The build of the fitted iron mink, featured in my last post, is progressing rather slowly - a combination work projects, being away for a week or so, and the current heat. The room that serves as both my home office and modelling room is in our loft conversion, and gets very hot in the current kind of weather, which rather puts me off doing anything. So, to fill the gap before the mink is finished so I can write part 2 of that post, I thought I would share some pictures and notes on the DCC control system I built a little while ago.

The system uses MERG modules in a custom-built case. MERG, for those not familiar, is the Model Electronics Railway Group, and joining MERG gives access to the wide range of kits for electronics modules the group produces. In my case, I chose:

• CANCMD2 - the heart of the system. This module takes commands from any controllers attached to the CBUS bus, and outputs DCC commands to the track.
• CANCAB2P - a hand-held controller, that connects to the CBUS
• CANUSB4 - an interface that connects the system to a computer (Mac or PC) so it can be controlled by software such as JMRI.

Here is an overview of the system - from left to right: the power supply (also provided by MERG); the CANCAB controller; the cast metal case with the other modules in:

Inside the case:

Under all those wires and the two switches are:

• Top left - the USB module
• Top right - the CANCMD2 module
• Bottom left, in the shadows - the small, separate PCB with the socket where the CANCAB controller plugs in.

Also visible is the buzzer (the white thing attached to the side of the box at the top) which signals fault conditions.

Connections are at the end of the box:

One of the two switches changes the command module from programming mode to 'track' or 'layout' mode. The module outputs a maximum of 1 amp, so enough for a small layout or for use with low-power locos. A booster module can be added if more current is required. The other switch terminates the CBUS - the bus needs to have terminating resistors at each end, but not anywhere else. I have included a socket so additional CBUS modules can be added, in which case the termination must be turned off, and a terminating resistor provided at the end of the string of additional modules.

I decided to recess the switches, partly to prevent them getting damaged, but mainly so they wouldn't get changed accidentally:

The kit for the CANCMD module is just for the PCB and electronics, leaving the user to provide a case. The CANCAB controller kit, though, comes with the case and labelled front panel - everything you see here:

The meters are a bit of frivolity on my part - they aren't strictly necessary, and if you want them, a module with digital meters can be had more cheaply, and which probably gives greater accuracy. What can I say - I like old-school dial meters, and these retro-style units make me smile.

The voltage meter reads the track voltage. It is a DC meter, so a rectifier module converts the AC track power / DCC signals to DC - you can just see it glued to the inside of the lid between the two meters:

The current meter is also DC, and reads the current as it comes into the unit, from the power supply. This means it reads the total system current draw, not just that of the track.

I chose the cast metal case because I wanted something that would act as a heat sink for the CANCMD module, and I find these cast alloy types easier to drill and work than steel cases.

The MERG kits come with excellent, detailed instructions, and provide a cost-effective route to a DCC system, as long as you are happy with electronics soldering. Mostly this is straightforward, but the CANCAB module has some quite small, fiddly bits to do.

I haven't worked out the details yet, but I think it should be quite easy to adapt a CANCAB module to work with other hardware for the speed knob and buttons, to build it into a more conventional control panel. At present, though, I don't have a layout, so this set-up means I can run a DCC loco on a short test track, and it will also serve for a small layout when the time comes.

Nick.