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<DIV><FONT face=Arial size=2>I really should stop calling it an altimeter...
it's really just a timer at this point. By moving down to the Basic Stamp I
rather than the II, I've sacrificed the memory necessary for datalogging, and
hence, altitude assessment.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Anyway, I've managed to come up with a modified
circuit to take care of what I need:</FONT></DIV>
<DIV><FONT face=Arial size=2><A
href="http://www.me.mtu.edu/~bjsikkem/mycircuit.jpg">http://www.me.mtu.edu/~bjsikkem/mycircuit.jpg</A></FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Rather than using a Basic Stamp II board - a board
containing everything, interpreter, memory, etc - I've moved down to the Basic
Stamp I chipset, and simply integrated the PARTS into my design. This saved me
some decent dough - the Basic Stamp I costs $34, whereas with my setup the total
cost at this point is $33.something. It also saved me some parts. I realized
looking at this guys design that he has a regulated 5v line for the
accelerometer, which just happens to be exactly what the BS1 needs. The BS1
board comes with a voltage regulator on it, but that becomes unneccesary if you
have a regulated 5v line already. I also removed the reset circuit, saving
myself some more parts and weight.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>The only thing not shown on my schematic at this
point is the relay that will trip the ejection charge. That will connect to
pin12 on the PBASIC1/P.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>As I've said, I can't do any datalogging with this
setup. The BS2 that this guy had contained 2048bytes of memory, some of which is
used for program storage, and the rest held only 12 seconds of data. The BS1
contains only 248bytes of EPROM, again, some of which is used for the program
itself. So no room for any useful storage (and no way to upgrade the memory, as
the BS1 interpreter assumes 248bytes of memory!)</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>What I can do, though, is write up a little program
to take a look at the acceleration data coming from the accelerometer, and time
an ejection charge (or even a staging charge) with this. Here's how it would
work:</FONT></DIV>
<DIV><FONT face=Arial size=2><A
href="http://www.me.mtu.edu/~bjsikkem/data.jpg">http://www.me.mtu.edu/~bjsikkem/data.jpg</A></FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>That graph contains some real flight data from the
orginal altimeter, as well as what I suspect the data would have looked like
beyond the point where his parachute ejection took place, had it not. As you can
see, the phases of flight are easily discernable, and it should be fairly
straightforward to discern when they change, during flight. At the beginning you
have powered flight, where the rocket is accelerating very quickly in the
positive direction (acceleration is in the direction of the rocket nose). Then
the engine cuts off, and you have a fast negative acceleration (in the oposite
direction of the nose) as gravity and drag pull back on the rocket. As drag
slowly decreases, the acceleration approaches -9.8m/s. That's all shown in the
actual data. Now for the theory (solid theory, though!). As the rocket passes
apogee, the nose begins to point down. The acceleration is still obviously
9.8m/s due to gravity, but now the rocket is accelerating in the same
direction as the nose is pointing again. Which means it would be positive
acceleration again, at 9.8m/s. </FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>So, all I would need to do is look for the second
time the acceleration passes through 0, and time an ejection charge accordingly.
</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Any comments? It all seems like it'll work to me,
but I could be missing something here...</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Incidently, Analog Devices is about the coolest
company ever. I ordered some samples from them yesterday - a couple
accelerometers, and an AD converter. I got them TODAY!!! Yeah, that's right,
they sent my measily little 3 ICs UPS Next Day Air. For free. I have no idea
why. I ordered a sample from National Semiconductor, and they told me 3-15 days,
which seems much more reasonable to me. But hey, whatever floats their boat!
:)</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Oh, and I'm also pissed because the local Radio
Shack closed doors this summer. Yeah yeah, I know, crappy store, maybe, but now
I have to order even the simplest electronic bits - which is not cool when I'm
working on a project! All I needed was a proto board, now I've gotta wait a week
for it to get here... bleh.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Brian</FONT></DIV>
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