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PICList Thread
'Model RR and DCC'
1996\04\28@204447 by Prashant Bhandary

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I am confining all my replies into one long post to reduce irritation
to non-RR types on the PIC list...

When I wanted to get back into microcontrollers after using them
8 years ago, I finally narrowed it down to the PIC 16C84 largely
because I thought it would be an IDEAL chip for DCC. Building
a DCC decoder has been my ambition for a while.

The PIC's great for this application as
1) It is available in an 18 pin SOIC. Space is at a premium and
  it is a lot smaller than the 0.4"x0.4"x0.8" suggested by
  John Payson. I would say it is about 1" x 1" x 0.2". Remember
  the loco is already full of other stuff like the chassis, motor,
  etc and you are left with whatever space that is available. And
  John, as for your suggestion to switch to O guage, I really envy
  the guy using the PIC to open and close train doors! Bet he doesn't
  have any space problems with the 1:1 scale he is operating in :-)
  The 18 pin DIP is also great for breadboarding as some of the other
  chips come in a PLCC which is a pain.

2) It's got EEPROM. This is essential for storing the last settings
  without which no decoder is useful. Having to add an external one
  makes things a lot more difficult.

3) The ISP feature which is a boon for any circuit using SMT. There
  is no other way to upgrade the software short of a messy desoldering
  job which can be done only so many times before trashing the PCB.

4) It is fast and requires hardly any external components. To answer Roger
  Books question, the speed is necessary because the info is digital
  packets with an approx bit time of 100us. In fact, I would use a 10MHz
  part if I could find a single quantity source.

And here are some replies to assorted points raised.

There has been some discussion on protocols and a valid point about using
your own instead of slavishly following standards and resulting in code
bloat. I feel standards have their own place as a guide. They are usually
quite thorough and handle situations you may not anticipate. They are
also a good source of ideas. For example, I haven't seen a good multi-master
protocol yet. The CAN standard, though not practical for a simple PIC
implementation, does have a cool arbitration protocol which may be ideal
for multiple PICs. Some day I shall look at implementing that...

The DCC standard is however different. You have to be largely compatible
with the standard. I do find the decoder a little daunting to build and
may buy it off the shelf, for example. You do have the choice of not implmenting
some part of the standards if you don't think you'll use it. Mike Keitz
suggest a smart lamp post. This is being done to some extent. Once you have
a single DCC signal, it makes sense to use it to drive every other accessory
on the layout - switches, lamps, sound decoders... So a smart lamp post does
exists. There is, however, room for a smart dog :-)

I don't see myself using any other approach as DCC seems to be fairly
comprehensive. The only problem with it is lack of feedback. The standard,
as it stands now, just supports a single pulse response from the decoder
though it does have scope for a more complex response. If you want to see
the standards you will find them at http://www.tttrains.com/nmradcc/s91.html
and http://www.tttrains.com/nmradcc/s92.html. If you are doing something in
this area and would like to share experiences/circuits/software get in touch.
May be we can have our own mailing list or web site and stop bothering the
PIC list :-) Shel Michaels mentions writing some DCC software for the 16C74.
Can it be used on the 16C84 or is the capture/compare essential? In any case
would you like to share the code or perhaps plant it in your garden :-)
Although there are a few manufacturers' DCC pages I have yet to find a
'roll-your-own' site. Has anybody seen anything on the WWW on this?

John Payson wrote:
> Normally my inclination for controlling a model railroad would be to use a
> single power-switching transistor and a direction-switching relay.  When
> space is not a problem, this will save components and may save cost (esp. if
> you'd want to opto-isolate things).  In your case, however, there isn't really
> room for a relay. :-(
I did use that approach while building a block control circuit. I soon
switched to an L293. The cost is roughly the same and the size is a lot smaller.
You can also sense the current for occupancy detection or short circuit. One
chip gives you 4 block which is ideal for 1 PIC to drive.

Regards

Prashant
+----------------+  -------------------------------------------------
|                |    Prashant Bhandary
|   +---+        |    Spatial Information Systems Section
|   |   |        |    Roads and Traffic Authority
|   |   |        |    Rosebery NSW 2018, AUSTRALIA
|   |   |        |    Tel:  +61-2-662 5299
|   |   +----+   |    Fax:  +61-2-662 5348
|   |        |   |    Email: spam_OUTprashbTakeThisOuTspamrta.oz.au
|   +--------+   |
| Still a newbie |    "2b|!2b" - William Shakespeare
+----------------+  -------------------------------------------------

1996\04\29@125507 by Odriozola Belden

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Digi-Key sells 10 mhz 16C84's in single quantity (from 12.10 to 13.30 US Dlls).
phone 1-800-digi-key
fax     218-681-3380
http://www.digikey.com



