could not read control point on BASIS 2 controller (MacOS, M1)

[alexrudd2]

Opened by ericshear26 at numat#171

Hi, I want to get four Alicat BASIS 2 MFCs to work with my Mac. They are definitely controllers, not meters. I am trying to establish serial connection between one MFC and the computer before I work on the others. The MFCs are connected to a BB8-DB9 breakout box with serial-DB9M cables. The breakout box is connected to the computer by an USB-USB cable. The breakout box is powered separately.

I know the FlowVision program exists for Windows, but the Python method should work on UNIX systems. I have gotten sensors and a stepper motor to work with microcontrollers on this Mac, so this shouldn't be any different.

Here is what I did:

• I pip-installed the alicat package (not sure if it's from the numat or alexrudd2 repository)
• I downloaded the Virtual COM Port driver for MacOS ARM and confirmed a successful installation.
• I confirmed that the computer "sees" the device. The address is /dev/cu.usbserial-DK0EUH0N.
• I downloaded PowerShell (now open source) and got it working in the terminal.
• I checked the baud rate of the serial connection. It keeps defaulting to 9600, because MacOS keeps closing the serial port and the baud rate resets every time. Using the exec 3<> command then the address in the terminal, I was able to hold the port open. When I then tried to change the baud rate to 38400, it returned 19200.
• When I ran it in terminal, I got the following error message:

(base) Eric@CHE-NAR-2G5L2C0 ~ % alicat /dev/cu.usbserial-DK0EUH0N
Traceback (most recent call last):
  File "/Library/Frameworks/Python.framework/Versions/3.13/bin/alicat", line 8, in <module>
    sys.exit(command_line())
             ~~~~~~~~~~~~^^
  File "/Library/Frameworks/Python.framework/Versions/3.13/lib/python3.13/site-packages/alicat/__init__.py", line 88, in command_line
    asyncio.run(get())
    ~~~~~~~~~~~^^^^^^^
  File "/Library/Frameworks/Python.framework/Versions/3.13/lib/python3.13/asyncio/runners.py", line 195, in run
    return runner.run(main)
           ~~~~~~~~~~^^^^^^
  File "/Library/Frameworks/Python.framework/Versions/3.13/lib/python3.13/asyncio/runners.py", line 118, in run
    return self._loop.run_until_complete(task)
           ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^
  File "/Library/Frameworks/Python.framework/Versions/3.13/lib/python3.13/asyncio/base_events.py", line 725, in run_until_complete
    return future.result()
           ~~~~~~~~~~~~~^^
  File "/Library/Frameworks/Python.framework/Versions/3.13/lib/python3.13/site-packages/alicat/__init__.py", line 71, in get
    state = await flow_controller.get()
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Library/Frameworks/Python.framework/Versions/3.13/lib/python3.13/site-packages/alicat/driver.py", line 365, in get
    state = await super().get()
            ^^^^^^^^^^^^^^^^^^^
  File "/Library/Frameworks/Python.framework/Versions/3.13/lib/python3.13/site-packages/alicat/driver.py", line 131, in get
    line = await self._write_and_read(command)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Library/Frameworks/Python.framework/Versions/3.13/lib/python3.13/site-packages/alicat/driver.py", line 345, in _write_and_read
    await self._init_task
  File "/Library/Frameworks/Python.framework/Versions/3.13/lib/python3.13/site-packages/alicat/driver.py", line 331, in _init_control_point
    self.control_point = await self._get_control_point()
                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Library/Frameworks/Python.framework/Versions/3.13/lib/python3.13/site-packages/alicat/driver.py", line 542, in _get_control_point
    raise OSError("Could not read control point.")
OSError: Could not read control point.

I ultimately want to run this in a Python IDE, but I'm not sure how to specify the baud rate with the asyncio package. My code looks like this so far:

import serial
import asyncio
from alicat import FlowController

port = '/dev/cu.usbserial-DK0EUH0N' # Connect to controller
baud_rate = 38400      # Baud must match controller's
ser = serial.Serial(port, baud_rate)

async def run_MFCs():
    async with FlowController(port, 'A') as MFC_airA:
        while True:
            readings = await MFC_airA.get()
            i = i+1
            print(i, readings)
            asyncio.sleep(0.5)

asyncio.run(run_MFCs())

Thanks for your help and I look forward to getting this to work.

