Platform 1

But look what you've learnt on the journey! Onward and upward

Mmm, yes, Anneka... But this is a great post because it shows modelling as it happens and that people's efforts don't always look like Liverpool Lime Street or Manchester Central (which are fantastic but can be demotivating). Most of my efforts look like your Goods Shed Mark 1, so full marks for telling it like it is!

The amended objective was to produce a simpler, no-frills DC controller that would meet the original 'anytime anywhere' requirement, working with either a battery, AC or DC power. Circuit Design Starting with the emf-sensing feedback circuit used in Part 1, I removed the integrator and schmitt trigger U1 leaving just U1b as a simple non-inverting amplifier. The output driver Q1 - a cheaper and more easily obtainable BD243C - is included in the gain loop to ensure good output voltage regulation. Resistor values were re-calculated so that RV1 would provide a full 12v range at the output. D3 is retained to clamp any back-emf or spikes from the track and/or loco motor. D2 protects the op amp from reverse voltages at power off by discharging C3 via the supply rail. I also took the opportunity to add a current limiter to protect Q1 from track short-circuits - more a case of 'when' than 'if'. R7 and Q2 work to 'steal' current from Q1 when more than about 500mA flows through R7 - adjust R7 for different limit-current values. Two 3R3 0.25W resistors in parallel worked well in my case - my N locos draw up to about 250mA. Note that Q1 will need a heat sink for higher current motors; use of a metal box might be the best approach. The unused half of the op amp is wired as a unity gain stage (pins 6 & 7 linked) with its input (pin 5) grounded so as to minimise stray pickup and noise. To aid testing, typical voltages are shown in green. Construction The circuit was built using the same approach as in Part 1 - perforated stripboard - and with the same size plastic box 80x60x40mm. The reduced component count meant an easier fit on the board, but my board layout shown below is rubbish - too many wire links. In case anyone else wants to build it, pinouts for active components are shown below. All wiring was again checked twice. Testing As this is plain old DC a voltmeter should suffice when checking - no wizzy pulses to worry about this time Power was first applied with no load. The output seemed to waggle happily up and down as RV1 was turned forward and back. With a loco on the track, smooth control was noted - very gratifying! As expected, creep control was not as good as the feedback controller. However, it was possible to move a loco very slowly with about 2.5v applied to clean track. One observation: "zero output" at the minimum setting of RV1 is actually 2mV. It may be just stray pickup in my test rig, and is unlikely to cause problems, but worth noting. Top speed using a 12v battery - giving about 10.5v to the track - was more than fast enough for realistic running, so maximum oomph will rarely be required when using a 13-15v power pack. Conclusion Sometimes simple (KISS) is best!

Thanks Mike - I've always dabbled in electronics since I built my first (valve) radio at 14. But the SMT stuff is too small for me now, so keep experimenting whilst the bits are still cheap and big enough to handle! There are lots of good tutorials on the interweb, so just dive in... Best wishes, Tony P.S.Your microscenes are fantastic!

Quite an achievement, representing many hours' work, despite the "rat's nest"! Did you consider using multi-core cable?

Circuit Design As described in "A Test Track in N - 4: electrics" I started with an emf-sensing feedback design by Jonathan Scott (www.scottpages.net/UniversalTrainController.html second circuit from top). It was intended that the controller would be powered from AC, DC or battery to enable my N test track to be used 'anytime anywhere'. Construction I made a few small changes to Mr Scott's original circuit: C3 to 3uF to reduce inertia on a small layout add 1000uF reservoir/smoothing capacitor across the supply rails (I'm never happy running op-amps from raw unsmoothed DC even if they will work that way) use a 3-pole direction switch with the 3rd pole switching a red LED to warn of reverse before the knob is turned. Having gathered all the parts together, the big question was, "Will it all fit in there?". As this is only a small, one-off circuit, I decided against making a printed circuit board. So a piece of copper SRBP stripboard (aka Veroboard) was cut to fit in one of the slots helpfully provided by the box manufacturer. Then components were placed around the op-amp IC according to the circuit diagram - a few wire links were required to hop between strips. Everything fitted except for the bridge rectifier which was bolted to the box base. Very careful measurement was necessary to ensure that no components would foul the speed and direction controls mounted on the lid of the box. Then it was a case of cabling the various bits together: rectifier to board, board to switch, speed control and LEDs, switch to output. All wiring was checked twice before proceeding... Testing A 12v battery was connected, quick voltmeter check on the output, place a loco on my test plank, and... movement! But only a crawl, even with the knob up to maximum. Luckily I have access to an oscilloscope - this revealed several interesting things that I probably should have realised before testing: the output waveform never achieves better than a 50:50 mark:space ratio hardly any back-emf in the 'off' pulses the op-amp peak output is ~1.2v less than the supply rail (data sheet confirms it!) voltage drops occur across the bridge rectifier (1.4v), D3 and Q1 (1.3v) Together, this meant the loco only ever received 8v peak and 4v average - no wonder it moved slowly! So I tried a 15v power pack instead of the battery. Things improved - top speed was faster, with great 'creep' control too, but it just didn't feel right. A trawl on t'internet revealed feedback controllers tend not to to work that well with many small motors such as those used in some N gauge locos. Indeed, some tend to get very hot and in a few cases burning out. This wasn't looking good... In a flash of inspiration, I tried a 00 loco on my test plank (it has two tracks). Wonder of wonders - it ran great! Superb creep control, smooth acceleration, reasonable top speed. So this box works after all. Curious, I checked waveforms with the 'scope - sharp 12v pulses, plenty of back-emf in between, and generally 'alive'. Conclusion So yes, a result, but not quite as intended. After considerable pondering, I've decided to keep this controller box for other uses, but make a simpler no-frills DC one for my N test track. Reasoning is two-fold: 1) it doesn't meet my original requirements for multiple power sources (12v battery in particular), and 2) it works really well with 00 locos so it'd be a shame to waste it. The next exciting instalment - part 2 - will cover the simpler DC Controller. Postscript In case it may be helpful to someone, here's what a typical waveform looks like (it varies with loco - I guess every motor is different): Having done further tests, some 'DCC Ready' locos perform less well, with jerkiness at low speed and flickery headlights. But my old Lima pancake motors seem to perform quite well, though sounding raspy. Interesting!

