[eagle] Re: CAN-Do Suggestions from Juan
wb4gcs at amsat.org
Tue Jul 17 20:15:13 PDT 2007
Some comments on this thread, as I indicated earlier.
In no particular order:
" . . working in a vacuum." To not do so is why we have EaglePedia, and
why I have been pushing for requirements and sharing of lessons
learned. The harsh reality is that Juan and his team have been testing
some of our stuff in new ways, and we're learning things. Perhaps we
could/should have learned some of these things in the past, I don't
know. We didn't, but we know them now, so let's press ahead.
Regarding the board flexing issue: Juan, please add this to your
lessons learned. It would be a welcome addition to the component
selection talk that Lyle gave at Pittsburgh. In the mean time, please
extract all the things that you've learned we should do differently into
a text document that I can add to the lessons learned sub page from my
project management page. I'll get Dave to post, this is all good stuff.
Milled enclosure: Bob Davis is looking into that. I've asked Dick
Jansson to locate an unmodified sheet metal enclosure to get into Juan's
hands for evaluation. Many considerations here, let's make decisions
based on EVALUATION.
EMI: We need requirements, but nobody has stepped up to write or
extract. My threat (grin) to dig out the MIL-SPEC was properly
incinerated. So, we still have no requirements. I offer the following
"top level" EMI requirements, based on my earlier post regarding the 3
things it takes to have EMI:
1. Every potential EMI source (like switching power supplies)
should be as quiet and well shielded as reasonably posible.
2. Every potential EMI victim should be as immune to conducted and
radiated (other than on-channel thru the antenna) as reasonably possible
I'll leave it to guys like Tom Clark to tell me what exponent we should
attach to the value of this in the aggregate of many sources and
victims, I just know that attention to the basics on a per module basis
will make our lives much easier at integration/testing time.
We also need to standardize on IF output levels from RX modules and
input levels from SDX to TX modules. Volunteers?
I think the above provides all the guidance we need to proceed with an
electrical redesign of the U RX based on what we've learned so far.
We'll need Bob's input on housing studies and we'll need to assess what
the CAN-Do! team is up to before committing to PCboard layout and
construction. Juan thinks we should wait until some top-level specs are
better refined; we'll come through this discussion.
Regarding the CAN-Do widgets: The team has offered to do a redesign.
I'm reluctant to get too carried away on this. We've learned some
things that we'd like to change regarding the power supply, but the rest
of it works, and we should not toss that. So, this is an area where I
very strongly feel that incremental improvement is in order, not a
wholesale redesign. My sense is that the power supply noise issues
we've discovered IN TESTING were not anticipated by design folks who are
not necessarily power supply experts. (Bdale just confirmed this on the
phone.) Now that we have them, we're seeking such experts. We may get
some input soon from someone who is such an expert who knows somebody
who knows somebody who is on the team. If any of the rest of you have
such expertise or know somebody who has it, please step up to the
plate. I'm gratified at the willingness of the CAN-Do! team to do
whatever it takes, but DO NOT want to toss the baby with the bath water
-- we then start over, and cannot afford that in time, intellectual
effort, or $$ Part of this discussion is the recent conversation
regarding high density connectors. If we need them and they're
acceptable, so be it. Some seem to think this is a big deal, I do not
-- it's a technical issue to be evaluated and dealt with.
One commentor expressed disappointment about silence regarding these
changes and lack of direction from "management". I have been following
this conversation closely, but have not weighed in since I had no new
thoughts or extraordinary value to add. Rest assured, I follow these
issues closely, and try not to weigh in unless I have something
significant to say. My silence to this point should be interpreted as
satisfaction with the conversation and apparent direction. If ever you
think I should weigh in and am not, ask the explicit question.
Chuck asked if someone would pursue alternative inductor components to
reduce radiated noise. I have asked Juan to see of Project Oscar would
take this on. I think there is tremendous value in testing with
substitues of this single component.
It is CRITICALLY important that we demonstrate something this year. We
need it to dispel doubts and we need it to encourage fund-raising. Our
hosts, the Wireless Association fo the South Hills (WASH) have committed
to helping us do this. They will provide a 30+ foot tower on a trailer,
antennas, coax, and I'll provide a power supply. We have a working
U-band RX, and may have a better one. Bob McGwier assures me that we'll
have a working SDX to demonstrate. I'll get a 2m TX for it to drive at
significant power. This will allow us to demonstrate Eagle in the hotel
and in the surrounding area -- vital for publicity and fundraising. We
also need to show IHU and CAN-Do!, ifthey're working and sending
telemetry on the "downlink", so much the better!
