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

Jim Sanford wb4gcs at amsat.org
Mon Jul 9 18:30:37 PDT 2007


All:
I'm excited to read all of the emails on this topic.  Several thoughts, 
which I'd really like to discuss in more detail with all of you tomorrow 
night on TeamSpeak.
1.  As an experiment, and data collection exercise, I'd like to see the 
inductor Juan identified as the source of radiated EMI replaced with a 
shielded inductor or toroid.  As I mentioned to some of you, I saw a 
similar noise problem (source & victim were reversed) in my day job 
solved with exactly that one change.  I think this would tell us much 
about how big a problem we have (radiated and conducted), and be a 
useful piece of data for posterity.  As Bdale said almost two years ago, 
"Our legacy may very well be our documentation."

2.  Second, I'd like to see if we can, with a few ccomponent changes on 
the existing widget board change the switching power supply frequency as 
Juan suggested.  Another useful data point, with minimal effort.

Request for action:  Can one of Chuck, Lyle, Stephen, or Bdale take on 
obtaining a shielded/toroidal inductor of the same value and provide to 
Juan for testing, and then take on researching a change to the switching 
PS frequency?  IF so, Juan, would you and your team please make the 
changes and repeat testing?

3.  Regarding Chuck's comment:  If we wind up with Can-Do Too, I'd ask 
Juan if his accomplished project oscar team could take on component 
selection/purchase and construction of a couple of prototypes?  This 
could happen in parallel with John's redesign of the U-band receiver.  I 
know you guys have done a lot, but, YOU"RE GOOD!

4.  EMI Spec:  You put a gun to my head, and I'm going to pull out the 
MIL-STD, which is probably overkill, but MAYBE NOT.  I'd really prefer 
that one of you guiys current in the INDUSTRIAL world take on this task 
and come up with something good enough and reasonable.  In general, I'd 
like to eliminate as much mass and extra "touch" labor in the assembly 
process (multiple shields) as possible.  Bob Davis:  Please weigh in 
here, if the possible milled modules simplify this issue, please 
enlighten us.

5.  Chuck:  I appreciate your comments on lessons learned.  You 
obviously have some things in mind, please scribble them down, get them 
to me, and I'll get placed on the EaglePedia lessons learned page.

6.  CAN-Do! team:  Several folks have opined to me that it appears that 
the widget design is final, complete, and we'd better live with it.  I'd 
intended to discuss some of the above with you when Bdale got back.  I 
am EXTREMELY PLEASED AND GRATEFUL to see you stepping up to the plate 
and acknowledging the need and willingness to do something based on what 
Juan has learned.  Your intellectual honesty, integrity, and willingness 
to take on more for the team are recognized and appreciated. 

7.  Requirements:  Bob McGwier is correct, we really did start with a 
very top-level requirements document.  It is not perfect (Bob has hated 
it from the word go), but can be found on EaglePedia under Functional 
Requirements.  It is also in need of updating, after the October BoD 
decision.  On my list to do.  Like you, I have finite energy and time, 
but it is on my list.  I think John did an EXCELLENT job of documenting 
the UHF Receiver requirements based on what he knew.  The need for an 
EMI spec was not obvious, but is now, thanks to Juan's testing efforts 
and exceptional documentation.  Lou:  Functional requirements for power 
supplies?  Bob Davis:  Functional requirements for structure and thermal 
performance?  etc. etc.....we have much to do, but I think worthwhile 
effort.  By the way, I'm reading (in a few spare minutes here and there) 
an EXCELLENT book on requirements management.  When I finish, look for a 
review of it on my project management page.  I will also be providing 
suggestions on writing "good" requirements, based on that book and my 
recent experiences in the day job.

8.  Somebody brought up the issue of CAN bus vs. discrete wiring 
harness.  In my mind, the discrete harness is a non-starter.  WAY too 
much room for error and difficulty in testing.  Yeah, I know the AO-40 
harness was perfect the first time, but the guys who made that happen 
have made it clear to me that they don't ever want to do it again -- and 
I agree.  So, I think we should remain committed to the CAN bus for many 
reasons.  In my view, the recent "issues" with the CAN-Do! widget are 
just issues to deal with, not show stoppers.  The CAN-Do! team is 
willing to deal with the issues, and so should the rest of us.  Case 
closed in my mind.  As always, open to well-justified better idea, but I 
think the writing remains on the wall.

I'm sure there's more action following this recent discussion, but 
specifics currently elude me.  Feel free to send me suggestions, update 
the agenda for tomorrow night's TeamSpeak, and please be there.

Thank you all.
Very 73,
Jim
wb4gcs at amsat.org


Robert McGwier wrote:

>Bill Ress wrote:
>  
>
>>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
>>
>>
>>    
>>
>
>I also support the breadboarding of primary circuits.  And we did 
>develop our specifications for the latest incarnation of Eagle top down. 
>  We started with what services we wanted to deliver and moved down from 
>there.
>
>When I rejoined the project, and started the software defined 
>transponder movement, and long before I was leadership, the Can-Do was 
>"in the can".  I had almost no input to it. That said, I really do 
>support the goal of the CanDo.  Anyone who has heard of the horror 
>stories of Marie Marr and the wiring harness or seen Lou's spreadsheet 
>for interconnections  for AO-40 knows that these few words do not do it 
>justice.  We have found a gremlin.  That is normal in any project of 
>this complexity and is not easily remedied by specifications in a 
>project like this where the work and the tools necessary to make the 
>relevant measurements are spread over the globe.
>
>I look forward to our doing better as a team.
>
>Bob
>
>
>  
>
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