Controller Construction and Test This turned out to be, er, interesting! The details became rather complicated so rather than get bogged down here, I've put all the electronics geekery in a separate blog entry "Make a DC Controller". In summary, I ended up with two controllers, using a simplified non-feedback design for this project. Costs Case wood and hardware - about £17 (carry handle was £5 of that ). Track - about £35. Even discount prices seem to have gone up in recent years... Controller parts - under £15 (+ p&p) but will vary with supplier and what's already in hand. Much cheaper than commercial offerings, though soldering skills are needed, and of course there's no warranty or support. If it breaks fix it! Final thoughts This project did seem to be a lot of effort for a relatively simple, small result. But in the absence of anywhere else to run trains, it has proved really worthwhile. I'd be interested in your comments - it seems very quiet in this corner of the blogosphere... I may add a limited amount of scenic treatment in due course, maybe in one half of the case. First step in that direction will be to make a building to cover the central hinge and provide a sense of scale and context. An open and shut case?

Nice piece! Wiring - or lack of it - is where serial buses realy score. I'll be really interested in how things develop when you have a few devices wired to the CBUS and how you trace any faults unexpected challenges. I've had some interesting discussion with MERG at exhibitions - very helpful and knowledgable folks!

Knockout solution! I thoroughly sympathise with the masonry drilling issue - breezeblock is a real pain! Did you know you can get something called "Mis-drilled hole fixings"? (I have no link with this company) My local (independent) DIY shop sometimes has them, but never when you really need them ;-)

This looks interesting - lots of scope for operation and scenics! Will monitor developments in due course... P.S. Hope this little number doesn't get crossed wires, or hooks any phoney exchange jokes

A simple track plan like this needs only basic wiring: track power feeds on each side of the box connector across the hinge join jumpers to isolated rails jumpers to the toe of sidings. But all wiring is on view when the case is open, so a neat job is called for. Wires were routed under sleepers and soldered to outer edges of rails - with hindsight I should have used something smaller than the standard 2.3mm bit on my X25 iron, and perhaps attached certain wires before fixing track in position. The connector is a 4-way PCB plug/socket with just two pins used; always useful to have spare ways! The longest wire runs are enclosed with U-channel polystyrene strip stuck with double-sided tape. And so to testing. The amazing thing was - it all worked first time! Only powered from a 12v battery with a series 50 ohm resistor, but locos trundled round without de-railing or stopping. Woo! For loco control, it's intended to fix in one corner a box of home-brew electronic gubbins, so that either a battery or a small mains adaptor ('wall-wart') can be plugged in for instant running "any time, any where". So now I'm building an analogue controller more-or-less to a circuit by Jonathan Scott (second circuit from top) using copper stripboard, LEDs, control knob and a polarity switch enclosed in a 80 x 60mm plastic box. So all we need now is to finish that and get it working...

