Re: Automatic Train Control

Vollrath, Don <dvollrath@...>

re - position fedback
2 or 3 possibilities:
1) Use electrical current detection at separate sections of the track from loco/tram occupation and/or each car. break track up into insulated detection blocks. Detect small current drain at each block. May require conductive axles on each car. Occupation detector output signals report back to master computer or local signal operating apparatus. Requires insulated rail gaps & electronic current detectors for each block.
2) Use magnetic passage scheme with magnetic reed switches at specific points along the track path. Tram and or cars have under carriage magnets to activate switches. Since switch activation would be momentary, master computer must keep track of which switch is being passed and direction from last detection. A "spot" location sensor like this is useful for a specific location, like crossing signal activation. Magnets attract 'metal dirt'.
3) Optical version of #2 with visible or infra-red light beam. May operate as across-track blockage type or reflection of beam off side or bottom of rolling stock. Simple opto-sensors use train shadowing of room light and therefore won't work in the dark. Some electronics required either way. Could also use ultrasonic detectors in similar fashion.
4) Use combination of scheme #1 with #2 or #3. Place optical sensors at both ends of electrical detection blocks. Diode couple signals to 'Wire-OR' the block end sensors with the output of the track current sensor for that block. Now block occupancy will be detected as loco with current draw has left block but rear of train is still occupying the block without need for conductive axles on rolling stock (!).

The above schemes will work with DC or DCC with proper choice of apparatus.

5) For DCC only, use Digitrax or other brand transponder idea. Requires: a) insulated track blocks with transponder type reciever wired to each block; b) transponder in each loco/tram or car to be detected; c) computer to gather transponder indications and keep track of train/tram locations. Available equipment is brand dependant.

6) Track current detectors also come in many flavors. Some work with DC, some only with DCC, some can do both. Some are isolated from track power, some not. Many have universal 'open collector' type outputs and can be used with 5V or 12V signaling. Some are 5V only. Be careful to pick the right one.

My choice is #4 with track current sensors and reflective type IR spot sensors.
Your automated tram application would be greatly simplified if you provided a reversing track loop at each end of the display rather than having the tram actually run in the opposite direction.

re - crossing signal activation
Your requirements are not too difficult. Requires 3 short block occupancy sensors at grade crossing to detect train approaching from either direction and to detect when it leaves the crossing island. Simple logic and timers do the rest. If you have computer, use that to perform logic and provide bell sound. (Bell doesn't remain ON when gate is down??). Check Dallee electronics (and others) for commercial equipment. A couple of '555 timers cam be made to do all without a computer. See future article in Clear Block.


-----Original Message-----
From: WiringForDCC@...
[mailto:WiringForDCC@...]On Behalf Of Jan Frelin
Sent: Thursday, July 14, 2005 4:17 AM
To: WiringForDCC@...
Subject: Re: [WiringForDCC] Automatic Train Control

We're still considering a DCC solution, not in the least because of the
opprtunity of controling some accesories with the computer while you're at
it. Thus I have some followup question to this list:

1) What are the options for arranging feedback regarding stock position
with DCC? The basic scenario is still a tram going back and forth between
two locations.

2) We require a pair of working crossing gates, which need to do the
following: a) start ringing bells to warn traffic. b) start closing 10
seconds later c) grow silent when down d) open silently. An interesting
automation project. Any ideas?


At 11:18 2005-07-01 -0700, Mark Gurries wrote:


My club has a requirement for a tram that just goes back and forth
between it's terminal track and staging/storage. We want this to be
automatically controled. There are several kits for doing just this on
the market, but all I have found are DC based. As this track is
connected with the general layout, we would prefer a DCC solution, but
this seems to require a computer, a computer interface, and track

My question is: Is there a simpler solution with DCC? What's the
cheapest DCC-based solution (without building your own hardware or
Nothing is simpler or more cost effective than a DC solution.

DCC has layout automation software for DCC.


is an example of such software.

But you will need a computer, a computer interface to the DCC system,
sensors in the track (DC will need that too) and do some programming.

Definitely more expensive and requires a computer running to make it
happen. The DC solution would be hands off easy to setup and forget.

Some thoughts...

Generally mixing DC and DCC is not recommended by anyone. I can result
in destruction of a booster, DC throttle or both if both power sources
connect to each other. (DCC is a form of AC power) If you must run DC,
the recommendation is that one have a master switch that toggle the
whole layout between DC or DCC but NEVER both at the same time. Many
layouts have done this successfully. There was an article about how one
club did it in MR magazine.

If you MUST have DC and DCC present, there are some recommended rules.

1) Isolate at least a 12: section of track the goes between the DC power
section of the layout and the DCC powered portion of the layout. A no
mans land with not power. Using a momentary center off switch, you
would toggle the power of the dead section of track to DC or DCC
depending on which side of the dead section of track you need to get
power from. The key is momentary switch. A standard toggle will no be
safe for you will forget to turn it off.

2) Another option to isolate the approach track from the DCC portion of
the layout and power it through a Lenz LT100.


The LT100 is connected to your DC power pack output. It monitors for
signs of DCC and will instantly disconnect the DC power pack from the
track protecting both system.

I should say that running a locomotive from DC section of track to a DCC
section of track can lead to a runaway locomotive. Most decoder make a
decision on first power up to run in DCC or DC mode. As long as power
is maintained, that decision remains true. So if the decoder see DCC
power after while it has been running in DC mode, the decoder will not
recognize the DCC and assume the DCC is nothing more than full throttle
DC power and vrooom.....

The reverse DCC to DC is less predictable. The engine may simple stop
and not run OR switch to DC mode with a very erratic reaction in the

Part of the randomness to all this is the nature of an engine rolling on
track with the corresponding momentary loss of power. Dirt, oxidation,
clean wheel, number of wheel pickups and other such factor play into the

Best Regards,

Mark Gurries
Linear Technology
Power Supply & Battery Charger Applications Engineer/Manager
Model Railroad Club and NMRA DCC presentations are at:
Audio Enthusiast (Love SAE equipment)

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