Category Archives: Electronics

A day of modelling progress

Thanks to Mark Tatlow for hosting today, and to Oly & Chris for great company. I think all four of us made progress on various projects. Mark was making holes in the side of a nice looking Gresley Buffet, and had made them disappear again by the end of the day.

My own projects were to try and complete the build of the MERG DCC system for SLAG’s Bankside project. I had to cut a new support for one of the PCBs and jigsaw it all into the case. I succeeded at the first task! Re-assembling the boards (it is a bit of a jigsaw puzzle), I discovered one of the internal connections wasn’t mating correctly, so that will need replacing in another session.

Here’s one of the boards, captured to record which colours I’m using for connections (note to self: green: 0vDC, Blue, +5vDC):

PCB and wiring harness

This one replaces the buzzers the system uses by default to tell you when there is a short or other fault. By translating that information onto CBUS, we’ll be able to have buzzers or LEDs at any control station. Hopefully those will be more useful in noisy exhibition halls.

For the afternoon, I dusted down the Tornado chassis I’ve been looking at for a while, and assembled two more links for the Walschaerts valve gear.

A MERG DCC System

Over the last couple of posts, I’ve been building up to completion of a DCC system assembled from MERG kits.

Last week, I had the pleasure of taking it to the South London Group’s clubroom, to trial it with our new layout. It worked!

merg-dcc

What we can see here is (starting at the loco on rollers), a class 20 on the ‘layout’ output of the system. To the right is the programming track, and alongside that we can see the command station. This provides the DCC signal for the layout, and a direct connection to the programming track. The command station has no directly attached controls, and cabs (one is at the bottom) are connected over CBUS. Since CBUS is a publicly documented standard, I intend to develop custom handsets over time. I’m intrigued if exhibition layouts will be easier to use if the controls are designed with the operation of the particular layout in mind.

To the right of the picture, the top board is a 5A DCC booster, which provides the actual layout power and DCC signal broadcast. Below it is a USB to CBUS connection. Not directly needed for the system to function, it will facilitate future firmware upgrades to the command station and handset, and permit me to prototype the custom handsets on a PC before committing them to electronics.

Surface Mount Practice

MERG provide a couple of kits intended to be used as practice for surface mount soldering. This is my second go at this, and the first working attempt:



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My first attempt failed because I wasn’t familiar with how pin 1 on the IC was identified. I now know it is the chamfer along one side. My first attempt had the IC the other way round, and rapidly burned out without flashing the LEDs, as this circuit is designed to do. For a £3.60 kit, it seemed like a good value way to learn the lesson. The instructions did explain all this, but somehow it still didn’t sink in without the practical lesson!

A MERG DCC Controller

I want to explore the options that present themselves when lots of my layout wiring is digital. Step one is to drive trains via a PC.

MERG have a set of kits for a system designed around the CAN bus. This is the ‘DCC command station’ and a USB to CAN interface module. The loco lurking in the background moved under the power of this system earlier tonight.



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Now I want to build a handset so that the computer is optional. The kit MERG have will mean I need to get the knack of surface mount soldering by hand.

This also means JMRI is installed on my PC again. It’s nice to see how much that has updated recently!