I’ve been working on this Xbee DCC thing for quite some time now and have finally finished it off. Or more like, I’ve finally gotten to the point where I think I could ‘release’ the code and the hardware. I have created a version 2.0 release branch for the code and have most of the hardware in a PCB state so it’s getting pretty mature. And more importantly, it works pretty darn good now!

The basic problem I’m trying to solve is how to control my trains, both electric and live steam, with one network. This network would also control pretty much everything else- turnouts, lights in buildings, signals, whatever. Everything on the network- trains, towns, turnouts, signals, would be capable of talking to everyone else, in real time. This would then allow you to tap into the network with a standard interface to leverage whatever application you want on top of it.

This is the reason I went with the Xbee. Unlike simple R/C or even Bluetooth, the Xbee (and I am speaking specifically about the Series 1 Xbee, NOT the Pro Zigbee) is a low level point to multi-point network. It runs at 250Kbps and has a range outside of about 100 meters or 300 feet. Every node on the network has a 16 bit address and can talk or respond to any other node.

One thing that took quite a bit of time to develop and test was the DCC output. The widget generates 128 step DCC throttle messages and DCC Function Messages F0-F12. It’s a bit basic, you have to program your DCC decoder with an external DCC unit and (for now anyhow) you only get those specific DCC transaction but as you can see from the video, that gives you lights, sounds and throttle.

I also completely redesigned the Master side code as well. It’s now far more generic in terms of messages. So I designed a new hand-held controller for it to reside in:


Hand Held Controller 2.0


Here is a basic diagram of what is going on in the U25B in the video. These are the components and control and power flows. Red is power, orange is logic, blue is DCC. Also, it’s not on the diagram, but the economi is controlling the lights and the Widget is driving 2 servos to automate each coupler. The ‘other I/O’ is also hooked up, a current sensor monitors the amps flowing to the trucks and there is also a photo detector that gives a pulse on every wheel revolution (for speed and distance). (The software is not currently looking at these however)


Basic Control Diagram


All of the components in the client are now on PCBs, no more proto or perf boards:


Nano Widget



Micro Widget



DCC Output



8Amp DPDT Relay






A couple of pictures of my latest iteration of wireless DCC and train control. This one has been refactored a couple of times and I now have a nice compact executable that takes throttle and function commands from any controller (in this case, my new hand held design) and converts them to both servo pulses (for the motor controller) and DCC output commands to control the lights and sounds. The speaker is a 2 inch full range with a passive radiator, sounds nice and full. The lights are all surface mount LEDs driven by CL2Ns. I also have servos on the couplers, they are tied to the F6 and F7 functions on the handheld.

Here are the basic components that go into the locomotive:


Everything is now driven by a simple command structure- throttle commands and function commands. The throttle controls the servo 0 spot, I’m using a 20A ESC to drive the motors in the U25B. The throttle commands are also used to drive the DCC decoder for the engine sounds. Since this is an HO Economi decoder, it doesn’t have the current output directly. But it does have great sound and I also drive the lights with it.

Why Xbee everyone asks? Because this is true networking. Everyone is on the same network and can speak or be spoken too. True point to multipoint. This opens up all sorts of possibilities for automation, signals, detection blocks and computer control. Something Bluetooth cant’ do. It’s also ‘industrial strength’ in that Digi has been making Xbee modules for many years now. They are FCC approved out of the box and



In addition to my own control system using Xbees, I also play around with standard radio control. I have one of the Hobby King systems shown above, I think it was like $25 for the TX and RX pair. In the second picture I’ve taken the TX out of the shell and replaced the joy sticks with pots. I’ve mounted it on a board so I can get to it’s innards.

Anyhow, what I’ve done is leverage my R/C signal software and my DCC generation software into one widget. I continuously sample the servo pulse coming out of the R/C RX and then translate that into DCC messages. In this case, throttle messages, although they could be anything.


It all fits into an 8 pin Attiny85, then feeds into my other new widget, the DCC output board.


With this board, one side goes to the battery connection, the other is the output. You can see the small R/C type connector which carries the signal from the Attiny to the board. The DCC output of this board then directly feeds the sound decoder.



