New Python project using a BeagleBone Black

Question

I'm looking for directions/guidance for the best direction to take with this new project. I have a VNA that is controllable via Python/Pi-Visa and a network cable. I also constructed a custom relay switching board so that I can test up to 32 connection points(using 16 relays) without reconnecting my VNA. The attached image is the 8Ch version I made. My question is if anyone has had experience with instrument control via Python and/or the BB Black, what direction should I take? Thanks 
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shabaz · Accepted Answer

Hi Jon,

Is your Python program (that uses pyvisa) also running on the BBB, or on a different machine?

If your board has one logic level input per relay then some general-purpose I/O library can be used to control it.

If you wish to use Python, there is a BBB GPIO library that may help, I've not tried it but hopefully it should work.

There is a GPIO API example here.

The above assumes that your pyvisa based code runs on the same BBB that has the relay board connected. If you want to make your code general-purpose so it can work remotely too, then some client-server code can be used.

There is a project by Jan Cumps that you can use for that, called SCPI on a Linux Board. The code you write to control the I/O would be included at the instrument side of that project, and then it gets controlled in a similar way to your VNA.

jomoenginer · Answer

Derek Molloy has some good examples of how to interface the GPIOs of the BB Black. Some of the example may be dated but they should still point you in the right direction. His source code that can be downloaded has some Python examples that might be of interest to you. http://exploringbeaglebone.com/chapter8/ The Adafruit examples that were referenced previously are another good source of examples. What relay driver does the board use? It is possible that you may find examples already created for the driver it uses. For a Python GUI, you could use wxPython or tkinter which would run directly on the BBB. Or you could use something like Flask and Javascript and Python to publish a browser based application for remote control of the Relay board. Then there is the whole NodeRed thing.

Jan Cumps · Answer

My code i not hard to adapt to another relay board - even your home-grown - or a BBB. There's a limited piece of code that talks to the hardware. Where-ever you see a SPI call, replace it by the code to control your relays. Except for the SPI part, nothing is RPi or BBB specific. It's plain linux APIs.

shabaz · Answer

Hi Jon,

I think all of this can be achieved easily. First step would be to wire up the relay board to the BBB (using the GPIO API link earlier to see which pins are allowed - not all GPIO pins on the BBB are directly usable), and then use the examples there to prove that they can be switched on/off with the Python GPIO API. Next, take Jan's SCPI project, and include the GPIO API and swap in the GPIO commands in place of SPI that the code currently uses (or let us know if you need help with that, once you know the GPIO pin numbers mapping).

Now your relay board will be controllable just like the VNA. Then is straightforward to write code to wait for an input or cycle through connections.

jomoenginer · Answer

Some instruments also have a serial interface and even a RESTful interface (although this does require a network connection) all of which can be controlled from Python. Some of new devices from Keysight require a Windows COM object to remotely control the instrument making it a bit interesting to using a non Windows system for connection. What interface does your Relay board use?

shabaz · Answer

Hi Jan, I figured your code would be flexible enough : ) It sounds like a perfect fit for Jon's requirements, with just a short exercise mapping from his relay board to the GPIO pin numbers, and inserting in the GPIO API above in place of SPI.

New Python project using a BeagleBone Black

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