Inglenook Sidings

This project combined my interest in electronics and computers with model railroading. Its main feature is an automatic mode that operates the engine and turnouts to reverse a sequence of train cars. An unintentional feature was perhaps an answer to the question of why serious modelers avoid automatic uncoupling. It's difficult to get it to work reliably, especially in N-scale.

To improve reliability electromagnets were used for the uncouplers instead of the more common permanent magnets, which can uncouple cars when not intended.

The Kadee 708 electromagnets are designed for HOn3 and fit N-gauge track. I modified the suggested assembly by insulating the field plates from each other to prevent electrical shorts. I also eliminated the bulky mounting plates by simply hot-gluing the electromagnets into the layout. This is explained below.

To prevent the engine from stalling at slow speeds Peco turnouts with electrofrogs were used. They are actuated by Tortoise servos, which are quieter and more realistic than solenoids.

To further reduce the possibility of stalls, the steam engine has additional electrical pickup in its tender.

Cars with the most reliable Micro-Trains couplers were selected. Each car has a super (neodymium) magnet mounted under it that activates reed switches hidden in the track. These detect when a car is positioned over an uncoupler or has cleared a turnout. Many different kinds of magnets were tried before suitable ones were found.

The backdrop is a photograph taken with an 8-megapixel (Canon A720) camera east of Boulder Colorado. Mike's Camera made the print for $38.

The layout is designed to operate the standard 3-3-5-3 puzzle, but a scaled-down 2-2-3-2 version has proven to be more suitable for train shows where visitors have only a limited amount of time to watch.

Electromagnetic Uncouplers for N-Scale

The couplers are the Magne-Matic kind like used on Micro-Trains cars, not the Rapido kind used on less expensive equipment. The Kadee 708 uncoupler is designed for HOn3, which fits N-gauge track.

The main problem with Kadee's installation is that it's likely to cause a short circuit. Another problem is the bulky mounting plates. These prevent mounting uncouplers side-by-side on closely spaced sidings, and they're difficult to conceal.

As you can see in the diagram there's very little space (if any) between the field plates on the uncoupler and wheel flanges. The metal wheels on an engine will likely touch both the rails and the field plates simultaneously; and since the plates are electrically connected, this shorts out the track. One solution (which is extensively explained on the Internet) is to increase the space between the plates and the rails by bending the plates, but that's difficult to do accurately, and it also requires that all couplers be readjusted. I chose instead to insulate the field plates from each other. Here's how:

Make a pair of paper washers from a 3x5 index card. Draw two circles on the card using the uncoupler's cylindrical core as a template. Cut the circles out slightly larger than the core. Punch holes in the centers with a standard 1/4" paper punch. Replace the metal bolt and nut that comes with the uncoupler with a nylon bolt and nut (a 10/24 3/4" available from McGuckin Hardware).

To reduce the possibility of the wheel flanges riding up over the field plates, file a 1/8" bevel on the rail-side on both ends of each plate.

Assemble the uncoupler. Insert the nylon bolt into one of the (correctly oriented) field plates. Add in order: the paper washer, the cylindrical core, the coil, and the plastic field plate divider. Rotate the coil so that its notch engages with the plate divider. Add the second paper washer and field plate. Note that the nylon nut has a built-in washer on one side. Loosely screw that side on so that it's in contact with the field plate. Gently tap the field plates on a flat surface to make sure they are exactly parallel, and then tighten the nut.

Burn the lacquer coating off about 1/2" of the wire leads with a match or lighter. Use fine sandpaper to remove most of the remaining residue.

Mounting

Instead of cutting a 2-7/8 x 1-1/16 hole in your layout like Kadee specifies, cut a smaller hole, just large enough to insert the uncoupler from the underside, about 2-1/8 x 3/4".

Cut away 2-1/8" of ties from the center of the track to allow the field plates to be inserted between the rails. Save any tie pieces that fall away so they can be glued on later.

Make a gasket from an index card with a 2 x 3/8" hole that passes the field plates but covers the hole in the layout, and glue it on the layout.

Insert the assembled uncoupler through the underside of the cutout in the layout. Hold it in place while inserting (N-scale 4x8 bass wood) shims to center it between the rails. Cover the uncoupler with masking tape to hold the shims in place. Place a wooden block over the uncoupler, and use it to position the field plates at the same level as the rails.

With the infinite dexterity of a model railroader, from the underside of the layout, apply two dabs of hot glue on opposite corners of the uncoupler to temporarily hold it in place. Closely check the alignment. If it's wrong, a hair dryer can be used to loosen the glue enough to reposition it. When it's correctly aligned, apply more hot glue to hold it permanently.

Operation

The uncoupler coil is 8.5 ohms, which means that will try to draw more than an amp (at 12V), and it will get hot if left on for more than a few seconds at a time. Use a momentary push button rated for 2 amps or more.

Links

Here is a nice Java script that lets you operate the puzzle directly from your browser: http://www.precisionlabels.com/shunt/jpage330.html

The magnets that are mounted on the bottom of each train car and are used to activate the reed switches in the track came from here. They are the smallest ones at the top of the page.

This is the reed switch. The small size makes them easier to conceal. You can buy them here.

Here is a schematic diagram of the circuitry mounted on the underside of the control panel: Schematic.

The heart of the control system is the PIC24FJ64GA002 from Microchip.

Here is the code that runs in the PIC: Inglenook.C

-Loren Blaney

Last updated 28-May-2026