Just a thought
If you position the pic '508 / 202 in the train then the speed and id can be
generated local to the sensor and teh data transmitted in packets with a
checksum a single receiver and display could then display info from many
trains. This does away with complex modulation to transmit simple pulses and
provides data verification in the form of a checksum or couple it to the
track (same difference the checksum is the verification)

Rgds Steve

-----Original Message-----
From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On Behalf Of
Paul James E.
Sent: 14 February 2006 09:10
To: piclist@mit.edu
Subject: Re: [EE] Speedometer for the model railroad - RF or IR?


 Thats the neat thing about modulating a signal.  You can modulate it so 
 that noise cannot immitate it, therefore, the receiver won't be confused.
 And there are filters.  It's worth a shot in my opinion.  And besides,
 whats to say that the same noise, if any, wouldn't interfere with RF too.
 Just a thought.  I had planned to use this method with my brother-in-laws 
 HO trains, but he moved and I didn't get a chance to get it all together 
 before he moved.

                                               Regards,

                                                 Jim


>>  Why don't you build a small transmitter operating at say 200Khz
>> or so and capacitively couple the modulated signal to the rails
> 
> That thought occured to me initially but I wondered about the amount of
> electrical noise from the motor(s) going back on to the track
> 
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