I've been quiet as most things I might have added have already been stated. Regarding the power from the spacecraft, think automotive power standards (really ugly). The power will likely come from switching sources (at least some of the time) and is not shielded so subject to everything else running around in the wiring harness and stray stuff from transmitting antennas, etc. There is some filtering of this in the CAN-Do! so each application will have to decide if any added filtering is needed.
Robert McGwier wrote:
Not to mention that ALL power supplies to the oscillators were specified to have adequate filtering and noise immunity. We need to revisit that. There is NO power supply coming from the spacecraft bus where you may assume it is nice, flat, and quiet. Assume it is ugly, raw, and must be conditioned.
Bdale Garbee wrote:
On Sun, 2007-06-10 at 20:04 -0700, Juan Rivera wrote:
To my surprise the module jumps briefly to about 57 kHz at regular intervals of about 3 seconds.
Yes, that's the watchdog timer firing and causing a software reset. I have no doubt that the reset cycle causes a short-term variation in the current consumption profile on the board itself. If the frequency is power consumption dependent, note that it's likely to move around a bit during normal operation... might want at some point to look at conditions with the CAN-Do! running at a "normal" 20ms update rate.
My next plan is to probe all 40 pins by using a 10x scope probe. I’ll start another log called CAN-Do Noise and start posting there as I start on this task.
As Lyle pointed out in an off-list email, the power supply on the CAN-Do! widget was designed to be efficient, not necessarily to be quiet. Switchers always have noise issues... we've flown a lot of them, and this isn't the first time some filtering or shielding has been required to keep everything happy. You're doing the right things to characterize what's going on, and we'll all help if/as needed.
We (the CAN-Do folk) are following your progress with great interest. Augmenting the CAN-Do! documentation with some summary of your findings and mitigation approach to aid future users is something we'll look forward to doing.