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  • Author Author: Jan Cumps
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Sound and Vibration Measurement: Instrument Network Service for LabVIEW Pt1: Software Components

Jan Cumps
Sound and Vibration Measurement: Instrument Network Service for LabVIEW Pt1: Software Components

For the Sound and Vibration Measurement Hat for Raspberry Pi road test, I'm reviewing Measurement Computing's IEPE Measurement DAQ HAT for Raspberry Pi.
The next series of posts are going to be a subplot. I'll make software to remotely control the DAQ, via LabVIEW.
In the first post, I'm laying out the software components. 

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I'm not 100% new to this. I wrote a SCPI service for a Pi before, a two channel Lab Switch:  SCPI on a Linux Board. That design is simpler, but there's a significant part of infrastructure and groundwork that I can reuse.

Software Components

There will be 3 modules.

  • an instrument service in c++, on the Pi, that uses low level commands  to control the DAQ over TCP/IP. Can be used in its raw form.
  • a SCPI service in c, also running on the Pi, that allows to talk SCPI to the instrument. It 'll be a bridge between LabVIEW and the instrument service.
  • a LabVIEW instrument driver that knows how to automate the DAQ. Runs on the test PC and sends the commands to the Pi over TCP/IP. 

Then, there 'll be some support work:

  • service wrappers and setup instructions, so that the instrument runs as daemon and is available upon boot.
  • example LabVIEW flows as training material
  • a real showcase with the vibration test gizmo I'm making for this road test.

Borrowed components:

For most of this, I know how to do it. One aspect that I'm not familiar with, is how to stream big data results to a LabVIEW client. I will try to learn and implement that, but no promises.

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image: preview snippet from the custom LabVIEW driver for this instrument: the comms initialisation.

Repository

The code is available, in a very premature form, on my github. I'll keep updating it as I go. You can take a peek.
Currently, there are two subfolders for the Pi service projects. I don't know yet if I'll use github for the LabVIEW driver.
Because this is an extensive task, I will not take feature requests :). I'll take help and advice (and contributions) though.

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Preview (April 7, 22)

Minimal functionality works for both services. The system knows how to enable the auxiliary power supplies and query their status: 

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image: active debug session, with the DAQ:IEPe#? and DAQ:IEPe# commands working

Link to all posts.

  • Fast (x8) and silent preview of the video that shows current status:

    I'll do the talk-over in the coming week.

  • If you are familiar with the National Instruments / LabVIEW Virtual Instruments paradigm: I'm trying to stay as close as possible to that.
    I've been doing that for all SCPI compatible instruments I made on element14. It allows that the average skilled LabVIEW designer can use it.

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    All blocks that control or poll the instrument have a familiar representation. And there is a tree view that lists the available blocks. You could see this as a one page API overview.

    I've used it to build flows with Tektronic, Keithley and Rigol instruments. Scopes and power supplies.
    When I designed the e14 DC Load I used the same approach. Similar for the driver I made for the MultiComp PRO waveform generator.
    I haven't seen a better form of abstraction for instrument control yet. An abstraction that doesn't block you from any lower level.

  • in reply to Jan Cumps

    (and if you just need to start the application without debug - you can double click the entry.  It's the same as selecting Run. This will also build, upload and execute the binary, but it will not stop in the debugger and wait for you)

  • A little trick for efficient start of a debug session:

    In Eclipse, you can show all Launch Configurations in a window, via Window -> Show View. This allows you fast access to start your particular config.
    If you right-click it and select debug, it 'll build the binary, deploy it on the target and start it with remote GDB Server.
    This saves a few memory and dialog navigations and immediately gets you in a debug session.

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  • First instrument query completed: Get sensitivity of a channel.

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    In action: 

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