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

Chuck Green greencl at mindspring.com
Mon Jul 9 07:56:30 PDT 2007


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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