[eagle] Re: CAN-Do-Too! ??????????

Louis McFadin w5did at amsat.org
Mon Jul 9 20:32:45 PDT 2007


I agree with all your comments Chuck. I would add one additional and  
that is make some provisions for mounting the widget other than the  
connector.

Lou McFadin
W5DID
w5did at mac.com


On Jul 9, 2007, at 10:56 AM, Chuck Green wrote:

> Hi Guys,
>
> Juan has done a lot of outstanding work which resulted in some
> substantial critiquing of the CAN-Do!  (Affectionately called a
> "widget.")  It is unfortunate that it has taken several years since  
> the
> CAN-Do! was designed and then 100 units built before an application of
> sufficient sensitivity used it to discover it's shortcomings.  History
> can provide lessons that I hope we can learn from, but it seldom
> provides solutions to the problems encountered.  Lyle and I have
> exchanged a few thoughts privately and it seems it may now be time to
> consider solutions to the problems found.
>
> The only practical way to accomplish this is to develop the next
> generation CAN interface device.  Dare I call it the CAN-Do-Too!  ?
>
> All technical specifications should remain the same.  What this really
> means is that a next-generation controller must run *exactly* the same
> firmware currently running the CAN-Do! .
>
> All specifications added or redefined should be carefully defined  
> and be
> measurable.
>
> General specifications that we worked from before were that the widget
> should use as little power as possible and consume as little of a
> module's volume as possible.  The first of these should remain the  
> same,
> "use as little power as possible."
>
> But the second should be changed to "consume as little of the  
> connector
> panel space as possible" even if it means consuming a little more  
> of the
> module volume.  This means the widget PCB and components should not
> extend beyond the dimensions of the DA-15P connector in either
> dimension.  A possible compromise to this would be to let the PCB run
> past one end of the DA-15P but not more than the DA-15P is forced away
> from the side of the box by the box design.
>
> The power supply could be completely redesigned.  Or the inductor  
> of the
> existing supply could be exchanged for one that is a toroid (the
> existing one is not).  If someone wants to step up and design a new
> power supply, great!  If not, then we would simply change the  
> inductor.
> I'd sure like to see someone take this on.  With so many of these  
> in the
> satellite, only a few milliwatts is important.  And the noise issue  
> Juan
> uncovered is *very* important.
>
> It may be that some, or maybe all, of the widget should be enclosed  
> in a
> metal box.  It may be that just changing the inductor would allow a  
> new
> widget to meet the yet-to-be-defined noise specifications.
>
> The input power filter for module power should be separate from the
> widget power supply input filter.  The module power filter is a filter
> that will not meet all module requirements, but would likely meet the
> requirements of a digital module.  Some modules, such as receivers,  
> may
> need additional power conditioning.  But in any case, the widget power
> supply should not add to the module power supply noise.
>
> There should be a simple way to disconnect the filter capacitors on  
> the
> widget from the data lines when the widget is in Byte mode.  Most  
> people
> are not aware of this problem which was uncovered by another module
> builder.  It only effects those using the CAN-Do! in Byte mode.
>
> Using a synchronizing signal does not seem practical to us.  It would
> complicate the design of the widget power supply so that it would
> function with or without the presence of the synchronizing signal (we
> don't want to introduce a single-point-of-failure).  It would
> dramatically increase the satellite wiring harness complexity,  
> something
> the widget was intended to a simplify.  And it would inhibit the  
> widget
> power supply from going into various power-saving modes.
>
> Recruit some new people into this project.  Lyle simply doesn't  
> have any
> time for doing new designs right now.  We need a power supply designer
> as stated above.  And my time is limited.  I'm willing to lay out the
> new design and build a few prototypes, but I need others to do parts
> procurement and volume building of widgets.  I'll prepare flight units
> if desired.  We've talked about having someone skilled in parts
> procurement before but I don't know of anything having come of it.   
> The
> bottom line, if this is going to happen, Lyle and I need others to be
> involved.
>
> If you think this is a good idea, or bad, please express yourself.   
> And
> if you have other comments to add to the above, or would like to
> modify/expand on above comments, please do so.
>
> Looking forward to your comments,
>
> Chuck and Lyle
> _______________________________________________
> Via the Eagle mailing list courtesy of AMSAT-NA
> Eagle at amsat.org
> http://amsat.org/mailman/listinfo/eagle

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