following typical properties:

• type: The physical property being measured: "Voltage", "Temperature", etc.
• unit: The base units for that property: V, Vrms, Ω, etc. For temperature, "C" and "F" indicate which scale is being used by the meter.
• value: The floating-point value in those units
• display_unit: The range of units being measured, as shown on the meter display: mV, kΩ, etc.
• display_value: The floating-point value in those units, as shown on the meter display

The read_all() function returns a list of Measurement objects representing the most recent measurements received from the meter within the configured window.

These measurements can be individually processed or automatically combined using the measurement.average() function. The resulting single Measurement includes an additional values property containing the list of all non-null values used to compute the average value.

For more detail, use the help() function in Python.

Limitations

The library currently supports only a single Brymen protocol. See TODO.md.

Contributing

This project uses various linters to enforce its code style:

• The black code formatter
• isort for nicely sorted imports
• The flake8 linter
• The pylint linter

They are integrated into automatic testing and run automatically in CI.

Testing

This project uses tox for testing automation. It runs the included unittest tests and checks the linters discussed in Code Style.

If you want to run the tests locally you first need to install tox using pip3 install tox. Then you should be able to start testing:

$ tox