PWM and Rabbit

Would anyone be able to give me a headstart on implementing pulse width
modulation with a Rabbitcore 3600?

If someone could explain or provide me with a link, I would appreciate
it. I understand the idea of PWM but working with microcontrollers is
new to me. I searched the 3600's user manual and it more or less listed
that it had the capabilities to do PWM, but did not describe how to use
it. I may even be looking in the wrong place for this information but a
quick google search was unsuccessful. Thanks!

Brian

Traffibm@gmail.com wrote:
> Would anyone be able to give me a headstart on implementing pulse width
> modulation with a Rabbitcore 3600?

I can't help with the specifics, but I can provide you with more
information to help you dig.

PWM is also known as "output compare" mode. Look for information about
using the timers. It's usually buried in the datasheet somewhere around
there.

The way you do PWM on a micro in general:

1) Setup the timer
2) Set the timer in "output compare" mode
3) Set the value at which the output changes stage (0 to 1 or 1 to 0)
When the timer overflows, the output will be set to one value. When it
hits the "compare" value it will change stages.

So if you have the "compare" value close to zero (if counting up) then
you get very little signal, if it's close to the end of the timer
period, you get a bigger signal, etc.

ttyl,

--buddy

> Brian

On 12 Feb 2006 16:11:34 -0800, Traffibm@gmail.com wrote:

>Would anyone be able to give me a headstart on implementing pulse width
>modulation with a Rabbitcore 3600?
>
>If someone could explain or provide me with a link, I would appreciate
>it. I understand the idea of PWM but working with microcontrollers is
>new to me. I searched the 3600's user manual and it more or less listed
>that it had the capabilities to do PWM, but did not describe how to use
>it. I may even be looking in the wrong place for this information but a
>quick google search was unsuccessful. Thanks!
>
>Brian

Brian,

There is a quite active yahoo e-mail list centering around the
rabbits. I'm sure you get help there. Then they also host a lot of
application notes on their website and I would be very surprised if no
PWM sample would be among them.

Markus

Thanks for the tips and suggestions. I will check out yahoo and dig
into all the datasheets, which I have to obtain from a project
teammate.

Just to give some background information on our project, we are in the
process of designing a semi-autonomous blimp using a
microcontroller(Rabbitcore 3600 Module), an Inertial Navigation System
with gyros and accelerometers, sonar sensors, and powerful brushless DC
motors. The largest challenge to overcome is weight since helium is
lighter than air, but with a 6 foot blimp we can lift about 12 ounces
with helium alone. Batteries, even Li-Pos are somewhat heavy in this
reference.

Thanks again for the PWM info as it should help us interface these
motors to the Rabbit.

Brian

In article <1139882025.081987.237960@f14g2000cwb.googlegroups.com>, 
Traffibm@gmail.com says...
> Thanks for the tips and suggestions. I will check out yahoo and dig
> into all the datasheets, which I have to obtain from a project
> teammate.
> 
> Just to give some background information on our project, we are in the
> process of designing a semi-autonomous blimp using a
> microcontroller(Rabbitcore 3600 Module), an Inertial Navigation System
> with gyros and accelerometers, sonar sensors, and powerful brushless DC
> motors. The largest challenge to overcome is weight since helium is
> lighter than air, but with a 6 foot blimp we can lift about 12 ounces
> with helium alone. Batteries, even Li-Pos are somewhat heavy in this
> reference.

I hate (or love---who knows) to point out the obvious, but powerful
motors and big batteries do sort of go hand-in-hand!

Sonar sensor also require significant peak power---it sounds more like
you have a sensor---battery---motor  power problem than a processor
power problem.   There are lots of options that you can pic (pun 
intended) from it you have 30 to 50mA for the processor.

Still, LIPOS are probably a better choice than NIMH for the unit----
just build the charging smarts into an external package.


> 
> Thanks again for the PWM info as it should help us interface these
> motors to the Rabbit.

You have an advantage in that PWM for motors can have pretty slow
overall periods----if you don't mind a bit of acoustic whine from
the system.  Those motors act like bit inductive filters.  If you
do your PWM properly,  you can even use the inductance to limit
current and use a higher-than-rated voltage--as long as you never
let the PWM go to DC!  (That usually means faster PWM rates, though).


Sounds like a fun project.  Now if you can get enough lift 
capacity,  perhaps you could do a version of  a cable-free
skycam for NBA games!  (you heard it here first!)

Mark Borgerson

Mark Borgerson wrote:
> Traffibm@gmail.com says...
>
... snip about autonomous blimp ...
> 
> Sounds like a fun project.  Now if you can get enough lift
> capacity,  perhaps you could do a version of  a cable-free
> skycam for NBA games!  (you heard it here first!)

I can see it now.  Barrage balloons around the Super Bowl, with
model Spads firing tracer rounds to eliminate the invading blimps.

-- 
"If you want to post a followup via groups.google.com, don't use
 the broken "Reply" link at the bottom of the article.  Click on 
 "show options" at the top of the article, then click on the 
 "Reply" at the bottom of the article headers." - Keith Thompson
More details at: <http://cfaj.freeshell.org/google/>
Also see <http://www.safalra.com/special/googlegroupsreply/>

In article <43F162AC.3BA5435E@yahoo.com>, cbfalconer@yahoo.com says...
> Mark Borgerson wrote:
> > Traffibm@gmail.com says...
> >
> ... snip about autonomous blimp ...
> > 
> > Sounds like a fun project.  Now if you can get enough lift
> > capacity,  perhaps you could do a version of  a cable-free
> > skycam for NBA games!  (you heard it here first!)
> 
> I can see it now.  Barrage balloons around the Super Bowl, with
> model Spads firing tracer rounds to eliminate the invading blimps.
> 
> 
In that case, let's fill them with hydrogen and make things
really intereting.   Hmmm,  I wonder if I need to borrow
my brother-in-law's firefighter turnouts and helmet for my
next football game?   ;-)


They use the cabled skycams for NFL games---but blimps would
probably work for the covered stadiums.

You can tell I spent way too much time today on PWM drivers 
and servo motor power tests!   ;-(


Mark Borgerson