JMRI Hardware Guide: NAC Services RPS

Please note that JMRI's RPS support is being rapidly improved. This page refers to most recent JMRI test version. If you're using an RPS system, you should update to new test versions as they are announced.

The NAC Services RPS System allows you to locate the exact position of locomotives and other rolling stock that have been equipped with transmitter decoders. The system makes up to 10 measurements per second and each reading is accurate to much better than an inch, which makes many imaginative uses possible.

Supported DCC Systems

The RPS system works in conjunction which your DCC system to control when the RPS transmitters are activated. You therefore need a working connection between your DCC system and JMRI to use RPS.

At the present time, RPS is supported with DCC systems from:

Digitrax
Lenz
NCE

Others may work, and we're interested in making them work, but they haven't been tested in combination with RPS yet.

System Setup

First, get your DCC system working and connected to JMRI. As a good test of the connection, you should be able to turn your layout power on and off from the JMRI Power Control in the Tools menu.

Next set up the RPS hardware following the RPS instructions. You may want to only install a few (but a minimum of three) receivers while you're first getting the system working.

Next, connect your computer to the RPS using either a USB connection or an RS232 cable from a serial port. If you use an RS232 cable, not that it should be a "straight-through" or "modem" cable, not a "crossover" or "null-modem" cable.

Next, configure the JMRI program.

Start your JMRI-based program (DecoderPro, PanelPro, etc).
Go to the preferences panel of the program. This opens automatically the first time a program is run, or you can select it from the "Edit" menu.
Your DCC connection should already be configured in the top section, see above.
Click "Show advanced preferences" to open a new part of the preferences window.
Select "RPS Base Station" from the "Aux connection 2" selection box.
In the associated port selection box, pick the name of the serial port that you have connected to the RPS system.
The baud rate will show a fixed value of 115200 baud.
As a temporary measure during development of the system, there's a "Protocol" option to select. The valid choices are "Version 1" and "Version 2"; your hardware determines which to use. This will eventually be automated.
Click "Save". You'll be asked if it's OK for the program to quit, click "Yes".
Restart the program. It should come up saying it's connected to your DCC system, and just below that saying it's connected to the RPS Base Station on the proper port.
Next, you have to enter alignment information. From the RPS menu, select "Receiver Control". This will open a new window.
In the middle of that window, enter the number of highest-numbered receiver you've got. Press the "Set" button next to that field.
In the table at the top, enter the X, Y and Z position of each of your receivers. If you don't have a receiver with a particular number, leave that row blank. For now, just enter approximate values.
Click the "Set Defaults" button to save these positions as default values. They'll appear again when you next start the program.

At this point, your RPS system is ready to go.

To have your RPS system start measuring positions, you have to tell it to poll the locomotives in which you've installed RPS transmitters. To do this:

Open the "Polling Control" from the RPS menu
You should see all of the locomotives in your roster
Check the box under "Poll" for each locomotive in which a RPS transmitted is installed
Check the "poll" box to start making measurements
Click "Store New Default Values" to store these settings so they'll be used the next time you start the program.

To see that the system is working, open the "Debugging Display" from the RPS menu. You should see time readings coming in and being converted to positions. You can also check the communications with the unit by opening the "RPS Monitor" from the RPS menu.

RPS Tools

JMRI provides a number of tools in the RPS menu for working with the RPS system:

Receiver Control: This is where you enter position information about your receiver positions, etc.
Polling Control: This is where you tell JMRI which locomotives have RPS transmitters, and how often you want JMRI to poll them
Debug Display: This shows you the readings and measurements as the system makes them
Tracking Display: This shows the points as they are measured on a graphical display.
Sound Speed Control: This lets you see and set the speed of sound used by the RPS system, and can set it automatically in certain cases.

You can also display RPS information on PanelPro control panels using an "RPS Icon".

RPS information may be used to detect occupancy using JMRI RPS Sensors.

For More Information

There's more information available on the NAC Services Web Site.