TimberSurf’s Model Railway  

Lumsdonia Railway

A web page for my indulgence and sharing ideas and irregular updates on my Model railway

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   ELECTRICAL - Section 200

Tips 200

Computer controlled (compressed time cycle) layout lighting = running a 24 hour cycle of on/off lighting control to simulate a "day" but over a shorter duration (i.e. 2 hours see's rotation through daylight to night to daylight again, then repeats)

Some sophisticated layouts are run to a timetable, so its my intention to do similar, but to a compressed time. This will include the layout functions (lights, motion action accessories, etc.) to be synchronised with the train timetable.

It would be possible to do with electronics (4017's chained together) or with the likes of PIC chips or programmable IC's like Arduino, but my preference for ease, is a PC.

Much investigation lead me to an inexpensive ready made solution called LEDWiz (for pinball machines) that gives (PC) USB control of 32 channels. There are many 1,2,4,8 and 16 channel relay output cards available for PC control, but this only gives on/off control. The advantage of the pinball card is that not only do you get 32 outputs (for £30), but each one is completely variable in intensity (255 steps). This not only means complete control of timing, but also maximum final intensity and variable intensity on the fly (special effects). There are four banks of 8 outputs, each could have a different operating voltage as it switches the -VE (neg). If the supply is 5V, then no resistor is needed for LED or 6v Bulbs, or a higher voltage can be supplied (12v, 24v, etc.) but with an appropriate current limiting resistor.

Various special features can be added programmatically, such as Sodium pre-ignition, Sodium starter fail, gas light flicker, TV multi colour flicker, belisha beacons, traffic lights, etc. The list is endless!

There is also a 16 input/16 output card, so reactive elements could be introduced (buttons, red switches, block control, etc.)

My intent is to have a on/off/on switch per channel, giving permanently ON (test/manual), OFF, and ON (Auto controlled by PC). Housed in a small control panel box, the outputs will be connected to a 37 pin D Sub connector (detachable from layout for testing, moving, rework, etc)

I have written the base code in Visual Basic in a spread sheet, but at a later point, once refined and beta tested, may migrate to an Exe file for distribution as a standalone.

Top right  is a quick circuit sketch, note the PSU I am using is 10A, so I will be fusing 4 circuits to something like (20ma x 30 leds = 600mA) 1 Amp per quarter of the board. {Alternate channels used for clarity as an example}

Below is the Excel spread sheet front end

To have sounds playing in the background like station announcements, workshop noises, cows mooing etc, install this PCB in a building or under the layout. For less than £2, from china, a MP3 Decoder TF Card Slot U Disk Decoding Player Module PCB, needs a 5V supply and has on board 3W Mono Amplifier.

Add a 4-8ohm speaker and a (£1) Micro SD card (2gb) and your in business! Just power up for continuous background noise (it has volume control) or connect wires to pause or repeat button to start action sounds on demand.

Its really loud, and very flexible. only plays mp3's but the sound quality is excellent (32gb would give 99 hrs. of sound) Also takes USB sticks (we all have them lying around useless as they are now too small [256mb would give 40mins])

Demonstration video Background Railway sounds

To have sounds playing in the background like station announcements, workshop noises, cows mooing etc, install this PCB in a building or under the layout. For less than £4, from china, a MP3 Decoder TF Card Slot U Disk Decoding Player Module PCB, needs a 5V supply and has on board 3W Duel Amplifier.

Add two 4-8ohm speaker and a (£1) Micro SD card (2gb) and your in business! Just power up for continuous background noise (it has volume control) or connect wires to pause or repeat button to start action sounds on demand. The sound recording could be two separate sets of sounds and the two speakers positioned far apart.

Its really loud, and very flexible. only plays mp3's but the sound quality is excellent (32gb would give 99 hrs. of sound) Also takes USB sticks (we all have them lying around useless as they are now too small [256mb would give 40mins])

It also has a remote control, so can be adjusted/indexed by hand

Demonstration video Background Railway sounds

It troubled to me, that to check the resistance of silver paint (or circuit works) when used to bridge the insulator on metal wheels, for lighting pickup or just as resistance for block detectors (guards van or tail wagon), my multimeter will barely measure down to a few ohms!

