DC/DCC Control Box

One of my favorite activities is DCC decoder installation. It is essential that a locomotive that is being converted from DC to DCC runs well. DCC will not solve any mechanical problems, it can only mask them or in some cases, make them more evident. Therefore, DC testing is essential. I have a complete test track with “rollers” to test and diagnose DC locomotives but sometimes you need to run a loco round a track to see what the problems are and help to troubleshoot them. So, I wanted the option of both DC and DCC for my layout and a method to easily switch between the two. This is my solution.

The box is built from 3/16″ plywood. The bottom is 1/2″ ply and the sides are glued and nailed on. I stained them with some Minwax stain. The top is 3/16″ ply as well but I painted it black. I sealed the paint with clear satin and used individual letter decals to letter it.

The pic shows the layout. On the left is the DC control section. Can you guess where the knob and track power indicator comes from? Yes, an old Troller pack. I had one that had failed and used the internals to make a DC controller. These Troller packs were notorious for failure, which is too bad because otherwise, were a good unit. This one had the power transistor fail from improper heat sinking. A replacement was cheap and I actually found one in my electronics scrap box.

On the right is the DCC area, I’ll go into more detail on that, but for now what you see is a push button and LED indicator for the Raspberry Pi that runs JMRI. The Pi is an excellent single board computer. It can run without a monitor, keyboard and mouse connected but without a power switch, the only option for power down is pulling the power cord and that can cause issues. There are all kinds of methods of powering down and with a single push button and a little code, the button safely shuts down the Pi. As you can see, I’ve gone with a retro look. I find that pleasing.

Let’s look at the DC controller. The photo shows the wiring. It’s quite a simple throttle. I used the Troller printed circuit board. The board includes a bridge rectifier for the AC transformer in the original but I have a DC power supply in the box that powers everything so I simply hooked the DC from that to the output of the rectifier. I didn’t like the slide switches of the Troller so used toggles. I especially didn’t like the momentary slide switch Troller used for the brake, the spring was very stiff. I substituted a push button for the brake. The transistor is mounted on a hefty heat sink to prevent future failure. The output goes to a DPDT center off Toggle connected to the tracks for selection between DC and DCC

The DCC section is a bit more complicated. I’ll walk you through it. The command station is a DCC++ DIY unit. Using an Arduino and a motor shield, the DCC signal is generated and can drive up to 2A. Well, in theory anyway. The unit would get very overheated at 2A. There are extensive details on DCC++ elsewhere on my site, just go to the home page and have a look. It’s an easy, inexpensive system with little to do and NO SOLDERING!

As it is, the DCC++ command station needs something to send DCC signals. For that, I use JMRI. JMRI is an open source project and many are familiar with it. A google search for JMRI will give you more information than you can imagine. I won’t go into that here. JMRI needs a computer to run on and that’s where the Raspberry Pi comes in. It is a credit card sized computer that runs a version of Linux. Steve Todd has created an image that can be uploaded to the Pi that has JMRI installed and configured. It is set up as a WiFi router that you can connect your cell phone or other device to control trains wirelessly using an App on your device. This connects to the DCC++ base station with a USB cable.

The power to the Pi is the recommended supply, so I needed a 120VAC source, I have accomplished that with a receptacle salvaged from a computer power supply. AC is switched with a toggle. The AC also powers the DC switching power supply.

The 2A capacity of the DCC++ base station is amplified to 5A with a booster. The booster I use is a MERG kit. Details of that are found on this site as well. The booster has an audible short warning that screams until it has detected a DCC signal, so to prevent that as the entire system powers up, I have included a relay to stop the booster from getting power until the DCC++ unit is up and sending a signal. I simply rectified the DCC signal and connected an automotive relay to control DC going to the booster.

Finally, I installed a fan to keep air flowing and prevent any heat build up in the box. Below are some detail pics. Please email me with any questions or comments. gregw66@gmail.com

Leave a Reply

Your email address will not be published. Required fields are marked *