Railroad Signals

Railroad signal

Setting up railroad signals for your layout is another fascinating aspect of using electronics and special wiring effects in model railroading. Imagine your train traveling from one town to another through freight yards and junctions with a series of signals automatically changing as your train goes along. If another train moves into the track ahead, the railroad signal will turn red and your train will stop until the track ahead is clear, after which the signal turns back to green and your train can then proceed. Sounds neat, doesn’t it?

What do the railroad signals mean?

Some of the prototypical railroad signal systems are complicated and were designed specifically for the individual railroads, each system being a little different. Basically, for our purposes and considering the signals that are commercially available, we will use the “standard” designations as follows:

Red – the block of track ahead is occupied. Stop and wait till the light changes to yellow or green indicating that the track ahead is clear.

Yellow – Slow down. The block ahead of this next one is red, or occupied.

Green – Both this next block and the one after that are unoccupied, and it’s okay to proceed.

Check out this page for information on prototypical railroad signal systems and terms.

For more detail on how to read railroad signals for CSX...

To get started without too much effort and expense, while you’re building the rest of your layout, you may want to just use the manually operated signals made by Model Power, available at many hobby shops. A switch comes with each signal that allows you to manually change the light from red to yellow to green. Evemodel also makes signals that are easy to set up for manual operation although you have to add your own switches. See the page on Wiring Model Railroad Signals.

Sooner or later however, you will want to invest in the kind of system described above that operates automatically…

Train Detection Devices and Sensors

First, you will need some type of train detection device, to “tell” the signals when a train is approaching. There are 2 ways to do this:

Track circuit detector– This requires block wiring and detects the presence of a train on the block by the change in current that occurs when the train rolls onto that block. You will need track circuit current detector boards – one for each block – such as the one made by Dallee Electronics, Inc. called the TRAK-DT. This detector recognizes the change in current and activates a relay switch that changes the signal, turns on a light on the control panel, activates a crossing gate if one is present, or turns on or off a block of track, e.g., to start or stop a train.

Position sensor – detects the presence of the train as the train passes directly over the sensor. These can be optical sensors, magnetic reed switches or infrared light sensors. When a passing train activates any of these sensors, an impulse is sent to the circuit board, which changes a train signal and/or a crossing gate, and could potentially turn on or off a section of isolated track using a relay switch, depending on the type of sensor used.

More on position sensors…

Optical position sensors (photocells) are small devices made by Circuitron and Logic Rail that you can place between the track ties. When a train passes over, the device detects a change in the light and sends an electronic message to a circuit board, which then operates the signal or crossing gate.

Magnetic reed switches are also placed between the track ties, and when a train with a magnet on the bottom passes over the switch, the magnet causes the contacts in the switch to come together, again sending an impulse to the circuit board to change the train signal. A second reed switch set up in the same location could turn power on or off to a section of isolated track that would stop a train from entering a restricted area - an area occupied by another train.

Infrared sensors are phototransistors, which are set up across the tracks from an infrared LED light. When a train comes along and blocks the infrared beam, a message is sent to the circuit board to change the signal lights and/or crossing gate. These work when the overhead lights are on or off, whereas the optical position sensors only work when the lights are on.

The IRDOT infrared detector by Micro-Mark is a little more sophisticated. It is mounted under the layout and shines an infrared beam through a hole drilled in the layout surface. When a train passes by, the light beam is interrupted, which sends an impulse to a circuit board that can change the signal lights, but can also activate sound effects, animation devices, other lights, or send an impulse to a relay switch that could turn off power to a block of track.

Another infrared detection unit made by ITTC can also activate other animations or lights. The difference is that this one has a timer that can be set to delay the onset of when these items are activated.

You may also wish to check the website at Azatrax, which contains clear and detailed explanations on how to install infrared train detectors.

Railroad signal. These are an important part of a good model railroad layout.

Setting Up a Simple System of Operating Model Railroad Signals

First you have to decide whether you want to use track circuit detection or position sensor detection. Position sensor detection is a little easier to set up and is great for smaller layouts. Also, you won’t have to block off sections of your track as you do with the track circuit detectors. If you’re already using block wiring for train control, then the difference in set up is not that significant.

