Re: [Autopilot] PWM and Edge Counting Input

[Mark N. <m_l...@ya...>]

HI Tramm

>Tramm Hudson  wrote: 

>Mark Newell wrote:
>> I am new to the list but am trying to do basically
>> the same thing using a BasicX24 processor.

>Welcome! What sort of project are you working on?
.
.
.
.

My original idea was to build a "Roswell Flyer" clone.
I have been collecting parts for about a year. I felt
the resolution for PWM input and output would be ok. I
go alot for free samples and one can not always
dictate the packaging. I have thought about a 3 engine
flying platform, some how using thrust vectoring,
possibly including GPS. I have a lot of time, not too
much money, some neurological imparement from cancer
treatment, so I don't get things done too quick. I
look forward to following your progress and will
offer input if I can.

Thanks,
Mark

> Since it is somewhat limited I have tried> to off
load some of the processing. In particular i am using
a PAK-VII> from Al Williams to help with PWM input
processing and edge counting.> The chip has 8 channels
of input and the interface to a micro is easy.> There
is info at>
http://www.al-williams.com/awce/pak7.htmI'm a little
worried about its resolution for this
application.According to the web page, it has "16 bits
at 5uS resolution".If I'm reading that correctly and
it means 1 bit == 5 uS, thenits minimum acceleration
or servo pulse that it can sense isfairly long.For the
servos, the pulse is between 1000 us and 2000 us
wide.At the stated resolution, the PAK-VII would only
be able to resolve200 positions. That's less than 8
bits of precision and I knowthat is insufficient for
our application.The ADXL would have a similar problem.
You mention that you'reusing the 10 g version, which
will have 5 times less resolutionin the small
acceleration ranges. Depending on your
application,that may or may not be acceptable.> I have
the processor, gyros and Analog ADXL210 accelerometer.
I was> wondering if it might help with the noise
problems.We actually managed to eliminate most of the
noise from the systemthrough redesigning the mainloop
on the realtime board. You can seeplots of the
accelerometer samples as the source code evolved and
wetuned things to deal with the real-time tasks of
handling
thesampling:http://autopilot.sourceforge.net/accel.htmlHowever,
we're considering moving away from doing it with the
MCU.Brett has convinced me that using an FPGA for all
of the real-timetasks is the best way to offload the
CPU and let it get back tothe stabilization,
navigation and other more interesting tasks.> I have
not actually> tried it because I am some what "steady
challenged" ie slight tremmors> in my hands and have
not come up with an easy way to mount that little>
"blank" ADXL210 chip.I can't solder very well, either.
So I used the -EB version, whichis mounted on a small
PCB with five through-hole leads. You can seea picture
on the above page.Trammell-- -----|-----
hu...@sw... H 240-476-1373*>=====[]L\
Tra...@ce... W 240-453-3317' -'-`-
http://www.swcp.com/~hudson/
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