Robot - Micro Data Transmission over 12 volt line

sswcharlie wrote:

All over the internet and manufactures data sheets where there is a
proprioty protocol ;o)


Is this 12 for signal only or are you looking at 12 power with a
modulated signal?

Are you interfacing with existing equipment? If so what is it?

Is it an RS232 (+12v / -12v) you need? You'll find that there are a
number of devices to give simple interface search for "RS 232 Driver".

regards,
Colin

Hi Collin

Thanks for your email.

Firstly I am a beginner on PIC !

I am getting assistance on the two PIC modules, it is just the putting
of the signal across the 12volt dc.
Basically the two modules could be hard wired together but in this
case the decoder moves around and I want to use the track to send the
signal to the decoder where ever it maybe.

It is for use on a standard model railroad (form of robotics!) layout
using variable dc up to 12 volts.

The signal is required only 1 way - from kepad PIC connected to the
track or power supply,  across the track to the decoder PIC mounted in
a passenger car and connected via wipers to the track.

Message is to just turn leds on or off.

Distance - probably should work on  10 metres max. but varies as the
passenger is moved around the layout etc.

Locomotive control is not wanted, just using standard dc voltage
conroller.

Your comments are appreciated.

Thks

Charlie

Because a standard model train picks up the power from physical contact
with the tracks, and because the wheels and train is moving, you can expect
there to be a lot of noise in the signal.  That's going to make encoding a
signal even harder.

Add to that the fact that the track makes up a lot of unpredictable
contacts in the circuit from track segment to track segment, and the fact
that the DC voltage is going up and down as the speed of the train is
changing, and it all adds up to a tricky problem finding a way to encode
the signal and not have it confused by the normal operation of the train.

I'm not sure, but don't the standard cheap train power controllers use
rectified but unfiltered DC to begin with?  If that's the case, you might
have a 120 Hz pulsating DC on the track to make things even harder.

You will need some system which includes a lot of redundancy in the signal
in order to factor out the potential noise already in the power circuit.
There are a million ways to do that, but I don't know much about what is
available off the shelf to help you.  It's not a typical problem which I
would expect there to be an off the shelf solution available.  But maybe
someone here with more experience with PIC I/O devices could suggest
something?

One path is to use an RF modulator to put the signal into a fixed frequency
band. AKA, broadcast it like a radio signal using AM or FM modulation over
the wire.  That might be had off the shelf, but still be usable over the
track.

--
Curt Welch                                            http://CurtWelch.Com/
curt@kcwc.com                                        http://NewsReader.Com/

I am sure we are talking about an extreme amount of electrical noise.
You might use an off-the-shelf radio frequency remote on-off switch.
Or hack one out of a radio-control toy.  But, the electrical noise may
make those systems inoperable.

Perhaps better way is to use an Infra-Red signal, like in your TV
remote control. I am sure there are kits for this.  In fact, I am sure
there are versions, done just for PIC's, that would allow you to do
more than just a single on-off.

Joe Dunfee

sswcharlie wrote:

    There's a standard, established technology for this, called "DCC",
standardized by the National Model Railroad Association.
See "http://www.nmra.org/beginner/dccbasic.html"

    Here's the electrical level interface standard.

http://www.nmra.org/standards/DCC/standards_rps/S-91-2004-07.pdf

Here are some available parts:

http://www.modelrectifier.com/search/advanced-search-results.asp?Category=TRAIN%20CONTROLS&SubCategoryÜC

                John Nagle

sswcharlie wrote:

I spent some time on the same problem before giving up
on it.  The bad news is that I never got 100 percent
reliability on it.  The good news is that the best I
got was pretty good and only cost $3.50.

I bought a Radio Shack consumer IR receiver like those
that receive IR remote control signals.  I disassembled
it and removed the IR photo diode (or photo transistor)
and connected the leads that went to the photo diode to
two capacitors that were connected to the track.  At
the transmitter I had an AVR sending out regular IR
signals (like that found on a Sony remote control)
through two capacitors connected to the track.

So, capacitively coupled 40 KHz transmitter, the track,
and a capacitively coupled receiver that has an AGC
and 40 KHz detector.

hope this helps
Bob Smith