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Nifty Trackside Devices from TDP

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Don Fiehmann has reviewed some of the nifty trackside devices now offered by TDP Associates: FlashMaster™, ServoMaster™, ABSMaster™, and TrainSpeed™.

TPD and Associates started this line of track-side devices with a speedometer that would read out the speed of a train in miles per hour or kilometers per hour. They have added new products to the line for control of crossing gates, grade crossing lights and track signals. These track-side devices add action to a layout as a train rolls over the tracks. The devices are activated by using photo cells that sense the presents of the train as a car or locomotive casts it’s shadow on the photocell. This method of train detection relies on room lighting. TDP has now added to their line an alternate way of detection by using IR (infrared) detectors. The IR detectors have there own light source and use reflected light to detect the presents of a train. The IR detectors solve the problem of insufficient room light or where the room lighting is dimmed for “night” operation. Both the IR and photo cell method of train detection have the advantage of not being connected to track power. This allows the sensors to be placed independently of the track blocks. Using detection that is separate from the rails uses photo cells or IR sensors between the rails, they will work in any scale. The circuits are entirely separate from the rails. This means they will work with battery power, DC or DCC controlled trains.

Photo cell shown

Photo cell shown

Each of these products comes with a circuit board to control the track-side device. The inputs to the circuit boards is normally the photo cells or IR sensors. Other detection units, like detectors that monitor track current can also be connected as inputs to the circuit boards. Most of these types of detectors are used to operate track signals, nice for railroad signals, but the ends of these blocks do not normally fall where you have a grade crossing. The photo cells and IR sensors can be placed anywhere on the rails and do not have to line up with the ends of other blocks. This gives you the freedom to place sensors in the most logical locations and not be confined to the track block ends. I have two location on my layout where the road crosses the rails. The roads maybe close to my detected section used for signaling, but still not in the right locations to correctly operate the grade crossing gates and signals. Using the photo cells in the right place solves this problem.

Comes with control board and attachment cables FlashMaster for grade crossings

Left: Comes with control board and attachment cables.
Right: FlashMaster for grade crossings.

Each of the track-side devices comes with a circuit board that connects to the photo cells, IR sensors or other detectors. These boards then drive the output devices. The circuit boards are programed either with jumpers, push-buttons or a pot. The input voltage can be from 9 to 16 volts AC or DC.

Both the FlashMaster and the ServoMaster have a feature that they will time out in 2 minutes if the circuit fails to get a signal to stop. If someone accidently casts a shadow in one of the cell and trips the circuit, it will only stay on for two minutes before it times out.

The products by TDP include the following:


Controls two grade crossing signals on a single track line. Works in either direction. The crossing signals can come from companies like NJ International or Tomar.An optional sound module (from Innovative Train Technology) can be added to provide the bell sound at the crossing.

Tomar crossing signals with the bell casting on top worked well with the FlashMaster.

The detection for the FlashMaster uses three photo cells that are pre-wired on a long cable that plugs into the circuit board. Two “start” photo cells are used at a distance from the crossing to start the flashing lights and the third one is place at the grade crossing. This third photo cell is used as a hold indication until the train has passed. There is a couple of seconds of delay before the signals stop to be sure the train has passed and it is not just the light from the gap between cars. If you have more than one track, there is an Expansion Kit that will increase the number of tracks controlling the signal circuits. Each track can have two way traffic.

The FlashMaster was installed on a section of single track mainline. The sensors were placed about four feet away from the grade crossing in each direction. Once the signals were installed they were tested and worked OK with the room lighting. The alternating red LEDs are an attention getter. Neat to watch the lights as the train goes by, but you got the feeling that something was missing. It was the ding-ding-ding of the bell at the crossing. One of the outputs from the control board is a line to activate a sound module. A HQ300 Bell Sound from ITT was added and completed the scene.

Once installed the FashMaster would trigger falsely occasionally. This problem was solved by rasing one of the photo cell sightly to catch more light. No false triggering since the photo cell was moved.

If the room lights are turned off before the layout power is turned off, the bell will start to sound as a reminder to turn off the layout. Neat unexpected feature.


Operates like the FlashMaster. It not only controls the crossing lights and adds controls for two crossing gate arms. It can be used on either a single track or a two direction mainline. This has the same type outputs to control lights on a crossing signal, plus two servos that can operate crossing gates. These same servos can also be used to control semaphore signals. The circuit board has the program setup to make the servos start and stop the crossing gate arms at a controlled position. You can also control the speed of the servos that move the crossing gate arms. These same controls can also be used to control the speed and positions of the arm on a semaphore. There is also an output to operate the bell sound module.

