Logic Diagrams

Logic Diagrams for The Three Configurations of Controls

All three of the systems described on this website use the simple concept of stopping trains in a yard area (one, two, or four tracks) until a train on the mainline travels about 2/3 of the way around the loop; then they "release" a train from the yard.

Note that you can build systems with number of tracks -- from 1 track to 4 tracks or more, using the same basic logic.

Fig a - One Track - Automatic Block

Figure a below shows the logic for a One-Track block controlling two trains.

Fig g - Two Tracks - Automatic Switching Block

Figure g below shows the logic for a Two-Track Automatic Switching Block, controlling three trains.

Four Tracks

The four-track Zellner Yard, is essentially an extension of the two-track Automatic Switching block, increasing the capacity from 2 tracks to 4 tracks.

Zellner Yard, at the moment, does not have a logic diagram on this page. The "Sequencing Schematic", the last drawing on the drawings page, shows part of the logic.

Variations

Fig d - Two Tracks - Automatic Passing Siding

Figure d below shows the logic for a Two-Track Automatic Passing Side, controlling two trains. (If the block part of the Automatic Switching Block shown in Figure G is shut off, then it operates as an Automatic Passing Siding.)

Fig j - Two Tracks - Automatic Route Selection

This is a variation of the Automatic Passing Siding. It's not discussed any further on this website, but is demonstrated in the videotapes.