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Discussions pertaining to the electrical issues (e.g. circuitry, power, etc.) of Pumpkin's CubeSat kit.


Postby bgat » Tue Nov 28, 2000 6:58 am

The USB setup should allow access to everything inside the Cubesat from one connector. Whatever that means--- I don't even use the USB port on my PC!

Could USB also be used as a communications backplane, between boards in the box, a'la a small local-area network? Being able to tap onto that network from outside would be very cool.

I worked on a design like that once, only it used '485 as the media. We found no end of uses for the setup, from "sniffing" around to see what was going on, to loosely-coupled multiprocessor setups where the control algorithm was distributed across processing modules.


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Re: USB?

Postby aek » Tue Nov 28, 2000 9:57 am

I think the main problem / impediment w/regard to USB is that implementing USB is non-trivial, and it's unlikely that any one USB implementation would make everyone happy.

For example, USB has two different speeds, there are a wide variety of USB interface chips available, all with their supporters and detractors, and USB is a bit much for the the PIC16F877 if you plan on doing anything else with it.

I am leaning towards a slightly different USB "attitude": namely, we provide the mechanical means to accept a USB connector, and we leave it up to the kit user to implement USB.

The overall topology of our CubeSat kit suggests that a small (e.g. 1" x 2") daughterboard with a USB connector, passive components, a connector and perhaps even a USB controller could be mounted in the same plane as the main PCB. Then, that USB PCB connects to the user PCB. Depending on how the CubeSat user goes from there, USB could power the entire unit, allow sniffing in both the user electronics and the PIC, etc.

We could also make it so that the same area could implement a simple DB-9 for a serial connection to the PIC on the main PCB instead. That would be much easier to develop and integrate, but has the disadvantage that you can't / shouldn't bring power into the CubeSat over a serial DB-9.

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