Ataras TC4 Three-Color, Four-Block Signal Controller: All Scales

When I say a three-light signal, I mean a signal with a single head, although the head itself may take the form of a semaphore blade, a circle of position lights, three vertical color lights like a traffic light, or a searchlight where a mechanism places green, yellow or red lenses in front of the light. More correctly I should say, the TC4 will control a single headed signal capable of three aspects providing three indications, stop, approach and proceed, as determined by the occupancy of the blocks ahead.

A three-color signal standing at the entrance to a block (a length of track electrically separate from the rest of the layout) indicates red (stop) if the block is occupied by a train or a car; if the immediate block is vacant but the next block ahead is occupied, the signal aspect is yellow (approach); if both blocks are vacant it shows green (clear). If the track is signaled for movements in both directions, there will be signals on either side of the track at a block boundary, facing in opposite directions, indicating the occupancy status of the blocks ahead in each direction.

Should there be one or more turnouts in the block, the signal has to indicate permissible speeds through each route as well as occupancy status. These signals (frequently called "interlockers" because they are interlocked with the the turnout throw mechanism, or "control" signals because they are controlled by signalmen or dispatches) are far more complicated, usually requiring two or three heads to convey the appropriate indications. The TC4 is not designed or equipped to control such signals.

As it is able to control four three-aspect signal, the TC4 needs to know the occupancy status of up to eight different blocks. However, the internal connections within the TC4, controlled by user-set jumpers, can greatly simplify this wiring if the blocks and signals are contiguous or if the track is signaled for only one direction of travel.

The TC4 comprises a 4 inch by 2 inch printed circuit board with major components and terminal strips attached to the top side. It also comes with a 9-volt power transformer and mounting hardware for the board. One terminal strip connects to each of the twelve signal lamps, another to the block occupancy detectors. The signal lamps may be bulbs using up to 12 volts of Light Emitting Diodes. In the case of bulbs, you must provide a separate power supply for them.

You must do quite a lot of preparatory work on the layout between selecting signal locations and connecting up your TC4. The blocks ahead of each signal must be connected to an occupance detector and a minimum of four wires run to each signal. Four strand, multi-color wire, such as Radio Shack 278-757, makes this task simpler and much neater. Incidentally, don't forget to run all your widest equipment past your new signals to check for clearance problems before you wire them up and nail them down.

The TC4 is so versatile that it provides a 27-page instruction book to cover all the possibilities. I suggest you read it through completely to ensure that you consider all the possibilities while you are planning your signal installation. Once I had identified which tables and figures applied to my situation, I copied the relevant pages and cut and pasted them up to provide my own one-page wiring guide.

Connecting the wires to the TC4 takes only a few minutes once all these preliminary tasks are out of the way. Plug in the power transformer, switch on the signal power, and enjoy the green lights indicating clear blocks. Run a train around and watch as the signals change prototypically to indicate which blocks are occupied. Your engineers will love them and demand an end to dark railroading everywhere else on your pike.

I used an Ataras BD16 block occupance detector and NJ International signals. I run the nominally 12-volt bulbs on 8 or 9 volts d.c. from an old power pack to reduce excessive glare from the lamps. This has the added advantage that I have yet to burn out a signal bulb in 25 years of operations.

Simply stated, the TC4 works flawlessly. At a list price of $70.00, the controller is an efficient and cost effective way of extending three-color signaling to appropriate parts of your layout.