CBUS & MERG

MERG (Model Electronic Railway Group) is an international, UK based group promoting interest in the application of electronics & computers to all aspects of railway modelling (quoted from their Website).

That covers one of my railway modelling interests and the annual fee of £20.00 (+£5 joining fee) is reasonable and includes a quarterly journal and access to a vast amount of information including a forum where your questions can be answered.

If you are doubtful about the quality of the group, you can download from the website a FREE book written by MERG member Davy Dick, entitled “Electronics for Model Railways”. This is a very comprehensive and informative introduction to the subject and I would highly recommend it as a worthwhile read.

MERG offer a growing list of kits, including Train-on-Track indicators, Gas Lamp Twinklers, a Computer Control system, DCC and the new CBus Layout Control System are available to members and, on occasion, ‘bargain’ components of model railway relevance. There are also basic projects & kits called Pocket Money Projects and these would appeal to starters in the hobby and those less confident in “things electronic”.

CBUS:  This is a universal layout control system developed by MERG members. The designers describe it as “a system for comprehensive layout control based on a general purpose Layout Control Bus (LCB). 
So what are the functions of a layout control system. You can divide these into two basic categories:

  1. Control of devices (outputs)
  2. Detection of ‘states’ (inputs)

Examples of (1) are changing turnouts (points), signals, power to block sections, turntables, level crossing gates, layout lighting, setting routes, controlling the speed and direction of locomotives (by DCC or analogue DC) and any other electrical or electro-mechanical devices that may be on a layout.

Examples of (2) are control panel switches, block occupancy detectors, bar code or RFID readers, turnout direction sensors, turntable position and ‘RailCom’™ track detectors.”

The choice of CAN: The CAN bus (Controller Area Network) was developed by the Robert Bosch company in the 1980s for use in motor vehicles but has since been applied to many other types of machinery including aircraft and medical scanners to name just two”.
Davy Dick, in “Electronics for Model Railways” describes it like this: “Imagine building a new layout consisting of four boards. With CBUS all you need do is run
four wires the length of the layout – two for power and two for the control system. No matter how many switches, button, lights, points, track occupancy detectors, accessories, etc. you now add to the layout, you still only need those four wires. The accessoryconnections between boards are always just these four wires – not the scores of wires associated with conventional wiring.”

But what does it look like on my layout, Brolgan Road?

In order to find out I built a small test panel to check things out as shown below. In simple terms the process runs from RIGHT to LEFT

  • starting with the module called CANUSB4. It connects to a computer off to the right by means of a USB cable and to the CANBUS twisted pair (red/white)
  • then comes the board labelled CANACE3 (to the designers, these acronyms made sense, but they puzzled me!) which is a switch interface that can handle 128 toggle
    switches or 64 pairs of push buttons. The module talks to the CANBUS and tells other things, in this case specific Servos to do something eg. operate points.
  • the module at the left labelled CANSERVO8 (I can understand this one – it controls 8 servos!) listens on the CANBUS and when it gets a message relevant to the points it controls – it talks to the particular servo concerned, and alters its state (normal or reverse). The servos do the business.

It’s interesting to note that the previously mentioned 4 wires seems true here (2 for CANBUS and 2 for 12DC to power modules, servos, lighting etc). But what about the DCC bus? That’s another 2 and it’s very prudent to divide the layout into SUB buses for DCC.
For example, Brolgan Road has 4 sub buses – loco, yard, carriage works, main station area and a number of isolating areas controlled by microswitches to isolate the areas either side of the lifting entry flap. Then, of course the servos have to be connected to the CANSERVO by cables and so it goes on!
BUT – if you are methodical and use colour coding and write a master list, then wire neatly and use labels, all will be well.

The video above shows a test rig built on a board being used to move a servo, in this case to find its centre position. The test rig consists of two Pocket Money Projects (PMP). The one on the left is a “Servo Controller/Tester” and all it does is respond to the position of the control knob (operating a variable resistor). It allows me to make sure the servo arm is fitted in the correct position – giving equal movement each way.

The PMP on the right as called “Ezy Points” and you will see it working in the video below. It is connected to a turnout test bed so that I can test the movement of the point blades. The 3 BLUE objects on the circuit board are variable resistors (aka potentiometers aka “pots”) which adjust 3 things manually with a screwdriver: speed; movement Left; movement Right, so that you can make the poin blades “kiss” the stock rail.

These PMP projects are fully described in the free book “Electronics for Model Railways”

An earlier test rig (below) better shows the “pots” (blue) and the standard RC (radio control) cable – yellow, orange, brown. You can get these in various lengths from hobby shops dealing in RC aircraft. Or, you can buy them on eBay very cheaply. You can plug them together for longer runs.
If you had a tiny shelf layout with a couple of points, you could use a few “Ezy Points” to control them. OR – you could use the servo to activate any other moving thingy eg. a gate, a signal etc. anywhere on your layout. Of course then you haven’t got remote control of all aspects like you have with CANBUS (or DCC).

The servo cable would normally come out the bottom of the layout.
Here is a close-up of the CANACE3 printed circuit board (PCB). You can buy the complete kit from MERG or just the PCB as I do and source the parts locally.
The soldering is not difficult but it requires practice. I will try to develop a VIDEO showing the process.
This is a close-up of the CANSERVO8 and this is a beautifully designed PCB of a more modern style. This board can control 8 servos and 2 are plugged in at the top. The long device in the centre with lots of legs is an IC and it can be purchased pre-programmed. It has all the “smart stuff” that responds to signals on the CANBUS and then bosses the servos around!

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Rick Fletcher

Born in the steam era and developed an interest in railways when given a clockwork Hornby "set". Surrounded by steam when travelling to school (by train of course) and holidays were always by steam train as we had no car. How lucky was I?

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