[alexrudd2]

Sorry to hear you are having troubles, @ericshear26

Development has indeed moved here, and this is the version I publish to PyPI.

(Note: To quote multi-line paragraphs use triple-backticks ``` instead of single ones.)

It should not matter that you are on an M1 Mac. Although I'm on a Linux machine now, I did plenty of development on an M1.

Regarding your serial settings, you're close! However, it's not really necessary to set the baud at the OS level. Instead, each user / new connection of a serial port can set the baud while the port is in use. In fact, that's exactly what the driver does. FlowController accepts **kwargs and will therefore pass baud_rate down to SerialClient.

alicat/alicat/util.py

Line 150 in 9897771

def __init__(self, address: str, baudrate: int=19200, timeout: float=.15):

Try this modification to your code:

# import serial  ## unneeded, the driver will import it
import asyncio
from alicat import FlowController

port = '/dev/cu.usbserial-DK0EUH0N'
baud_rate = 38400
# ser = serial.Serial(port, baud_rate)  # unneeded; the controller will open the connection

async def run_MFCs():
    async with FlowController(address=port, unit='A', baudrate=baud_rate) as MFC_airA:  # notice keyword arguments!!
        while True:
            readings = await MFC_airA.get()
            i = i+1
            print(i, readings)
            asyncio.sleep(0.5)

asyncio.run(run_MFCs())```

[alexrudd2]

HOWEVER!!

The real problem here is that this driver does not currently support BASIS (i.e. thermal mass flow) devices. It's only been developed against the Laminar flow DP devices, such as the MC-series.

@avichalk had some working code for BASIS devices:

• Add support for Alicat BASIS devices numat/alicat#121
• https://github.com/avichalk/alicat/tree/basis

I'm still open to integrating that code. At the time, I did not because it made too many unrelated changes to the main codebase. A cleaned-up version is welcome :) Note I don't have a BASIS device, so any new code will have to come with tests.

[ericshear26]

Thanks, your suggested code worked after I added i = 0 outside of the while loop. It also works with Avichal's BASIS package (from alicat import basis) after I pip-installed it.

Now I'm trying to figure out how to change the unit ID of the other controllers. They seem to be identified as A by default. I'd need to change them to B through D to avoid conflicts.

[alexruddick-grantek]

Now I'm trying to figure out how to change the unit ID of the other controllers. They seem to be identified as A by default. I'd need to change them to B through D to avoid conflicts.

https://www.alicat.com/support/unit-id-baud-rate-tutorial/

[ericshear26]

Now I'm trying to figure out how to change the unit ID of the other controllers. They seem to be identified as A by default. I'd need to change them to B through D to avoid conflicts.

https://www.alicat.com/support/unit-id-baud-rate-tutorial/

That's for the Alicat controllers with a built-in screen. The BASIS controllers don't come with screens so I have to do it the Python way. I'm looking through the basis package for the right command to do this.

[alexrudd2]

Ah, in that case I'd try the command for Unit ID from the manual.

[ericshear26]

After trying to change the unit ids in Python, I finally broke down and used Alicat Serial Terminal on the Windows laptop to change the other controllers' IDs. It worked. I see all 4 controllers on FlowVision now.

I still want to use Python through the serial connection because I'd need to batch totalize each flow into my experimental system and this can be done precisely with Python. Is running async with the best way to handle each controller?

