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

John B. Stephensen kd6ozh at comcast.net
Mon Jul 9 11:13:32 PDT 2007


Yes, we need a specification for the DC power bus before approval of the 
requirements for the next U-band receiver. I've got the DC voltage in there, 
but there needs to be a specification for conducted EMI.

73,

John
KD6OZH

----- Original Message ----- 
From: "Bill Ress" <bill at hsmicrowave.com>
To: <juan-rivera at sbcglobal.net>
Cc: <eagle at amsat.org>; "Juan.Rivera (Work)" <Juan.Rivera at gd-ais.com>
Sent: Monday, July 09, 2007 17:29 UTC
Subject: [eagle] Re: CAN-Do-Too! ??????????


> 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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