[eagle] Re: CAN-Do noise abatement plan and questions

Chuck Green greencl at mindspring.com
Wed Jun 13 07:24:13 PDT 2007


Hi Juan,

I'll take a cut at some of your questions and let Stephen correct me.

Juan Rivera wrote:
>
> Good morning Stephen,
>
> I do have a few questions. Thanks for asking!
>
> 1) What if the CAN-Do module suffers a failure that causes a current 
> overload? Is it protected by a fuse? The next generation receiver 
> should continue to function as long as it has power. An overload in 
> either unit should not cause the other to fail.
>
The CAN-Do! does have a 2 amp fuse at it's power input. The switched 
current to the module also goes through this fuse. If the module mission 
requires it to be impervious to the condition of this fuse, then 
additional power input to the box is needed. If this power requirement 
is small (less than a couple of amps) then you could use one or more of 
the "user" pins on the CAN-Do! If the power requirements are large (such 
as a transmitter) then an external connector should be used and that 
power controlled by the CAN-Do! supplied "switched" power. In either 
case, the module design should measure the current and provide that as 
telemetry (more on telemetry below).
>
> 2) Do you have any information of previous efforts to reduce CAN-Do 
> noise by either shielding the module or replacing the inductor with a 
> shielded version?
>
I think you are the first.
>
> 3) Do you have a shielded inductor that I could swap for the existing 
> one if that proved necessary?
>
None has been looked for.
>
> 4) Have you designed a circuit that would allow temperature to be 
> determined inside the receiver PCB itself, and not just on the CAN-Do 
> module? This will be important, especially if the receiver is split 
> into two separate enclosures.
>
There are some "user" analog inputs to the CAN-Do! that can be used for 
this or any other analog thing you want included in the telemetry.
>
> My plan is to desolder the CAN-Do module from the receiver PCB today 
> and move the receiver PCB to the enclosure’s rear set of mounts. This 
> will put about 2-inches of space between the two. I’ll make up two 
> interconnecting cables – one just long enough to attach the two while 
> in the case, and one that is a foot or two long, assuming that I can 
> find the parts I need and don’t have to solder the cable to the two 
> units. I can use that long cable to try some troubleshooting. I’ll use 
> that CAN-Do’s noisy inductor as the noise source and move it around 
> over the receiver to see what affect it has. Perhaps I can find the 
> area that is the most susceptible to noise that way.
>
> I think the next receiver could use the entire available board space to:
>
> 1) Put distance between the two modules
>
> 2) Further isolate the CAN-Do module with a shield if necessary
>
> 3) Add power supply input filtering and input current overload protection
>
> 4) Include CAN-Do data line filtering if that turns out to be necessary
>
> 5) Add a temperature sensor in the vicinity of the SAW filters, and 
> another on the second PCB if it gets split into two sections
>
> One last question… How do I reduce the heartbeat timing below three 
> seconds? I couldn’t find any way to do that using the net controller. 
> I’d like to confirm that the jump in frequency I see in the CAN-Do 
> module’s 5 kHz noise every three seconds goes away.
>
I think your question is "How do I stop the CAN-Do! from having its 
watchdog time out?" You can't change the length of the watchdog timeout 
as that is set by the firmware in the CAN-Do! Sending the CAN-Do! 
config. packets at intervals of less that three seconds should stop the 
CAN-Do! from resetting. It is intended that the IHU will do this in the 
satellite at 20 ms intervals while collecting telemetry.

I hope this helps,
Chuck
>
> 73,
>
> Juan
>
> ------------------------------------------------------------------------
>
> *From:* smmoraco at gmail.com [mailto:smmoraco at gmail.com] *On Behalf Of 
> *Stephen Moraco
> *Sent:* Tuesday, June 12, 2007 7:21 PM
> *To:* Juan Rivera; Juan Rivera
> *Cc:* Jim Sanford; Bdale Garbee
> *Subject:* late to tonight's meeting
>
> Juan,
>
> Sorry I missed your presentation/discussion tonight.
>
> Any questions/issues for me re: CAN Do! ?
>
> Regards,
> Stephen
> --
>
> kc0ftq at amsat.org <mailto:kc0ftq at amsat.org>
>
> ------------------------------------------------------------------------
>
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