ServoMaster Parts

Left: The SevoMaster will control two crossing gates. An expansion kit will allow control of up to four bidirectional tracks.
Right: ServoMaster Parts.

When used to control a crossing gate the logic operates the crossing gates like the prototype. It has the same photo cells arrangement that starts the signal working and then holds the arm down until either the train clears the hold photo cell at the crossing or comes to the two minute time out. Someone just told me that he was stopped by a crossing gate and did not see any train in either direction. After 2 minutes the gates went up and there never was a train. So I guess the time out conforms to the prototype also.

The crossing gate signal mounts like the other signal with the added control wire to operate the crossing gate. This wire is attached to the servo. The servo comes with a couple of different “arms” to choose from to match up with the device to be controlled. The instruction show the servo mounted on a piece of wood under the layout. The area where the servos need to be install was tight. I used a couple of metal corner brackets to hold the servos in place. Only a small hole was needed for the signal and another for the crossing gate control rod.

The servo is mounted under the table and connected to the crossing gate with a thin piece of wire that connects to the gate’s arm. This is an earlier version of the ServoMaster that needed a micro switch to trigger the bell sound module. This is not needed with the latest release that has an output from the circuit board for the bell sound.

The two boxes that Jim Betz built make it easy to remove the signal when working on the track.

In a second installation Jim Betz mounted the crossing gates in a box like structure made out of styrene. The servo was installed as part of an assembly with the signal. This allowed the adjustments of the crossing arm to be done before the signals were installed on the layout. The outside box was installed on the layout. The inside box could then be dropped in the outside box. The big advantage is the inside box can be slid out when cleaning the track and prevent damage to the signal. The hole in the side of the inside box lets you adjust the crossing gates. Connectors at the end of the wires allow the signal and box to be disconnected and completely remove from the layout.

Expansion Kit

Allows the number of tracks to be increased from one up to four. The expanded tracks can have rail traffic in either direction. Each added track requires an expansion kit. Installation of the expansion kit requires that the input logic of the ServoMaster be inverted. It very simple matter of setting the input level when programming the ServoMaster.

Expansion Kit has circuit board and cables.

As suggested in the instructions we install the ServoMaster and tested the photo cells on each of the tracks separately. Once both tested OK, we installed the Expansion Kit and reprogrammed the ServoMaster for the Expansion Kit. This was easy to do following the instructions.


Like to now how fast your train is running, or need to match speeds on locomotives? The answer is the TrainSpeed with a readout that shows the speed of a train or engine. The TrainSpeed is comes in two models. The TrainSpeed monitors one location on the layout and comes with a 3 digit display for speeds from 1 to 999. The TrainSpeed4 can monitor 4 locations on your layout and comes with a 4 digit display. The added digit is used to show which of the four locations trigger the speed display.

Jim Betz did his styrene magic to produce a panel to mount the TrainSpeed. The display is large enough to been seen at a distance.

The speed readout is determined by the time between a train tripping the first photo cell and then the second photo cell. The distance between the photo cells changes depending on the scale and if you want the readout in MPH or KPH. The distance can also be from 1/50 to 1/400 of a mile or kilometer by setting jumper on the circuit board. A chart in the instruction manual lists the distances for different scales and parts of a mile or kilometer. There is also information on computing a distance for a scale that is not shown. For HO, 7.283 inches is used for 1/100 of a mile.

When power is applied to the TrainSpeed it does a startup diagnostic test to determine if the photo cell are Ok. When a train passes over one of the photo cells the display blanks out until the train passes over the other photo cell, then the speed is displayed.

When we installed the TrainSpeed we got a message that the photo cells were OK, but we could not get it to trigger for speed display. It turned out that even when the photo cell were covered, there was enough light to prevent the circuits from triggering. By moving the photo cell a little deeper into the hole to restrict some of the light, bingo, it worked fine.


This system can control up to four signals as either 2 or 3 color signals. It can drive either lamps or LEDs. The ABSMaster provides prototypical ABS signal control for four blocks. It works with all LED based signals, two light, three light, searchlight and position light. The ABSMaster uses the same type of photo cells to determine the blocks as used by their other devices. The IR sensors are also available where you may need to have limited lighting.

The ABSMaster comes with all the cables and a control board. You supply the signals of your choice.

This signal system will work with either a DC or DCC layout . With DC the blocks were shorter, with DCC we tend to have longer blocks (power subdistricts). By having the photo cell determine blocks, they can be placed any convenient location where you need a signal and not limited to electrical blocks. Block lengths can be variable. On a two track section of my that is on a grade and the up hill, where speed are slower has more signals than the down hill track where speed is faster. The flexibility of placing blocks independently of electrical blocks allows the signals to be placed where they are the most visible to crew and visitors.


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