SE8C & RR&Co

The SE8C has eight ten-prong plugs on the circuit board (called drivers DRV1 through DRV8). Each of these Drivers accepts a socket that controls four signal heads. This makes a total of 32 heads controlled from one SE8C. They can be almost any type of head as long as you set the option switches of the SE8C to that type of head (explained adequately in manual). Digitrax calls each of these a Plant, and uses the terms A1, A2, B & C for the four signal heads. A1 & A2 are for two heads, one over the other. They face the approach to the points of a turnout, the top head for the mainline track and the bottom head for the diverging route. B faces the opposite direction on the mainline and C faces the same direction as B, except it is on the siding. In actuality, these signals are completely independent of one another. They could just be named #1, #2, #3, & #4.

These heads can be four individual heads anywhere on the layout and each head controlled individually as long as the 10-conductor cable from that Driver is continuous between them. You do not have to use all heads on a plant. I use Digitrax’s TSMK Terminal Strip Mounting Kit (2 come in a kit) which wires two signal heads each for the 4 heads. The terminal strip comes with the 10 pin ribbon cable connector, a 10 wire terminal strip, and 100 ohm dropping resistors between them. (Depending on the leds you use, you may need more than 100 ohms. If so add additional resistance in each control line) I run the 10-conductor ribbon cable from the SE8C to each of the 4 heads without interruption using generic ribbon cable (M-RIBN10 below) because it is much less expensive than the ten color Digitrax cable. A 100ft roll costs less than $15.00. We wound up using nearly four rolls of it. You don’t need all those colors anyway as long as you have one wire marked. I then use a 10-pin displacement connector (M-IDC10) to connect the cable wire to the TSMK and the SE8C. Just crimp the connector onto the ribbon cable at a place to plug into the TSMK (and the SE8C). Wire the signal heads to the TSMK and you’re done with this part.

When crimping the connector, there are three things to observe carefully. First, the connector must be absolutely square with the cable. Second, the connector has an indent to identify pin 1. Make sure that coincides with the red strip. Third, use an even pressure, but not too much, to squeeze the connector closed. Channel locks work well if you set its closed width to the width of a closed connector. Failure to do so may result in a bad crimp causing one or more aspects of a signal to not work, or you will break the connector while crimping. Test the cable with the test mast before installing. I recommend using the supplied strain relief at all connections. This will help secure the connection and prevent it from pulling apart.

In the above picture, a signal (1 of a possible 4) is wired to the High Common and the High Red, Yellow, and Green terminals. That is the B signal. Additional signals can be wired to the High Common and Low switched (C), Low Common and High Switched (A₁), and Low Common and Low Switched (A₂) outputs.

Remember to tell the SE8C whether you are using common anode or common cathode signals. You cannot use both on the same drivers, but you can divide drivers 1-4 and 5-8 to be one or the other if you happen to have both types of signals and wish to use them all. It is generally good practice to use all of the same type.

The SE8C is also capable of detection of eight zones when used with two BD-4s. (In reality, the BD4 has shown to be unreliable, so the suggestion is to not use it) In addition, it can control eight turnout motors, though those outputs were originally designed for semaphores. All in all, a very well designed circuit board, with tremendous capabilities. To control 4 heads and 12 lights with ten wires, Digitrax uses a system of alternating commons (multiplexing). Pin 1 is Common LO and Pin 10 is Common Hi. When you reverse the signal in the socket, Pin 1 becomes Pin 10 and vice versa. Control is sent out from the board for two heads at a time and then reversing the common HI and common LO, it sends out signals for the other two heads. It does this very fast so the eye cannot see the LED’s going out during switching. Plug the signal mast in one way and get A1 & A2, reverse the signal mast and get B and C. This is very ingenious.

This is an SE8C as mounted under one of our modules. The edge connector pins are wired to a terminal strip next to it. It then can be easily wired to other components, and allows for easy troubleshooting when needed. This should be done with all boards that use the edge connectors. In our modular setup we then just plug in the ribbon cables and Loconet and are ready to go. Power to the board is supplied by a PS12.

The turnout motor outputs could also be used to control semaphore signals. When set up that way, the SE8C will send a command to the motor to move to any one of 3 positions; full left, center, or full right to simulate the three aspects of a semaphore signal. So if that's the era you want to signal, it can handle that too.

The SE8C has no onboard logic to set signal aspects. That logic must come from another source that issues programmed switch commands based on the situation. That can come from another board, a throttle, or a computer. The board comes with the default switch numbers 257 through 320 and the 4^th aspect defaults to a flashing Yellow. The default turnout addresses are 1 through 8. The sensor inputs are 1,1 through 1,8. Setting the board ID to a number other than the default 1 will change the signal address ranges, the sensor addresses, as well as the turnout addresses, though there is the option ro set the signal addresses independant of Board ID. The fourth aspect can also be programmed for flashing green, flashing red, or blank for approach lighting*) Each signal head uses two switch numbers. After the signals are set up, you control the lights with switch commands**. This is demonstrated very well in the manual when you do the Pre-installation Testing. For example, Plant 1, Signal A1 will turn Green if you send a closed command to switch 257. If you send a thrown command to switch 257 the signal will turn Red. If you send a closed command to switch 258 (next in line) that same signal will turn Yellow. A thrown command to switch 258 will flash Yellow (default). Plant 1, Signal A2 uses switch numbers 259 & 260. B uses 261 and 262 and C uses 263 and 264. Plant 2 uses the next 8 switches and so on.

