LED and wheel set Questions

I liked the article and I would like to have seen a hand drawn picture layout of all parts or a schematic as I am an electronics newby. 

I thought the wheel sets were insulated from the axles on both ends?  Do the IMR wheel sets have only one wheel insulated?

Mr DCC's Workbench - Your Digtrax system can wake up happy!

I own the Digitrax Superchief system along with about forty additional Digitrax DCC components, decoders and controllers.

You are absolutely right about Digitrax System manuals defying logic with strange and missing explanations. Check out the section on programming modes for an example with several gaps in explanation that make the section confusing and incomplete. I have even seen an instance in one of the Digitrax decoder sheets that refers the reader to the Digitrax system manual, somehow missing the possibility that the decoder owner may not have a Digitrax DCC system! Laughable.

I lean heavily on my technical background to make sense of the poor explanations and guidance in Digitrax documentation. Too frequently, there is something missing, confusing or odd. My non-technical friends who own Digitrax systems tend to rely on tribal knowledge to get their systems to function as intended. Doesn't that seem like a squandered opportunity?

Given that the Digitrax system and controllers contain a fist full of buttons and options, and that very little of the Digitrax system operates in an intuitive manner (there are many more in addition to the items noted in your column), one would reasonably have expected the company to put significantly more effort into their manuals which are intended to explain how to use and program the various Digitrax components. 

Regrettably, they have not. As you can see from my purchases, I see plenty of potential in the Digitrax system, but it is mystifying to me as a customer why they skimp on the documentation that makes it usable!

And have I communicated the challenges with Digitrax documentation to Digitrax? You bet. I received no response.

Steven

Your digitrax system can wake up happy

Finally some clear language instructions on Digitrax.  The convoluted or missing documentation is so frustrating our club is seriously considering switching to NCE.  Luckily, there is still a market on eBay for Digitrax systems

One of the best sources for

One of the best sources for information on undocumented things with Digitrax is the Yahoo Digitrax Users Group (Neo format and all... grrrrr...). There's almost nothing they don't have in their collective wisdom (over 11,000 members!), and it's far less expensive than replacing your entire system. (membership is free).

Frankly, I don't think any other modern control system, DCC or or otherwise, is any better when it comes to documentation... and many are far worse... or just don't have enough features to bother with writing documentation.

Joel, is it?

Has anyone ever tried light-sensor lights?

Hi,

Really a nice column!

Has anyone ever tried to install a light sensor to switch the interior lights on and off?

Using an LDR (photo-resistor) or a photo-diode/transistor this should be possible with three or four simple parts. The interior light (LED) gets switched on when the car is in a dark spot or the room light gets dimmed. It switches off when in bright light.

It is probably a good idea to install the sensor outside the lighted car (on the floor or in an enclosed compartement - e.g. in the restroom)?

Would be nice to hear if anybody tried before I do

Have fun!

JMRI to the Rescue -- Again

For those users with JMRI managing a Digitrax Command Station only requires a few clicks. From DecoderPro LocoNet Tab menu click Configure Command Station to open the switch menu. Set switches as appropriate then hit the Write button to save them to the command station. Done! If things are really messed up Closing switch 39 will reset internal memory setting all switches to the Thrown default.

Another idea

I would think that it would be far too sensitive to ambient light conditions.  It would not be prototypical to have the car lights coming on and going off every time the car went underneath something, or was in a shadow.

However, if all of the cars had function decoders which were programmed to the same address, a single command could turn all of the lights on the train on or off.  I'm not sure if a function only decoder can be part of a consist, or if it would still react to a function button if it was part of a consist, but if so that would allow you to keep unique addresses and still control all of the lights on a given train simultaneously.

No, the lights in passenger

No, the lights in passenger trains don't necessarily function with ambient light... but they DO function according to time.

Suppose some smart guy wrote a "throttle" that linked to the fast time clock in the DCC system, and turned coach, sleeper, lounge, dining, and observation car lights... as many as 4 different ones per car... on and off without intervention from the engineer? Even better, what if some smart manufacturer made accessory decoders you could put in rolling stock, so you could do this without using throttle slots? Then it could link to the dispatcher's panel, and be controlled by the clock there. Once programmed, the whole thing would require no human intervention. The lights in the passenger cars... and why not? at the stations and even in town... would all operate seemingly independently.

We haven't even begun to scratch the surface of what DCC makes possible yet...

Wheel set question

To answer the wheel set question in joeldee's post, yes IMR wheel sets are only insulated on one side.  If you look closely at the joint between the wheel and the axle you will see the black insulator only on one side.

I think all HO metal wheels are only insulated on one side.

If I'm wrong I would expect someone to correct me.

Humm? 4700 uF Power Storage

Maybe OK with no current snubber if there in only one on the layout. Grabbed a 1.25 Amp bridge and a similar Nichicon VX series 4700 uF 35 V cap. Hooked up a Digitrax DCS 200 with a current probe on the DCC output. Powered on - Only about a 10 Amp spike and a beeping DCS200. Over current shutdown, but recovered after third cycle. OK need larger booster. Grabbed NCE PB110 (10 Amp Booster). A little lower source resistance resulted in a 12+ Amp spike, but the NCE did not fold back. Now I added two more bridge / Cap pairs to the load. Now the NCE is not happy at power on with 28 to 30 Amp spikes and one blown bridge. Now I usually run eight to ten Bachmann Passenger cars so ten cars at 12+ Amps each would = bad startups. Solution - add a resistor / diode pair to the capacitor as in the hold up circuit in figure 4 of the March 2013 MRH DCC Impulses column.