We have much to do in a few short months. Let's get on with it.
Thanks & 73,
wb4gcs at amsat.org
Juan Rivera wrote:
> Forgive this long email...
> SInce everything is interrelated the only way to deal with it is from
> a system engineering perspective (in my opinion). You can't design
> the various subsystems with each group working in a vacuum. If you
> do, this is what happens.
> For example: I've researched the maximum amount of bending that
> should be allowed on a SMT circuit board. AVX, the capacitor
> manufacturer, suggests a maximum bend radius spec for SMT circuit
> boards of 60 inches. That works out to 0.0084" maximum deflection
> over any 1" segment. That's about the thickness of three sheets of
> paper. The tolerances of the existing sheet metal enclosure with
> separate heat sinks and multiple swaged-on stand-offs is way too
> loose, by at least an order of magnitude. The enclosure I have is
> also warped and flexes. To me that means we need a milled enclosure...
> If we're going to do that we might as well do it right and make it
> into two separate cells with noisy digital circuits in the front and
> analog in the back...
> If we do that then you probably don't have to worry too much about
> radiated emissions or changing the PCB form factor or connector...
> Filtering conducted EMI would rise to the top of the list of
> concerns. Moving the switching frequecies of all the supplies up as
> high as possible would ease the filtering burden on everything on the
> satellite and tend to push any spurs out of the passband. And so
> forth and so on...
> Once we had some hard data on the amount and characteristics of the
> conducted EMI from the power distribution point, then John could start
> designing in the necessary EMI filtering and CPB layout to fit into
> the box and meet the yet to be determined EMI susceptability
> requirement for the receiver. If his design didn't look like it would
> be able to meet the requiement then there would be some push-back to
> the power distrubution subsystem to clean up their radiated EMI, etc.
> I guess the bottom line would be that since you can't know the
> radiated and conducted EMI susceptability of everything that may end
> up connected to the CAN-Do module, all you can do is try to make it as
> clean as you can and get the switching frequency as high as possible.
> By the way, I just looked up the Maxim converter you're using and it
> looks like it's very lightly loaded which would explain wny its
> running at 5 kHz instead of the 200 kHz they spec. I spent some time
> looking for a better choice and couldn't find anything, but I don't
> know what you requirements are.
> On 7/17/07, *Chuck Green* <greencl at mindspring.com
> <mailto:greencl at mindspring.com>> wrote:
> Hi Juan,
> I agree that specifications prior to design would be helpful
> (required?). But as far as the EMI issues are concerned, we do
> seem to
> have a chicken/egg problem. And I'm not sure it is practical to
> a widget that meets the requirements of receiver modules. Most
> simply don't need anything nearly this good. But we should do
> everything practical to accommodate receiver modules, and maybe meet
> their requirements completely.
> Juan Rivera wrote:
> > Chuck,
> > My comments might have been buried in the flurry of email a
> while back.
> > Things seem a bit quieter now so here they are:
> > 1) Don't get too far into a redesign until a top-level EMI
> requirement is
> > created. This can't be done properly until prototype solar
> panel power
> > converters are fabricated and tested. I would work to create a
> new power
> > supply with a switching frequency of at least 500 kHz while you wait
> > however. This will make filtering much easier, the filter
> components will
> > be smaller, and any spurs that make it into the receiver will be
> outside the
> > passband of the IF.
> > 2) The EMI requirements for radiated and conducted emissions and
> > susceptibility should flow out of that test data and not be
> > 3) Once we have an EMI requirement then tradeoffs need to be
> > between the CAN-Do module and the enclosure - one or two
> compartment? Sheet
> > metal or milled construction? The results of that tradeoff
> study will
> > determine how much room you have to work with, how much front
> panel space,
> > and how much shielding and filtering are required.
> > If I had my way the enclosure would be a two-cell milled
> enclosure with all
> > the RF and IF exiting out the side of the rear cell. The CAN-Do
> module and
> > the Receiver switching power supply would both be located in the
> first cell
> > with feed-thru filtering in the common bulkhead between cells
> (all digital
> > power in the front and all analog in the rear). That would mean
> that the
> > CAN-Do connector would be the only connector on the front of the
> case. If
> > that were true then the only reason to change connectors would
> be to save
> > weight or increase reliability. It would also mean that the
> existing CAN-Do
> > PCB footprint would be fine as it is.
> > In my presentation I will suggest that the next revision of the
> 70 cm
> > receiver should be postponed until all of these issues are resolved.