* Approach lighting, by extinguishing the lights when no train is present, is used by railroads to extend the life of the lamps. They "come alive" when a train enters a block controlled by a signal. The SE8C can be configured to duplicate that situation.

** Switch commands: An accessory address being sent a command to either throw or close. Signals, turnouts, and any other accessories controlled by a stationary decoder share a range of addresses, up to 2048. No two accessories can have the same address, so be careful when assigning addresses to your accessories. Loco addresses are handled independently from accessory addresses, so there is no conflict between them. Loco addresses can go up to 9983.

First set up your Switchboard with your track, turnouts, and detectors. After you have this part working to your satisfaction, add a two, three, or four aspect signal as appropriate for each situation on the Switchboard. .

Double click on the signal. Under the General Tab, give it a name, (example: Signal 257 named after the first SW# of the signal, or you can name it based on it's location) and then select the image you want to appear on your Switchboard. This image is for appearance only and doesn’t have any affect on the operation.

(A note on names. Train Controller uses the name of a switchboard element when referring to it in the properties or operations of another element. When you first add an element, such as a turnout or signal, TC names it based on its location on your switchboard. If you don't assign a new name that you can remember, and you have a number of them, you will have a difficult time figuring out which one to refer to later.)

Next, click on the Connection Tab. Make sure the system is Digitrax Loconet. Next enter the address. BE CAREFUL. This number must be the FIRST switch number of the SE8C signal head you are trying to control. For example, if your SE8C is board 1 and your 10-wire ribbon cable is plugged into DRV1 and you are using signal A1 of that plant, enter address 257. TC will automatically know that address 258 belongs here also. NEVER enter the second address of a signal. If your 10-wire ribbon cable is plugged into DRV 6 and you are controlling the B signal, enter 301. All these addresses are on page 7 of the SE8C manual. For higher Board IDs, just add 64 to the number for each board numbers above 1.

If you wish, click the test signal until it turns Red and check the box Normal State. It probably defaults to this. Switch time is normally zero. Also make sure the ¾ aspect button is checked. Next is the Output Configuration window. If you selected a 4-aspect signal you should have a Green, Red, Yellow, and White signal showing. White is for flashing yellow for the SE8C, its default. However you can set the fourth aspect to flash any color, or dark for approach lighting. Beside each signal are 4 buttons representing closed and thrown for two switches. It initially comes up as follows, or something similar. The SE8C will respond only to the first switch command sent to it, so having two switch commands in each line won't work. You have to eliminate some.

For Green, we want the first switch to be closed and the second switch blank.

For Flashing, blank out the first T and change the second T to C by clicking on the button where the C is supposed to be.

Do the preceding for each signal you want on the layout. Be careful of the addresses.

The triggers for each signal are now incorporated into the signal properties. Since you can have and/or statements together, it simplifies everything. You can also have the signal aspect displayed differently for the same basic conditions, but based on the direction of travel. For example, using the diagram below, an eastbound signal at turnout A would show yellow if both turnouts were aligned, block B was clear, and Block C was occupied with an eastbound train. However the same signal would show red under the same sensor conditions if the train in Block C was westbound. Therefore, you could have direction based logic for the signal to accurately show the proper aspect for all possible conditions. This is easily done in the properties.

If using version 5.8 or later, the logic is setup as follows using this example:

Under the Trigger tab, you select the conditions for each aspect, except the default, usually Red.

Next select from the list of elements on the left those elements that would cause a Green signal, in this case Block 2 and Block 3 Unoccupied & Turnouts A & B Closed.

Next for Yellow. Select an "OR" group. With it highlighted, add another Group below it. Under this "&" Group select Turnout A Clear "&" Turnout B Clear "&" Block 2 Clear "&" Block 3 Occupied.

Under that new Group select Turnout A Thrown. That completes the conditions for triggers.

You will notice that we didn't add any triggers for Red. The signal will then default to this if none of the other conditions apply.

This is a rather simple example. Your layout may have some more complicated situations. Just logically consider all the conditions that need to be true for each aspect of a signal and enter those. If you have a double headed signal, you would need to add two signals on your switchboard and enter the conditions for each one.

Normally, if the above track was a bi-directional mainline, you would have double headed signals facing the points of each turnout, plus a single head signal facing the frog on the mainline and the siding at each turnout, for a total of eight heads. That would take up two drivers of the SE8C. The logic gets a bit more complicated for bi-directional traffic, as direction of travel would come into play.

The time invested is well worth it if you want to have accurate working signals on your layout. As time went on, I found a need for more signals, particularly at an area where a double track mainline met the throat of a classification yard. There are six signals located there. As a result, the number of possible conditions was multiplied.