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

Bill Ress bill at hsmicrowave.com
Mon Jul 9 10:29:08 PDT 2007


All - -

To add support to Juan's conviction that we need to start developing 
"top down" specifications versus the bottom up activities we've been 
involved with, I would add that  in order to develop a  "realistic" EMI 
spec for the satellites power distribution system, we really need to 
know what those circuits will do.

With that in mind, I feel we need to breadboard the key circuits 
associated with that system and get hard data versus shooting from the 
hip with assumptions. At some point this power system is needed anyway, 
so why not focus design attention on that "top level" system now and get 
that issue settled - or at least better understood?

On the issue of housing panel area, and the possible consideration of a 
Mark 2 version, I think if I remember correctly, there were comments on 
wondering why a DB-9 (or even a physically smaller connector series) 
couldn't be used or are all the 15 pins needed?

Regards...Bill - N6GHz

Juan Rivera wrote:
> Chuck and Lyle,
>
> I'm in the process of writing up my presentation for the next AMSAT
> symposium so all of these issues have been on my mind constantly as I write.
>
>
> I believe that any modification of the CAN-Do module should flow out of a
> comprehensive review of the top-level satellite requirements.  There needs
> to be an EMI specification that covers radiated and conducted emissions and
> susceptibility for Eagle. Any need for changes to the CAN-Do module should
> flow directly from that EMI spec.  An analysis of the requirements might
> show a need to break the module enclosure into two sections.  If the module
> enclosure was changed to a two-section configuration, with all of the
> digital electronics in the front and the analog in the rear, then the RF
> would need to enter and exit out the side.  If that were the case, I believe
> that the existing CAN-Do PCB size would be OK as currently configured.  And
> of course, all of the above would directly impact the next revision of the
> receiver since it would determine the physical layout of the PCB as well as
> the size and configuration of any EMI filtering that was needed.
>
> An analysis of the Eagle EMI requirements might also show that a move to a
> much higher switching frequency would be advised since it would ease the
> burden on filters and move any artifacts outside the passband of most analog
> payloads.
>
> Bottom line - I would hold off making any hard decisions until a
> comprehensive EMI requirement for Eagle is created and analyzed.
>
> 73, Juan
>
>
>
> If designing a new power supply is determined to be necessary then I would
> strongly suggest a move to as high a switching frequency as is practical.
> This will make filtering much easier.
>
> -----Original Message-----
> From: Chuck Green [mailto:greencl at mindspring.com] 
> Sent: Monday, July 09, 2007 7:57 AM
> To: juan-rivera at sbcglobal.net
> Cc: eagle at amsat.org; Bill Ress; Dave Black (Home); Dave Black (Work); Dave
> hartzell; David Smith; Don Ferguson; Juan.Rivera (Work); Samsonoff at Mac. Com
> Subject: 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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