208-S Ga. 2-Track Auto. Switching Block

UPDATE Jan 2009: A Project 208 page has been added
showing Nov 2008 photos of the as-built unit.

Project 208 - Notes, July 2008

Note: The next-to-last drawing on this page (Image 4 down below), shows the preliminary wiring diagram.

A. Overview
  • This web page describes some preliminary work on an S-gauge "Automatic Switching Block", using American Flyer track switches. This system will control up to 3 trains on 1 track. It should work with AC, DC, or DCC; since it uses simple, open/closed relays for stopping, and rheostats for "slowdown" sections.

  • Brand Of Switches -- The plans on this page, use the old American Flyer switches, that require a lot of current. If you used a newer, different brand of track switch other than American Flyer switches that required less current, that did not have such enormous (6 amps per pair) amperage requirements, then you could probably use one of the electronic switch control units, such as the Railroad Concepts "SwitchMaster".

  • No Data On Other Brands of Switches -- I don't believe there is much data on how well the various brands of S gauge switches will operate in an automatic control system like this. Dennis Oberholtzer and Mark Anderman demonstrated in their video that it can be done with the original AF switches. I don't think anybody really knows how the other brands will function when used in this kind of application.
  • Operate Sidings Only -- The "block" part can also be "powered-down" to operate 2 trains in the traditional "Automatic Passing Siding", where 1 train pulls in on the 1st siding, and then the other train pulls out.

B. Related Videos
  • There are already YouTube videos that show parts of this system, as follows:

  1. The YouTube AutoControls Video #1 "How-It-Works 2-Track Auto. LGB Yard" shows a LargeScale Automatic Switching Block in various operating modes using just 1 train, 2 trains, and 3 trains.

    The S gauge system would use the same logic; we just need to "replicate" it in S gauge.

  2. The YouTube Video "Susquehanna S Gaugers 'Steamup', Automatic Control" made by Mark Anderman, shows a similar system operating in S gauge. But in this video, they used the American Flyer pressure-sensitive track contacts, and they used a 3rd block on the mainline to stop the 3rd train. [click here for wiring sketch and notes].

    For the system shown on this web page, we plan to use reed switches instead of the AF track trips, and we plan to eliminate the 3rd block.

  3. The AutoControls YouTube Video #8 " S Ga. Auto. Block Using RR Concepts SIM" shows a plain S gauge Automatic Block in operation. The plans shown below incorporate the same Railroad Concepts "Switching Interface Module" (essentially a Double-Pole Double-Throw {DPDT} latching relay) to handle the "block" part of the operation.

C. Mark Anderman's Demo Unit

Click on any of the below images to
open it LARGER size.

Image 1 - Mark Anderman's Demo Unit
  • The above photo shows a demonstration unit built by Mark Anderman, using reed switches and automotive relays with rectifiers to activative an American Flyer switch. Note he used relays, because some of the electronic switch controllers probably would not work with an American Flyer switch, because of its high amperage requirements.

  • Using Michael Green's "Getting Started with
    NMRA DCC with specifics & examples for S Scale
    " (a PDF doument published in 2002, available from the DccInfo.com's 'Clinic Handouts' web page) as a reference source; the document states on page 27, "American Flyer remote control turnouts draw over 3 amps to throw the turnout, and American Models remote control turnouts draw approximately 1.25 amps". Therefore operating a PAIR of AF switches for this siding would require about 6 amps.

  • Mark has been selling some of these relay & rectifier assemblies on eBay -- look for user 'manderman'.

Image 2 - Mark Anderman's Drawing for AF Switch Control
  • The above drawing was made by Mark Anderman, and shows the wiring diagram for hooking up a pair of American Flyer switches, controlled by reed switches and relays.

D. Logic Diagram

Image 3 -- Logic Diagrams for Automatic Train Control
  • The above drawing shows the "Logic Drawing" for an Automatic Switching Block. The 3rd diagram on the drawing, 'Figure G', shows the logic for controlling 3 trains. Parts of the control can be turned off to control 2 trains using either the block-only or sidings-only, as shown by the 1st two diagrams on the drawing.

  • Video Demos - The first 3 modes are demonstrated on the above-referenced LargeScale Video #1 How-It-Works. The last mode, "Automatic Route Selection", is demonstrated in LargeScale Video #6 "Automatic Route Selection".

E. Wiring Diagram (Preliminary)

Image 4 -- Preliminary Wiring Diagram
for S-gauge Automatic Switching Block
  • The above drawing shows a PRELIMINARY wiring diagram, using American Flyer switches. WARNING: This drawing may have some minor errors in it, and needs to be tested.

F. Additional Comments
  • Note the terminals 17 through 24 and the SIM (Switching Interface Module) are for the blocking part. For just the switching function, you could eliminate all these wires and the SIM, and connect Wire #37 coming from the Startup rheostat to terminal 15, which would be the same as putting the block permanently in the green position.

  • Note Terminals 14 is "reserved" to go to the other siding, if we used some other type of switch that was non-power-routing. We'd also need to add a 2nd SIM or latching relay to route the power to the proper siding.

  • Note my notes show DC track power, but AC or DCC could be used as well.

  • For this design, normally the gaps would be only in the right (+ rail. (It would also work if the left (-) rail had the gaps)). But I think we need gaps in BOTH rails, by the curved leg of the switch, because the switch wants to "kill" the inside rail to stop the train when the switch is straight, and if there was not a gap in the left rail, current would come through from the other switch.

Image 5 -- A similar control unit for a G-gauge
Automatic Switching Block (from Plans Folder 206)
  • Note in the unit shown in the above photo, LGB switch motors & plug-in DPDT relay points were used for controlling both the siding and the block. In contrast, the S-gauge unit uses automotive relays to control the siding, and a Railroad Concepts SIM to control the block.

(Project Folder #208)