My code for two controllers, air and CO2, is as follows:

import asyncio
from alicat import basis

port = '/dev/cu.usbserial-DK0EUH0N'
baud_rate = 38400

async def run_MFCs():
    async with basis.FlowController(address=port, unit='A', baudrate=baud_rate) as MFC_airA: 
        i = 0
        while True:
            readings_airA = await MFC_airA.get()
            i = i+1
            print(i, readings_airA)
            # asyncio.sleep(0.5)

    async with basis.FlowController(address=port, unit='B', baudrate=baud_rate) as MFC_CO2:
        i = 0
        while True:
            readings_CO2 = await MFC_CO2.get()
            i = i+1
            print(i, readings_CO2)
            # asyncio.sleep(0.5)
            

asyncio.run(run_MFCs())

It returned the error message:

File "/Users/Eric/Desktop/Dissertation/Codes/Python/flowtest.py", line 25, in <module>
    asyncio.run(run_MFCs())
    ~~~~~~~~~~~^^^^^^^^^^^^
  File "/Library/Frameworks/Python.framework/Versions/3.13/lib/python3.13/site-packages/nest_asyncio.py", line 30, in run
    return loop.run_until_complete(task)
           ~~~~~~~~~~~~~~~~~~~~~~~^^^^^^
  File "/Library/Frameworks/Python.framework/Versions/3.13/lib/python3.13/site-packages/nest_asyncio.py", line 98, in run_until_complete
    return f.result()
           ~~~~~~~~^^
  File "/Library/Frameworks/Python.framework/Versions/3.13/lib/python3.13/asyncio/futures.py", line 199, in result
    raise self._exception.with_traceback(self._exception_tb)
  File "/Library/Frameworks/Python.framework/Versions/3.13/lib/python3.13/asyncio/tasks.py", line 304, in __step_run_and_handle_result
    result = coro.send(None)
  File "/Users/Eric/Desktop/Dissertation/Codes/Python/flowtest.py", line 8, in run_MFCs
    async with basis.FlowController(address=port, unit='A', baudrate=baud_rate) as MFC_airA:
               ~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Library/Frameworks/Python.framework/Versions/3.13/lib/python3.13/site-packages/alicat/basis.py", line 230, in __init__
    FlowMeter.__init__(self, address, unit, baudrate, **kwargs)
    ~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Library/Frameworks/Python.framework/Versions/3.13/lib/python3.13/site-packages/alicat/basis.py", line 52, in __init__
    loop.run_until_complete(tasks)
    ~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^
  File "/Library/Frameworks/Python.framework/Versions/3.13/lib/python3.13/site-packages/nest_asyncio.py", line 98, in run_until_complete
    return f.result()
           ~~~~~~~~^^
  File "/Library/Frameworks/Python.framework/Versions/3.13/lib/python3.13/asyncio/tasks.py", line 304, in __step_run_and_handle_result
    result = coro.send(None)
  File "/Library/Frameworks/Python.framework/Versions/3.13/lib/python3.13/site-packages/alicat/basis.py", line 48, in _is_basis
    self.control_point = await self._check_basis()
                         ^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Library/Frameworks/Python.framework/Versions/3.13/lib/python3.13/site-packages/alicat/basis.py", line 57, in _check_basis
    if check.split(" ")[-1][0] != 'B':
       ~~~~~~~~~~~~~~~~~~~~^^^
IndexError: string index out of range

[alexruddick-grantek]

You can use multiple expressions in a single async with context manager.

async with A() as a, B() as b:
    do_stuff(a, b)

Regarding that IndexError, It looks like a simple parse error. What is the value of check at that point? I would go through and compare the response to the manual.

[avichalk]

@ericshear26 glad to hear the BASIS package is working well for you!

The BASIS package (and, indeed, the Alicat library) only implement a small subset of possible commands, mostly commands that are useful for scripting. One-off administrative tasks like switching the unit ID are best handled through Serial Terminal or Flowvision.

It is possible to issue standard serial commands through the Python package, which can be used to change the unit ID, query the serial number, and so forth. You'll have to use a private module function, which isn't best practise or pretty.

import asyncio
from alicat import basis

async def get():
        current_unit_id = "A"
        new_unit_id = "B"

        async with basis.FlowController(address = "COM8", unit = current_unit_id) as flow_controller:
            print(await flow_controller._write_and_read(f"{current_unit_id}@={new_unit_id}")) ## or any other ASCII command
            await flow_controller.close()

asyncio.run(get())

By using this, you are bypassing the wrapper functionality of the library and issuing bare-bones serial commands. I wouldn't recommend using this in a script. It's best for one-off commands when you don't want to use Serial Terminal.