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Posted by Curt Welch on August 31, 2008, 11:29 pm
> 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/
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