Finally, here is a video showing it in action. You can hear the notches of the sound decoder increase as the output pot is twisted and the servo pulse width increases-


Above is the basic install I do on all my locomotives. The green RX box can be a regular R/C RX or it can be my Xbee Control Board. Same basic wiring.


Latest incarnation of the Phone Throttle Contraption. The phone communicates with the Xbee Controller via bluetooth, a custom app runs on the phone. This is based on previous experiments with an android tablet, you can read about that here- Android, Bluetooth and Xbee

I’m trying to emulate a generic sort of DCC throttle ‘feel’ with this. I have all of the base code written and tested, it’s just a matter of pulling all the parts together. Slowly I’m getting everything working.


Yet another project in the works. This one is intended to leverage my DCC circuit boards into a interrupt driven DCC I/O system for the Arduino Pro Mini. I actually have all of the software done and tested for both the input and output of DCC signals on my Attiny1634 board but I’ve never actually used a real ‘Arduino’. I’ve always built my own boards so this is a learning experience. I’m probably not going to make it compatible with the larger ‘Arduino’ universe, I’ll just optimize it for the Pro Mini. Anyhow, this project is actually number two on the list, the refurbish of my U25B locomotive is first so I can polish off the main widget code base.


Yes, I know this is a little weird but I want a knob AND a nice user interface (ala smartphone) to run my trains so I am working on this design. The Knob and underlying circuitry communicate directly with the 802.15.4 network. The phone is just there for the user interface and graphics. Bluetooth is used to communicate between knob/wireless controller and the phone. A custom app runs on the phone. I have the infrastructure working for this, its just a matter of smushing all the components into this small space and refactoring the software a bit. Both the case and the face plate for this were cut on my Probotix X90 3D router.


Today I got my order of printed circuit boards from Bay Area Circuits. I promptly populated them with components and powered them all up to see how they would do. Everything works! Very nice! Next step is to install these into one of my locomotives and replace all the breadboards with something clean and production quality.

Pictured, in order, is the 8Amp DPDT relay module, it’s used to reverse the direction of the locomotive. It can be triggered either with a logic one or zero, say from an Ardunio, or from an R/C signal via your generic radio control system. (The logic version is shown, the R/C version has an additional chip on the board, you can see the outline).

Second is the DCC output module. It is designed to be driven with a logic signal from a micro-controller such as the Ardunio. Logic input in, attach your choice of battery (or other) power to the input terminals and it provides up to 3Amps of DCC encoded power on the outputs.

Below that is the DCC input module, connect this to any DCC device like the MRC Prodigy or NCE DCC units and it converts the high voltage DCC signal down to what a micro-controller or Ardunio needs.

The last one is my Control Widget Node. This device is a micro controller wired to an industrial strength Xbee Series 1 802.15.4 Wireless Network Module. I use this for both my Control and Slave nodes. It allows high speed data delivered in an organized network infrastructure with a range of about 300 ft. I send both proprietary packets and DCC messages over this in real time. This is the latest PCB design.


I’ve been doing quite a bit of PCB design these days, here is a version of my controller board, the ‘microwidget’. It’s quite compact. I have not had any made yet but I thought it came out really sort of, well, neat. Like art kinda.

All total I have about five or six small circuits for doing control networks- specifically for large scale model trains. DCC input and output, servo control, DC brushed motor control, reversing relays- all via Industrial strength Xbee Network wireless.

I’m also thinking of making an apt-get debian package to install JMRI on a RPi 2 and gitlab for my code. Hmm.

I think I need a Kickstarter 🙂



Here are the final two prototypes. The master obviously connects to the Prodigy Express and sports a long range antenna for max transmission power. What I’m thinking here is this is the module that will be connected to my RPi 2 which I am planning on running JMRI on. The Pi 2 will also have a long range wifi antenna on it so I can use it to source web pages to my phone and tablet. My standard handheld design is what I actually use to drive my trains with.

The second pic is the client. This one is fairly comprehensive and has quite a few parts but I use it as my standard prototype rig. In addition to the control board, it also has an (expensive) Pololu 18v7 motor controller and a current sensor. The DCC output stage is the board with the large chip beside the speaker. All it is used for in this incarnation is to drive the Econami Diesel DCC decoder which powers the speaker on the right.

Here are all the parts labeled, you can click on the picture for a larger version-