You could make a sophisticated Wheatstone bridge, but the variable resistor would be very expensive! It occurred to me that a simple voltage divider (two resistors in series) with a little calculation would be sufficient! A few tests later and a purpose made test lead was made up! Now I can just attach my test lead to one side and +5V and the other side (black one) to -5V PSU [a stable supply is not necessary, a 4.5V battery pack would do]

All you need is a multimeter that measures volts, millivolts, and ohms

100-220 ohm resistor or thereabouts (preferably 1% and 1-3 watt)

5 V regulated power supply (wall wart, bench supply, or 7805 circuit, or even a battery)

Put the high accuracy, high wattage resistor in series with the unknown, across the 5V. Measure the voltage (drop) across each and do the maths

Unknown low resistance in ohms = Unknown (R2) millivolts / 1000 / (R1 volts / R1 resistance)

Full write up can be seen here http://www.robotroom.com/Measuring-Low-Resistances.html

Bring a new dimension of SOUND to your layout

Find or make recordings on your PC and play “background” noises like station announcements! Examples

A bus for DCC is not obligatory!

A bus serves two purposes, one to ensure a low resistance path to all parts of the track and two, to supply ancillary devices around the layout! There is no reason that lots of spurs (pairs of small wire) could not be wired individually to several points around the track and ancillary points! Its just easier to have a 2 wire bus rather than big bundles of wires running from the supply point.

Were it is important, is on a large layout were volt drop gives a huge impact. On a small layout (and that probably means most UK modellors) it is less important. There are also a few other factors that make an impact.

Volt drop = I x R. So if the loco draws 1 amp, and 40ft equates to 3 ohms resistance , then volt drop is 3 volts, but if the loco is more modern and only draws 0.3 Amps then the volt drop is only 1 Volt!

If there is a fishplate every 1 meter, on a 4 meter long track, there is 10 times less chance of a high resistance fishplate joint, than a 40 meter long track.

On a large layout on DCC there will be 4-10 amp boosters, with the possibility of running consists drawing several amps, therefore a large volt drop due to the large loco current, if only a small layout and a small controller is used < 2 Amp (usually only 1.2 Amp), then the maximum volt drop is less (defined by the max output of the controller).

So you see that on a smaller layout, going mad with a bus is not really necessary. It is certainly good practice and I would recommend supplying lets say a 3+ meter long layout with more than 2 droppers (one at each extremity and say the odd branch line and individual sidings (as they should have IRJ's if electrofrog) and perhaps more if the track is not all flexitrack (std track will have more fishplates)

Linking across fishplates will certainly eliminate the risk of bad fishplate joints, but it will not improve the volt drop on a large layout. The same goes for the American habit of soldering all rails, it certainly eliminates bad electrical joints over simple fishplates, but it does not solve volt drop issues.

So a DCC Bus is a good idea and good practice, as is frequent droppers (connections to the track)

It achieves the following:-

Eliminates high resistance (bad electrical connection) in fishplates

Reduces volt drop on large layouts

Allows ease of multi connections to multiple tracks sidings etc

Aids fault diagnosis

Allows connection of distributed accessories

Low resistance for large layouts to clear shorts on large boosters

My principle (and its a personal choice) is to have feed wires to every 2 meters of track (one of the reasons being that I will have block detection and braking sections every 4 meters) but I would have at least 1 dropper per 4 meters (i.e. 4 x flexitrack lengths) as a minimum, this ensures I only have a maximum of 3 joints per dropper, that might give trouble (easy to diagnose if they do, as a very small section)

I would also advocate on a booster supply (> 2 Amp) to not only use districts but also create sub districts that are protected by electronic fast fuses or the "21W lamp in series" current limiting bulb.

See TIP604 for wire sizes

Top soldering tips

Turn it off if your not using it. {the tip is oxidising and reducing its life}

Constantly clean the tip and re-tin it {easy if done regularly, hard if left long}

Use flux cored solder {why wouldn't you? Flux is the key to good soldering}

Pre-tin both parts, then solder together {else your trying to do three jobs at once}

Use flux as well as fluxed cored solder {the secret of good soldering}

Clean metal surfaces immediately before attempting to solder {coat with flux if to protect if not soldering straight after cleaning}

Keep temperature as low as possible while maintaining enough temperature to quickly solder a joint (2 to 3 seconds maximum for electronic soldering).

Match the tip size to the work {the bigger the better for thermal transfer, lower temp setting, faster joint, less collateral damage}

Use a tip with the shortest length possible for maximum efficiency {better temperature control}

See Soldering Guide for guidance on which soldering iron/station to buy or use