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Subject: 
Re: Why do it? Was: multi-device output controller
Newsgroups: 
lugnet.robotics, lugnet.robotics.rcx.pbforth
Date: 
Fri, 26 Mar 1999 23:05:02 GMT
Viewed: 
10 times
  
Ralph, Thanks for reigning in the rabbit chase!

As the originator of this thread I'd like to respond to the 'why'...

I keep running out of ports on my creations.  I see 5 or 6 as a practical limit.  My criteria for a
solution:

1.  Entirely compliant with RCX firmware.
2.  Clean programmability.  My initial idea: control is accomplished by setting the power level of a
port to select which device, and by setting the second port for actual device performance (on/off,
fwd/rev, pwr level).  This means it would be usable by the RIS software.
3.  Reasonable cost (In my mind this means < $50).
4.  Leave at least 1 port for normal, direct RCX control.

The directions this thread has taken are not attaining this goal.  Instead of blue-sky ideas about the
theoretical possibilities I'd like to see possibilities/critisisms towards an attainable project.  Am I
way off base on the ability to create a simple circuit that measures various PWM to enable a set of
ports?  If this is am expensive undertaking then say so now so more time isn't wasted on this topic.

If someone has a simpler idea for attainment of more than 3 outputs then I am all ears.

-Wes

Ralph Hempel wrote:

Lou Sortman wrote:

Thanks for checking this out.  This is important to know.  I assume, then, that the duty cycles
are 1/8 through 8/8 as well as off, which would be 0/8.  Can anybody verify this (with a scope or
something)?  I have long wondered whether the duty cycles were linear or followed some nonlinear
curve.

I have checked this out, and if you use the standard RCX firmware (or other firmware
that uses the RCX ROM, then you get the waveforms you are talking about at 125Hz
1/(1ms x 8). You also get polarity information - oh no, I've said too much.

I thought that NQC used the same firmware as the RIS software, and, therefore drove the ports the
same way.  I guess either the documentation is wrong, or the highest or lowest power level is
missing.

Dave Baum, correct me if I am wrong, but I use the internal RCX ROM code to
do the motor driving for pbFORTH, and I'm pretty sure NQC does the same thing.

In other words, NQC and RIS use the SAME code to drive the ports.

Seems to me that all of this talk about multi-device control assumes:

1. That you REALLY need to do this
2. That the RCX using standard firmware can process information for you
3. That you use non-LEGO software to do the work (legOS,NQC,pbFORTH)
4. That you want to spend a lot of time and money getting it to work

With all of the talk about RS232 converters, and PWM decoders, why not buy a
single board computer and do everything from your PC?

I've been with the group for a couple of years now, and in my early emergence
from the Dark Ages though it would be neat to make a single board computer
for LEGO control. Then I thought about it a bit (I'm an embedded systems
designer with 15 years exp) and decided it wasn't worth the effort, and then TLG
came out with Mindstorms. I have always maintained that "neat to do" was fun
until it became a mishmash of technology that was hard to get working. I had
fun doing pbFORTH for the RCX because it did not cost me much except some time
over the holidays. Now I can focus on BUILDING stuff, instead of fiddling and
wishing for things to build.

If you still want to do this, go ahead, we'll support you as much as possible.

Cheers,

Ralph Hempel - P.Eng

--------------------------------------------------------
Check out pbFORTH for LEGO Mindstorms at:
<http://www.bmts.com/~rhempel/lego/pbFORTH/default.html>
--------------------------------------------------------
Reply to:      rhempel at bmts dot com
--------------------------------------------------------



Message has 1 Reply:
  RE: Why do it? Was: multi-device output controller
 
(...) Measuring PWM is not difficult, but it would involve a micro (PIC12C508 anyone?) dedicated to the task and then you would have to get it to drive the RCX, which means motor drivers, etc. If you are willing to spend $50 and LOTS of time, then (...) (26 years ago, 27-Mar-99, to lugnet.robotics, lugnet.robotics.rcx.pbforth)

Message is in Reply To:
  Why do it? Was: multi-device output controller
 
(...) I have checked this out, and if you use the standard RCX firmware (or other firmware that uses the RCX ROM, then you get the waveforms you are talking about at 125Hz 1/(1ms x 8). You also get polarity information - oh no, I've said too much. (...) (26 years ago, 26-Mar-99, to lugnet.robotics, lugnet.robotics.rcx.pbforth)

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