So now we have a wooden box which needs to be turned into a model railway. It's very tempting to start laying track at this stage. But some things need to be done now to properly prepare: apply 'knotting' to prevent knots in the wood from oozing and/or weeping resin later (but omit on parts that will be varnished) paint inside while it's still clean and bare two coats of varnish outside to help protect from inevitable knocks and scrapes (and to "bring out the natural beauty of your wood" ) add catches and a carrying handle. When all this was done and thoroughly dry - over a week in recent cold and damp weather - at last it was time to lay track. I favour a bed under the track to help deaden noise and provide an even running surface. As it was to hand, 1/16th cork sheet was suitably hacked and trimmed, but foam or felt could be used. I decided at the planning stage to use set-track for the main curves - both for assembly speed and to help maintain correct geometry in a tight space. On the track plan, pre-formed track parts are depicted in grey, flex-track in blue. All track is therefore PECO code 80 - although code 55 looks much better, it doesn't mate well with the set-track. Other manufacturers' track could be used if it'll fit and meets the need. Note the short extra piece of flex-track between the two points; this is to avoid cutting into points along the hinge line. For this small layout, I pre-assembled the main oval, positioned it more or less centrally, then marked the rail at the board joints with permanent marker. The tricky bit was actually cutting track in the 3 marked places. I wanted close rail joints across the box halves, but there just wasn't room to use the razor saw in situ. So the pieces to be cut had to be extracted, sawed in a bench clamp and put back in place. It's quite a fiddly job in N - most ended up within 1 mm of where they should be! To fix track to the cork, I used Copydex. In days of yore I always used track pins, so for me this was a first, as many people recommend it for track laying. But be warned - it has a powerful piscine pong! Having roughly laid track on top of the cork, I worked round in sections, gluing track to cork and cork to box, holding it down with heavy items until the glue set (about 20 mins each section). The remaining point and sidings were added later. I had assumed some form of rigid anchor would be required to minimise movement of rail ends when the case is closed. However, the glue seems to hold the track very well, so we'll see how it goes... So all we have to do next is the wiring...

Happy New Year Missy! These trees look great! I'm plumping for 1 Birch, 2 Larch, 3 Scots Pine, 4 Oak, 5 Hawthorn? Not that I know much about dendrology... Nice van too, do I get a bonus point for the wood connection? Tony

Despite wanting this thing to 'be quick to make' I hit an early snag - all is revealed below... One of the key features of this design is that the track will go inside the frame, rather than sitting on top of the frame per the conventional approach. This means: no underboard wiring, point motors etc (a false bottom could be added - but this is meant to be quick and simple) no track pins - unless it doubles as a bed of nails! Assembly tolerances must be quite tight, as even small errors will cause running problems across board joins in N. My joinery is not the best, so this aspect was daunting Here are some of the box parts carefully cut to size and smoothed down: I did consider halving or even dovetailing the joints, but 14mm isn't much to work with, so I chickened out. A skilled carpenter would do it properly. One half of the box glued and pinned and screwed: On starting the second half, it was clear something was wrong. The longest side piece was bowed by about 2mm at the centre - despite carefully selecting timber when buying, rejecting badly knotted pieces and so on. The remaining offcuts I had weren't suitable, so how to un-bow a piece of timber? In fact, it's pretty straightforward for short-ish pieces. Add moisture on the concave side of the bow, then clamp so that an opposite bow is applied. I used a kettle (steam, woo!), a piece of kitchen towel, and a folded plastic bag to retain the moisture, and stuck the whole lot in a vice between two rigid battens for about a day. Then let it all slowly dry out - hopefully straight! If this seems a right ol' palaver, well yes it was, but those odd mm might compromise the result - derailing isn't the sort of test I had in mind! Whilst waiting - two days - there was time to obtain suitable hinges and catches. And also decided to add triangular fillets to strengthen the middle hinge supports. The second half of the box was then finally glued, pinned and screwed. When dry, the hinges were fitted - proving quite fiddly to align and fix all the pieces: - these pics highlight inaccurate chiselling! But at last things are taking shape: Of course, when the box is closed, there is a large gap at the hinge end. This must be covered so that rail ends etc are not damaged in store or transit, but easily removed to enable the two halves to butt together when open. My intended solution is to use a piece of ply/mdf/sheet stuff attached with velcro - with perhaps a couple of cross bearers to act as feet. I'll work out that detail later...

I think I've mentioned somewhere on RMWeb that, like many others, space is an issue for me. So now that N gauge RTR models have improved enormously, that might be the way to go in order to get something running! Plenty of small-space ideas on here and elsewhere for inspiration... But first, new locos would need to be run-in - 'run for half-an-hour in each direction' say the manufacturers' blurb - so a test track would be a good idea. After scribbling with pencil and paper for a while, this plan was hatched: a small 'roundy' to enable hands-off running-in maybe a siding or two to add interest portable and easily stored initially DC, able to handle DCC quick to make and commission Calculations based on dimensions of 2nd radius curves revealed that a nominal 3ft x 2ft oval would fit on a board that could fold in half to make a compact 24x18 inch box. So Anyrail was used to work up a scale plan - this defined the overall case size to be a little larger at 40x24 inches, or 1016x610mm. Each half of the case would need to be about 2in high to provide plenty of clearance for rail + underlay + stock. Here's the track plan: The case parts were then designed: Wood was duly acquired. The sides are a bit non-standard; they are moulded 14mm softwood skirting trimmed to 50mm wide by removing the moulded long edge. The bases are 6mm ply. However, the DIY shop managed to cut the ply out of square on their saw-bench, so the two pieces had to be suitably trimmed square. Doing this shaved a few mm off the short sides - my eventual base sizes were therefore 609x495mm. So all we need to do next is assemble the bits!

Nice neat felt... interior lights...? Nah, must be a new van! :-)