Signaling/Digitrax SE8C Signal Decoder

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Summary: The Digitrax SE8C is a powerful plug and play signal decoder. It makes the addition of prototypical signalling to your layout easy. It can drive as many as 32 signal heads.

Digitrax SE8C

Some consider this unit to be very powerful despite not having any logic to it. According to Digitrax's website, "to realize the full feature potential of the SE8C you will need a computer and compatible software."


The SE8C has the ability to control up to 32 signal heads (four on each of the eight ribbon cables), eight turnouts (more, if you wire slow motion switch machines in series or parallel), and handle up to eight sensor inputs.

Because the SE8C can also control 8 slow motion switches, this might save you some money in not needing additional stationary decoders to control the actual switches.

The biggest drawback on the SE8C is that there is no logic. You can control it manually with the proper throttle but it is an extreme pain. Another option is a logic board. If you are running automation software, the best choice is to use a computer and software. It is really super to have all the signals operate correctly and automatically as the train travel across all SE8C boards.

Considering all that the SE8C is capable of, there is a lot of bang for the buck with this board. For the cost of enough stationary decoders to control eight turnouts (crossovers), you can purchase the SE8C, and basically get the signalling thrown in for free.

Power Requirements

To use the SE8C, you will need a 12v AC or 15v DC power supply with 100ma per SE8C you wish to power. If you are connecting slow motion switch machines, you will have to add them to the demand on your supply as they draw their power from the SE8C board power.

Controlling Signals

Since the SE8C doesn't contain any logic, you need a method for controlling the lights. The two primary methods are manual control with buttons/switches. The second, more advanced method, is through the use of computer software which communicates through the LocoNet of a Digitrax system.

Manual Control - You can add local turnout control by installing a momentary contact pushbutton on a control panel or the fascia if you so desire, or use the throttle to dial up the switch address to throw the turnout.

The manual method is difficult because of how the SE8C works. To throw a turnout with your throttle, push the SW button, select the turnout number, then c or t to close or throw the turnout.

The SE8C uses this method to manually change the signals.

For example, the default value for the SE8C Driver 1 (Plant 1) assigns the turnout numbers 257 and 258 to the first A1 signal head and so on as listed on page 7 of the manual. To change this upper head from red to green you select on the throttle SW 257 and send it a close command. To change to yellow you select SW 258 and give it a thrown command. Then you set the bottom signal with SW 259 and 260 and the the opposing signals with SW 261, 262, 263, and 264. A real pain.

If you want to add signals, a computer and proper software is highly recommended.

Logic Board - A Team Digital SIC24 logic board can be used to control an SE8C. Until someone updates this page, please see their site for details.

Automated Control - LocoNet will need to be connected to the SE8C so that it can be controlled via throttle or a computer with compatible software. You will need block detection, however, transponding isn't required for signalling to work.

Connecting the SE8C

In the middle of the SE8C board are eight sets of 10-prong drivers. Each one controls 4 signal heads. This is called a plant. It can be used for a double 3-head signal that is referred to A1 and A2. This faces a train going into the points. Top signal is main line and bottom signal is branch. The third signal (refferred to as B) faces a train along the main line going into the frog. The fourth signal faces a train coming from the branch referred to as D. Each one of these plants (8) require one 10- wire ribbon cable with connectors for the SE8C and each signal (four in the above case). There are 8 so you can have 32 three aspect signals.

It's best to get ribbon cable in bulk and connectors and make your own custom length cables as needed. Be careful when crimping the connectors on. They MUST be square with the cable and crimped with an even pressure, but not too much. A bad crimp can cause one or more aspects of a signal to not work. Test the cable first with the supplied test mast before installing. This will avoid frustration later.

If you look closely at the circuitry shown in the SE8C manual, you'll see that there's no real need to treat the relationships between the various signal heads as "suggested" in the manual. If you want, each of the 32 signal heads can be set up as a totally independent 2, 3, or 4-aspect signal, depending on how you configure the SE8C and wire your signal heads. Please see the manual on how to configure the SE8C.

The 44-pin edge connector is for detection and turnout control. Inc luded on the connector are pins to control 8 turnouts, pins for 8 facia pushbuttons to control them, the high common for those pushbuttons, 8 sensor inputs for use with external sensors, such as a BD4, and the power inputs.

To make practical use out of all those connections, many users will extend those pins out to a terminal strip, This makes it much easier to make any changes later and troubleshoot if needed.