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

John B. Stephensen kd6ozh at comcast.net
Mon Jul 9 10:33:56 PDT 2007

This will be a very useful project, especially if it can be done in parallel 
with the next revision of the U-band receiver. A shielded (either torroidal 
or pot core) inductor will go a long way in reducing EMI as will changing 
the configuration of the filtering. There will still be a radiated electric 
field so a sheilding box should be designed at the same as the new PCB. It's 
useful to keep input and output connectors at opposite ends of the connector 
mounting bracket, so the new widget should be as narrow as possible. The 
shield should sit above the module PCB, if possible.



----- Original Message ----- 
From: "Chuck Green" <greencl at mindspring.com>
To: <juan-rivera at sbcglobal.net>
Cc: "David Smith" <w6te at msn.com>; "Dave Black (Work)" 
<dblack at mail.arc.nasa.gov>; "Dave Black (Home)" <dblack1054 at yahoo.com>; 
<eagle at amsat.org>; "Samsonoff at Mac. Com" <samsonoff at mac.com>; "Juan.Rivera 
(Work)" <Juan.Rivera at gd-ais.com>
Sent: Monday, July 09, 2007 14:56 UTC
Subject: [eagle] CAN-Do-Too! ??????????

> 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
> _______________________________________________
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