Hi Bart,

> ... I don't see
> the extra pair of wires as a huge drawback, and this would
> allow devices to choose what they needed.  In particular,
> this would let the microcontroller run off USB power, which
> means that groups like PARTS could reuse our layout and PCB
> for the microcontroller half-board as-is.

It turns out it is a big deal to "just add" 5V power to the boards.

1. We'll need a new connector for our power distribution and USB system, 
which is harder than you'd think. The current connector we have turns 
out to have great properties, including very small size and robustness. 
We could make the connector bigger, I suppose. We could add a spare 
connector off to one side, I suppose.

2. We'll need more circuitry onboard, like a linear regulator or another 
switching supply since our boards run at 3.3V.

3. We have to worry about grounds, and how the two supplies interact, 
and what happens when the 5V supply goes down, and other complications 
like that. It's not a stunningly hard problem, nor is it trivial.

I know that we keep going over this because it's just such a nice idea 
that other groups can use our boards. We're trying to build something 
that goes to space; I just think there are parts of that constraint that 
don't fit with other applications. There are LOTS of close fits, but 
none exact.

Now, as I mentioned before, there are some parts of our circuits that 
CAN be completely reused. As we move towards using kicad, I look forward 
to putting each "module" - LPC2148, sensors, actuators, etc - that can 
be in it's own schematic/layout file, so that at least our sensor 
designs can be directly reused by other groups. But I think our LPC2148 
front end is just not one of those.

Andrew

-- 
-------------------------------------------------------
Andrew Greenberg

Portland State Aerospace Society (http://psas.pdx.edu/)
[EMAIL PROTECTED]  P: 503.788.1343  C: 503.708.7711
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