Replaced blown bridge and added snubber circuits to three caps. Surge current less than 1/2 Amp. Checked with ten Bachmann Chattanooga Choo Choo cars wired in a similar manner and measured a surge current of under one Amp. DCS200 (8 Amps max) runs ten car passenger train pulled by a pair of Annies with no problems. 

Note that these test were conducted at 21 volts as some Bachmann Shays with stunted Tsunamis, which also run on this layout, have problems with higher voltages. So these test were not as stressful as they could have been at max NMRA recommended voltages.

Why is it

People start their comments with the subject?

Don't people realize where they are typing or how much harder it is to read?

The post on the 4700 uF cap Power Storage made absolutely no sense the first time I read it.  Until I realized the Mabye OK sentence should go with part of the subject, of course may be should have a space too...

Currently it reads as follows:

Subject:

Humm? 4700 uF Power Storage

Body:

Maybe OK with no current snubber if there in only one on the layout.

Where as if it was written as follows:

Subject::

4700 uF Power storage current

Body:

Using just a 4700 uF cap as power storage may be ok with no current snubber if there in only one on the layout.

Of course it had me wondering at first only one what? on the rest of the layout.  When it comes to electronics you need to be as clear as possible.  The next sentence "Grabbed a 1.25 Amp bridge and a similar Nichicon VX series 4700 uF 35 V cap." I wonder similar to what?

I may be the only one but what do you mean by "NCE did not fold back" ?

Please take this as constructive criticism and not a negative bashing post

Enjoyed Sept article, but have a question.

Bruce-

Thanks again for another great article! I was able to build a circuit and power an LED. After cutting the power the LED stayed lit for 4-5 seconds before fading out.

Is it possible to add something like this to an engine to prevent headlight flicker? How would that be wired with a decoder?

Eric

Digitrax Documentation

It is a real shame that Digitrax did not make their system more intuitively user friendly.  What a novel concept to let the computer do the hard stuff for you.  Then the manual wouldn't be as critical to making the system work.  I never cease to be amazed that so many people buy this system.

Digitrax is very good at marketing

Digitrax does a very good job marketing their system, and it has very strong brand recognition. There's no question their locoNet is brilliantly engineered, but it's also true their system user interfaces and their manuals do have shortcomings. Connecting with other local users can really help when you have questions - and that's pretty easy because the system is so wide-spread.

I do think there's a market for "The missing Digitrax Manual" that captures all the tribal knowledge and would explain things in less technical ways. If anyone would like to talk to us about authoring such a manual, please contact us. We're interested in helping fill this gap and we think it would sell well (read: some good hobby mad money for the author).

Headlight flicker is a GOOD thing.

Exactly, clean your track instead

Lighting your rolling stock

Thorough article. I'll refer back when I'm modeling my next car. Isn't it true that some early (19th Century) passenger trains had little or no lighting?

In the 1870s Passenger cars had four lamps per car

Yes, many of the very early cars had very limited lighting, by the late 1880s you might have up to four double lamps per car using either light oil, or pressurized gas systems.  The Santa Fe was using electric lights by the early 1890s.

I understand clean track/good wiring, just annoying

I just find it annoying when a engine stutters for that split second at a switch and the head lights flicker or the sound restarts, etc. Maybe the next layout I build will include powered frogs to help eliminate this problem.

Eric

Function-Only Decoders and Consisting

Stuck and frustrated

Dear stuck and frustrated

First, try an AC measurement. A DC meter will only measure the average of any AC that is getting through. It is the peak voltage that blows LEDs. Second, what size capacitor are you using? A bridge rectifier will normally give you a one sided waveform with peaks nearly the same as the input wave. (The negative side of the wave is reflected as a positive loop, so you get all of the power of the original.) The capacitor filters the waveform to produce a steady DC, but only if the capacitor is big enough.

The calculation goes like this: The resistance of a circuit (in ohms) times the capacitance (in farads) gives something called the time constant (TC) which is the time that it would take to charge or discharge the capacitor 63%. (Skipping a bunch of calculus here.) A good rule of thumb for smoothing rectified AC is to pick a time constant around 100 times the period of the input. The period of DCC goes up to 10000 microseconds under some circumstances, so the target TC would be 1,000,000 microseconds or 1 second. With 750 ohms circuit resistance, (the LED doesn't enter into this) a 1333 microfarad capacitor will do the job. They don't make 1333s, but 1000 microfarads will do. Capacitor voltage must exceed peak voltage, so pick a 35 volt rating. The capacitor is connected between the + and - pins of the rectifier (if you get this backwards, the cap will go pop!) and the resister and LED are in parallel with this.

That's for one LED. If you have several in parallel, their resistors will also be in parallel, so the equivalent R will be less.  Assuming the resistors are the same, multiply the capacitor value by the number of LEDs. If you want a longer time constant to keep the lights on across frogs and so forth, increase the capacitor value accordingly.  If you want to hang a voltage regulator on this to get 9 volts, use a 7809 and follow the example in the data sheet. Note that a couple of smaller capacitors are recommended- use those in addition to what is described above.

Incidentally, the current snubber logger01 recommends would be a  resistor between the + output of the bridge and the big capacitor. Value is 40 ohms or so at 1/2 watt. This keeps the capacitor from sucking too much power from the booster at charge-up time. (The booster sees a short for a few milliseconds.) This also lowers the voltage at the capacitor, so you will want to measure that and adjust the LED resistor. The circuit as shown gives the LED 25 mA.

pqe

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