Subject:
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(no subject)
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Newsgroups:
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lugnet.robotics.handyboard
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Date:
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Thu, 27 Jun 1996 00:26:44 GMT
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Original-From:
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System User <lylehaze@n-&NoMoreSpam&jcenter.com>
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Reply-To:
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Lyle Hazelwood <lylehaze@n-*saynotospam*jcenter.com>
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Viewed:
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1842 times
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Chuck McManis wrote:
> different power ranges whereas the software solution on the HC11
> gave me 8 to 16. I'll see about putting the source code up on my
I agree that the "software" solution in an HC11 is limiting. It is this
limitation that I am trying to overcome in hardware. Rather than shift
a bit-pattern out for PWM, I would use three of the built-in timers to
accomplish the task. One timer provides the period%100, the other
two would be the % of total desired for each of the two wheels. Please see
example 10-6 from the MC68HC11 reference manual, page 10-49.
While this would provide 100 power settings, I do NOT expect all of them
to be useful. Depending on the specific motors used and torque required,
many of the lower settings will not be sufficient to drive the motor. I
would just like to get a finer resolution to aid in matching the left and
right wheel speeds. Another advantage to the HC11 is that two additional
counters could be used to capture and count the encoder signals. (I have
geared my quad-encoders for 1/10" resolution).
I do not know squat about PIC's, except that I have read a bit, and believe
that they are capable devices.. I look forward to learning more. In that
vein, I have subscribed to Circuit Cellar INK, and wish they would start
mailing them.. still waiting... When I get my first issue, I will order
the back-issues you mentioned, and look forward to reading your articles.
The PWM solution I am currently working on is very similar to the HC11
method, except that it is done with discrete logic. While the details are
still a bit fuzzy, I am aiming for something like this.....
In the main interrupt loop of the HandyBoard(1 Khz), the desired speed of
each motor (0-100) is written out to an 8-Bit hardware counter. This
counter is decremented at a rate of 100 Khz by an on-board oscillator.
When the counter reaches 0, the borrow/carry line is used to disable the
clock into this counter, resulting in a stable off condition, until a new
value is written into the counter. Only the lower 7 bits are actually
latched into the counter. The upper bit is held in a separate latch (74hc74)
as a "reverse" bit. This should provide the PWM signals I am hoping for.
As an added bonus, it will shift the effective frequency of the PWM signal
upwards, hopefully to a less "audible" range.
I understand that this "design" is crude, and uses "old technology", but
it is also a clear indication of where my knowledge is now. As I get more
active in this new "hobby", I hope that my use of newer, more efficient
methods will become prevalent.
To do this with an HC11 would be a waste of resources. Once the timers are
set-up, the processor would be left almost completely idle! This is why I
would try to move lower-level navigation conrols to this co-processor. The
net result could be a LOGO-like interface to the wheels. Details regarding
acceleration, synchronization of the two wheels, de-accel at appropriate
times, encoder monitoring etc.. could be implemented within an HC11's
internal EEPROM/RAM, leaving the Master to more "intellectual" tasks.
Another advantage of using an HC11 would be the fact that I could use the
existing software tools for writing and downloading the assembler code.
Also, SPI to SPI between 68hc11's should not have compatibility problems.
I hope I have made this clear.. I am a novice in this field. I respect your
opinions, and will carefully consider any and all advice you may offer. I
would also like to ask you a few questions.. When you referred to your
"Home Page", did you mean a web page, or your directory in cher/pub?
Either way, I look forward to seeing the code. Also, If you have a chance
to nail down which month your article was printed in CircCellar, I look
forward to ordering (and reading) your work.
Thanks! Lyle Hazelwood (lylehaze@n-jcenter.com)
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