Re: gEDA-user: hydraulic symbols and schematics

[Tom Hawkins <tomahawkins@xxxxxxxxx>]

On Wed, Apr 7, 2010 at 12:02 PM, Stuart Brorson <sdb@xxxxxxxxxx> wrote:
> Hi --
>
>> Obviously gschem is intended for electric circuits, but has anyone
>> used it for hydraulic schematics?  The hydraulics industry has defined
>> a fairly rich schematic language [1][2] for describing hydraulic and
>> pneumatic systems.
>>
>> I didn't find a gschem hydraulic symbol library, so I'm attempting to
>> build one.  My first stumbling block is the use of filled and
>> non-filled triangles, which differentiate hydraulic pumps from
>> pneumatic compressors.  Is it possible to draw filled triangles or
>> polygons with gschem?
>
> I don't think vanilla gschem currently supports filled regions.  But
> this is a frequently requested feature, and the folks in Cambridge may
> have coded up a solution based upon the whizzy graphic work they have
> done.

Well it appears to fill circles and boxes just fine.  Maybe it just
needs the ability to handle arbitrary polygons.

>
>> Do you foresee any other difficulties?  ... aside from simulating a
>> hydraulic circuit with spice or generating a layout.
>
> Actually, my first thought was:  What kinds of simulations (if any)
> does one do in hydraulics?  Are there any standard simulators?  If so,
> generating a netlist to feed to such a simulator might be an
> interesting hobby project.

We use Easy5 and Simulink.  But Easy5 doesn't run on Linux and both
tools are very clunky and neither have a standard format. This year I
plan to build some tools in this space.  It would be cool to netlist a
hydraulic design out of gschem and simulate it with other stuff like
embedded software and vehicle dynamics.

If you look at some hydraulic schematics, you'll see a rich duality
between electric and hydraulic circuits.  For example, the pressure
drop across an orifice is analogous to the voltage drop across a
resistor.  Hydraulic power is pressure * flow (i.e. V * I).

>
>> (BTW at Eaton, we have a history of bending EDA tools for our
>> purposes.  We used GTKWave to view and analyze vehicle data in
>> realtime.)
>
> Awesome!  How did you get the real time info into GTKWave?  IIRC, it
> only reads .vsd (and other simulation) files.

We extract vehicle data via. a CAN bus.  We then convert the streaming
CSV data into VCD and pipe this into GTKWave.  The command line reads:

$ readCAN | tovcd - | shmidcat | gtkwave -v -I my.sav

We put a laptop in the passenger seat when we take our test vehicles
out for a drive.  With the analog features of GTKWave, you can see all
the vehicle data varying in realtime.  It's really cool.


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