At 10:43 AM 29/04/96 +1000, you wrote:
{Quote hidden}

implmenting
{Quote hidden}

really
>> room for a relay. :-(
>I did use that approach while building a block control circuit. I soon
>switched to an L293. The cost is roughly the same and the size is a lot
smaller.
{Quote hidden}

1996\04\29@130729 by Mark A. Corio

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Hi all,

Prashant suggested moving to a new list to keep from boring the PIC people.
I for one, hope you do not.  A list that discussed only the technical nature
of the PIC parts, without discussions of the applications in which they are
used, would be boring.  Some may disagree with me but I like the discussions
that go into the application areas.  This thread is a good example.  I could
never have predicted some of the application areas that the PIC has gone.

Keep the application discussions going.....my 2 cents.


Mark A. Corio
Rochester MicroSystems, Inc.
200 Buell Road, Suite 9
Rochester, NY  14624
Tel:  (716) 328-5850
Fax:  (716) 328-1144
e-mail:  McoriospamKILLspamaol.com

***** Designing Electronics For Research & Industry *****

1996\04\29@132811 by Odriozola Belden

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I agree with Mark, the application discussion is as important as the tech.

Rogerio



At 01:06 PM 29/04/96 -0400, you wrote:
{Quote hidden}

1996\04\29@133224 by Ben L Wirz

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I also carry 10 Mhz 16C84's for what I believe is the cheapest price
available on the Net in this quantity:

$8.50 USD for less then 10
$9.00 USD for 10 or more.

See my WEB page for more details.

Ben,

Ben Wirz                Check out My Home Page for Great Deals on Bulk Buy's
                       Nitinol Wire, LMD 18200 H Bridge and 10 Mhz PIC 16C84
EraseMEblw2spam_OUTspamTakeThisOuTcec.wustl.edu      http://cec.wustl.edu/~blw2/index.html

On Mon, 29 Apr 1996, Rogerio Odriozola Belden wrote:

> Digi-Key sells 10 mhz 16C84's in single quantity (from 12.10 to 13.30 US
Dlls).
{Quote hidden}

1996\04\29@150212 by Brian Boles

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    Ditto from the factory.  We try to do as much research into
    applications as we can to better understand how to configure our
    products. These application discussions are a wealth of info for us.

    We are doing visits to companies doing industrial machine/process
    control now.

    Rgds, Brian.


______________________________ Forward Header __________________________________
Subject: Re: Model RR and DCC
Author:  "Mark A. Corio" <Mcoriospamspam_OUTAOL.COM> at Internet_Exchange
Date:    4/29/96 1:06 PM


Hi all,

Prashant suggested moving to a new list to keep from boring the PIC people.
I for one, hope you do not.  A list that discussed only the technical nature
of the PIC parts, without discussions of the applications in which they are
used, would be boring.  Some may disagree with me but I like the discussions
that go into the application areas.  This thread is a good example.  I could
never have predicted some of the application areas that the PIC has gone.

Keep the application discussions going.....my 2 cents.


Mark A. Corio
Rochester MicroSystems, Inc.
200 Buell Road, Suite 9
Rochester, NY  14624
Tel:  (716) 328-5850
Fax:  (716) 328-1144
e-mail:  @spam@McorioKILLspamspamaol.com

***** Designing Electronics For Research & Industry *****

1996\04\29@193452 by myke predko

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I agree.  I'm not a railroader, but I do enjoy the discussions!

Myke
{Quote hidden}

Myke

"We're Starfleet officers, weird is part of the job."

Capt. Catherine Janeway


'Model RR and DCC'
1996\05\01@130745 by Martin McCormick
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       I agree with all the others.  I don't do model RR's, but I appreciate
a good technical discussion any day.

       Is the DCC signal anything like X10 control signals?  With X10, we
have a 120 KHZ CW signal which sends digital codes over the AC mains to X10
receivers in the building that can turn power on or off to devices or regulate
light levels.

       For many reasons, I enjoy the discussions by all the people about their
different projects because most of them know more than I do and I appreciate
the intelligent discussions.

Martin McCormick WB5AGZ  Stillwater, OK 36.7N97.4W
OSU Center for Computing and Information Services Data Communications Group

1996\05\01@202051 by Ram Krishnan

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"Prashant suggested moving to a new list to keep from boring the PIC people.
I for one, hope you do not.  "


I second you on that - The very universal nature of the PIC microcontrollers lends their use in a wide variety of applications, and what's being used in the Model RR today may find use in a CCD camera tomorrow.

RK

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