> > 73,
> > Juan
> > -----Original Message-----
> > From: eagle-bounces at amsat.org <mailto:eagle-bounces at amsat.org>
> [mailto:eagle-bounces at amsat.org <mailto:eagle-bounces at amsat.org>]
> On Behalf Of
> > Chuck Green
> > Sent: Monday, July 16, 2007 7:47 PM
> > To: Louis McFadin
> > Cc: Dave Black ((Work)); Dave Black ((Home)); David Smith; AMSAT
> > Samsonoff at Mac. Com; Juan.Rivera ((Work))
> > Subject: [eagle] Re: CAN-Do-Too! ??????????
> > Thanks, Lou.
> > I don't know of any reason not to use them either. Obviously,
> it needs
> > to meet our mounting configuration requirement so the new mechanical
> > design can meet the objectives I stated earlier. This means it must
> > mount on the edge of a PCB. I think the HD15-D has three rows
> of pins
> > so I'm not sure how this can work, but I haven't looked at the
> > parts available so maybe this problem has been solved.
> > If we are going to seriously consider using HD connectors I
> think we
> > need the blessing of AMSAT's VP of Engineering and the EAGLE project
> > coordinator. This would be true for any change that would be
> > in the satellite.
> > I am a little disappointed that there have not been any comments
> > regarding the changes I saw as being made with a new design.
> > Additions/changes/questions/etc. I don't think we should do a new
> > design without this discussion. Maybe people feel these issues
> > been well covered in the past. If so, a simple "looks good to
> me" would
> > be helpful.
> > And no one has stepped up to say they are well qualified and
> will design
> > a new power supply. Without this, I don't see a new design
> > but maybe.
> > And finally, I see that no one has dared touch the subject of parts
> > procurement I raised.
> > Obviously, most of these comments are really meant for the Cc list.
> > Thanks,
> > Chuck
> > Louis McFadin wrote:
> >> Chuck,
> >> Mouser has a very large selection of D-sub connectors including the
> >> high density versions. Most are in stock.
> >> I see no inherent reason for not using them.
> >> Lou McFadin
> >> W5DID
> >> w5did at mac.com <mailto:w5did at mac.com> <mailto:w5did at mac.com
> <mailto:w5did at mac.com>>
> >> On Jul 16, 2007, at 7:19 PM, Chuck Green wrote:
> >>> I have had one experience with the high density D
> connectors. They
> >>> were much larger pin count than 9 or 15! After someone
> >>> insisted that we use them I did the board lay out. Turned out
> >>> they were *totally* unavailable!!! I did the board layout
> >>> again@#$%&^* using standard Sub-D's. That was a number of
> years ago
> >>> so I would hope things have changed. If someone is absolutely
> >>> confident they can obtain the parts we need then I'm not at all
> >>> opposed to using them (remember, I'm not volunteering to do parts
> >>> procurement for this project; this is a good time to use someone
> >>> that's good at parts procurement).
> >>> While at Goddard for P3D vib test I noticed NASA satellites using
> >>> standard Sub-D's. That was also a few years ago. Anyone know of
> >>> High Density Sub-D's being used on other satellites?
> >>> Chuck
> >>> Bdale Garbee wrote:
> >>>> On Tue, 2007-07-10 at 09:02 -0700, Chuck Green wrote:
> >>>>> The sub-miniature D connector series has served us well. If
> >>>>> has *experience* with something they think might be a better
> >>>>> choice, we'd love to hear about it.
> >>>> At the AMSAT annual meeting that was held near Washington,
> D.C., a
> >>>> couple of years ago (three?), someone approached me after the
> >>>> talk that Stephen and I gave to ask why we weren't using the
> >>>> higher-density connectors that put 15 pins in the same shell
> size as the
> >>>> 9-pin version of the series we have been using... and
> followed up by
> >>>> sending me what looked like mil/aero-spec samples of such a
> part that I
> >>>> probably still have in my basement somewhere. I'm sorry that
> I can't
> >>>> recall at all who that person was, but it was someone who
> claimed to be
> >>>> using such connectors professionally with good results.
> >>>> At the time, we weren't likely to be redesigning the units
> any time
> >>>> soon, so I didn't take any action on this suggestion. If
> we're going to
> >>>> revisit the design and think we need more than 9 pins, it
> might be worth
> >>>> investigating higher density connectors like that?
> >>>> Bdale
> > _______________________________________________
> > Via the Eagle mailing list courtesy of AMSAT-NA
> > Eagle at amsat.org <mailto:Eagle at amsat.org>
> > http://amsat.org/mailman/listinfo/eagle
>Via the Eagle mailing list courtesy of AMSAT-NA
>Eagle at amsat.org
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