One other thing to consider is that if you are using current (circuit) detection, the block will appear occupied whenever there is current being drawn on that block, either by a locomotive or by an insulated metal wheel set (on a rail car or caboose) containing a resistor between the 2 sides. If the power is not on to that block, or if the loco or other power-drawing car is not actually in that block, it won't be detected. So you could have one or more rail cars sitting in a block that won't be detected, and the signal to that block will remain green.

By the same token, in order for a position sensor to work properly, the train has to be located directly over the photosensor or within the beam of the IR detector. If the train is present in the area, but not covering the detector, then it won't be detected.

Let’s assume you have chosen to use position sensors. In that case, you may want to use Logic Rail’s Signal Animator for your circuit boards. If you had chosen track circuit detection, you would use Dallee’s TRAK-DT, most likely, although there are other types of circuit boards available; they don’t all work with both analog and DCC, however, as the Dallee does. You’ll have to be careful that you choose one that will work with your wiring system and power supply. The TRAK-DT requires its own regulated DC 12volt power source (made by Dallee) that can be connected to your fixed AC terminals of your transformer.

You will need a Signal Animator unit for each section of track that you wish to control with signal operation. Each unit comes with a photocell. This is adequate if you are only running your trains in one direction. However, if you want to run trains in both directions, you will probably want to have a signal on both ends of the “restricted area”, facing opposite directions, both of which could be controlled by the same circuit board since the light change will be the same on both railroad signals. In this case you will need to wire another photocell in series with the first photocell, but placed near the second signal. This way, if a train approaches the “restricted area” from either direction, it will pass over a photocell, activate the circuit board and change the lights on both signals to prevent the flow of any other traffic into that section of track.

Next, you will need to decide on whether to use 2-light or 3-light train signals, which are made by Tomar and other companies. The Signal Animator will work with either type.

You will also need 24-gauge wire to make the connections.

To install the system, you have to first determine where you want to place your signals, which will then help decide where to put the photocells. Basically, you will most likely want to place your signals wherever there is a place where 2 or more trains could potentially run into each other if there are no railroad signals to control them - next to busy turnouts for example, passing sidings, junctions, or exits from yards or spurs onto a mainline.

The wiring instructions are included with the circuit board and are fairly straightforward. Each photocell has 2 wires: one wire from the photocell goes to the place marked PC on the circuit board and other wire goes to GND. Wires from the terminals marked Y,R and G go to the yellow, red and green lights on the signals respectively. A wire from the +5V terminal goes to the signal. If the signal lights are LEDs, they will each need a 150 ohm resistor soldered to the anode (positive, or long wire) of the LED. Further instructions can be found on the Logic Rail website at www.logicrailtech.com.

The Logic Rail Signal Animator circuit boards are set up so that when a train covers a sensor, the signal turns red to prevent other traffic from entering. Then, after a train rolls beyond the photocell and uncovers it, there will be a 10 or 30 second delay before the signal changes back to yellow and then green (or just green if you’re using the 2-light signals) to allow the train to clear the area before the next train can move in.

The Atlas 21st Century Signal System (www.atlasrr.com) is also available for N, HO, and O scales and is able to provide very realistic prototypical signal operation for your layout. The circuit board is capable of simple stand-alone signal operation, integrated operation, approach-only operation, or complex signaling functions.

This looks pretty realistic and fairly impressive to have railroad signals changing in synchrony as your train travels around the layout, even more so if crossing gates are operated automatically and if other lights or sounds or animated devices go on and off as your train passes.

This is cool stuff!!

Railroad signalsTrain Yard with Various types of Railroad Signals


A Beginner's Guide to Creative Effects for your Model Railroad

www.customsignals.com - Signals in N, HO and O scales. Advanced signaling for all scales using the Atlas 21st Century System and the Custom Signals Modular Signal System.

Train rules, block signal rules, interlocking rules, signal indications and aspects, general regulations

www.oaktreesystems.com - Manufacturer of electronics and software for signals systems and layout control.

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