For automatic control use Current Sensors

Model Railroader Layouts and layout building
1

Current Sensor Control of Trains and Accessories
by Dennis Moriarty (9/1/96)rev.1

Most model train control systems use the location of one or more of the trains to automatically activate other functions.

A few of the functions can be:

  1. Starting or stopping other trains
  2. Activation of signal or other lights
  3. Changing the polarity of the track to change to forward or reverse
  4. Changing the polarity of the track so that trains can run both directions on the
    same track
  5. Activation of track switches
  6. Activation of road crossing gates
  7. Activation of sound systems
  8. Activation of other accessories
  9. Automation of the main line leaving more time to manually operate yards,
    sidings etc.

Some methods commonly used to locate the trains:

  1. Photocell light detectors
  2. Reed switches buried between the tracks with magnets on the engines
  3. Computer control systems
  4. Feeler wires and micro switches

The above methods all have common problems.

  1. They all require a lot of extra wire to be run out under the layout.
  2. They are expensive.
  3. Some like feeler wires can cause derailments.
  4. Reed switches require magnets on the trains.

The advantages of the current sensor approach.

  1. The system uses existing wires to the track blocks so it doesn’t require
    extra wires except to accessories.
  2. Is simple to use and work with once you understand how it works
  3. It doesn’t require knowledge of electronic chips although they can be used if
    desired
  4. Parts and other materials are easy to obtain at local stores. The parts are
    inexpensive locally and are even less expensive if obtained from surplus
    stores.
2

This is very old.

Using one or two transistors with the diodes to make a single or Twin-T circuit is also old but a much simpler way to detect current on the track. Further it doesn’t necessarily need an old mechanical relay. All the DCC manufactures now make various detection circuits. The NCE model uses induction to detect the current so there is no physical connection between the two wiring systems.

3

thnx for the info once and if ever i finish my layout i was thinking about using detection as signaling on my layout it wont be a evry big one so it should be easier to work with. this helps Thnx for post