DCC and Headlights

[CaptOblivious]

Some folks here have been askin' about wiring up decoders to headlights in end cars. At the urging of Bernard, I've written an introductory article on the subject here: http://akihabara.artificial-science.org/?p=52

If you've got a train, and you're unsure how to make the endcars work on DCC, I suppose this would be the place to talk! Post pics of the circuit boards, or if you can find your Kato model on this page: http://www.katomodels.com/hobby/dcc/dcc_tips/light_kato.shtml I can just use those cool little diagrams Kato drew up to help you out.

[Bernard]

Capt,
Thanks for an excellent explanation! I have a question could you use Kapton tape to isolate the head light unit from the track feeder pads?

[CaptOblivious]

I'd like to note that I have updated the post: I was wrong, in that the treatment for both endcars is is different that what I had first claimed. It's been corrected now.

Bernard: Yes, you could use kapton tape to isolate the cars. In this case, however, you'll have to find a different place to cut the traces to isolate the LEDs from each other, and a different place to solder the wires.

Also, you've probably got a different circuit board than the one I used in my illustrations. Check this page: http://www.katomodels.com/hobby/dcc/dcc_tips/light_kato.shtml I bet you have the 37601 style board, which will have its own set of issues.

[Bernard]

Capt,
I wrote to Tony's Train exchange about the Kato Head & tail lights and as you said he also recommends the Digitrax TF-4 or the TL-1 (which I can find in his product list) here is the link:

http://www.tonystrains.com/products/digitrax_decs_small.htm

Wow, I think we've hit an area where I don't of a lot of people who have done this installation. It's so much easier to do a motor install than the lights but now I'm curious to do it.

[CaptOblivious]

The TL1 has only one function output: Which means, if you have both headlights and taillights, you will need two TL1s to light the car properly! Cheaper to use the TF4, with its four outputs. If there's only a headlight, then the TL1 is a good decoder.

Bernard, would you mind posting some photos of the interior of the endcars and the lighting circuit boards on your 500 series that you want to wire up?

[Bernard]

Here are 4 photos of the 500 Nozomi train. 1 is the train, 2-is the interior 3-is the top of the Head & tail light unit 4-is the bottom side of the unit.

[CaptOblivious]

Nice shots! Perfect. This will be easy as pie. Thanks for getting that, Bernard.

First, let me note that the tutorial on my website is mistaken in one important way, (and I'll be fixing it shortly!!) . According to the Digitrax Decoder manual, the function leads should be connected to the cathode of the LED; the cathode is the side with the big electrode inside the LED. In "Light Unit Top", above, this would be the top side of the headlight and the bottom side (relative to the photo) of the taillight.

Anyway, here's how I would do this. I would follow largely the suggestions here: http://www.katomodels.com/hobby/dcc/dcc_tips/light_kato.shtml (very last diagram at bottom)
But not entirely! The LEDs on your board are configured differently than in that diagram. Nevertheless, cut where the diagram says cut (you may have to wait until you remove the red LED to make one of the cuts, see below). If this is the head car, solder the red lead from the decoder to the bottom (relative to "Light unit top") pickup pin-like thing if this is the trailing car, solder the red lead to the top pickup pin. The black lead goes to the other pin.

Now, desolder the cathode of the headlight (that's the top lead in "Light unit top"). Solder the white F0f lead (if this is the head car; the yellow F0r lead if this is the rear car) from the decoder directly to the headlight cathode (the bit you just desoldered). Tape that up real good, or better yet, use a length of heat-shrink tubing to keep it from shorting anywhere, now that it's sort of dangling loose.

Then, and here's the tricky part, bend the red LED so it's point backwards. Careful! Then desolder it from the board. While it's out, this would be a good time to make that tricky cut I mentioned before. You'll need to sop up all that excess solder with a desoldering wick first, though. Reinsert the red LED it so its facing forward again, then solder it back in. (Alternately, only solder in the anode)

Finally, solder the yellow F0r and blue common return leads as indicated in Kato's diagram. Unless this is the rear car, in which case solder the white F0f lead where the diagram says to solder the yellow lead.

I'll whip up a diagram of what I'm talking about in the morning, to help make this all clear.

Of course, you'll want to cut all the decoder leads shorter than they are, so they don't go all in the passenger area. I'm not sure where the decoder will physically fit; I can't tell in the photos.

Hope this is helpful!! I really look forward to seeing this work for you!

[CaptOblivious]

Here you go.  ;D

[CaptOblivious]

The second part of my DCC headlight tutorial is up!
http://akihabara.artificial-science.org/?p=62
read and enjoy! I hope these are useful for y'all  ;D

[Bernard]

CaptO,
Excellent tutorial. I just got the digitrax TF-4 and one of the instuctions is to program the decoder before installing. Okay no problem but what address do I give it? My 500 Nozomi's address is 005, would I assigned the same address number to the TF-4?

[Martijn Meerts]

Given the function decoders the same address makes sense, since that way you can easily turn on/off the direction dependant heald/tail lights without having to switch to a different address. So for a full train you'd end up with 3 decoders with the same address, or if you're really into it and add decoders to control interior lighting, you might end up with 16 decoders with the same address =)

[Bernard]

Ahhhhhh! 16 decoders in one train, wow, that's one expensive shinkansen, no wonder they only made 9 Nozomi 500s! (joking)  ::)

I had a feeling that keeping the same address would make the most sense I was wondering it there would be a confusion when you call up the train when programing. I was surprised that you have to pre-program the decoder before installing. I wonder why you can't asssign an address after you've installed it since it's in a separate car. It's going to be interesting

[CaptOblivious]

They suggest pre-programming, because in most cases, you will be installing it in a loco that already has a decoder. In your case, you can just  put the end car on the programming track by itself, and program the installed decoder. If you were adding functions and transponding to an already-chipped loco, on the other hand, having two decoders with different addresses would make programming different values into the same CVs impossible. (Digitrax uses something called "decoder locking" to make it possible, but it still requires some programming of the decoder before you install it.)

[Martijn Meerts]

I've never pre-programmed a decoder. What I usually do is a temporary install without cutting any of the wires to length and just hooking up the motor outputs. I use this setup to program the decoder and do some initial testing. I then cut the wires to length and mount the decoder using the included double sided tape pads. Only then will I start playing with the lights.

I've been considering building a decoder tester, using some LEDs and an old motor, but haven't gotten around to that yet.

As for programming, I do most programming on a programming track, or a test-stand connected to the programming track outputs nowadays. This does mean of course that you can't have 2 decoders on the programming track, since that would mess things up.

[CaptOblivious]

I've never pre-programmed a decoder. What I usually do is a temporary install without cutting any of the wires to length and just hooking up the motor outputs. I use this setup to program the decoder and do some initial testing. I then cut the wires to length and mount the decoder using the included double sided tape pads. Only then will I start playing with the lights.

That's good advice right there, Martijn. And if you do put together a tester, would you post schematics? I find hooking the decoder up to a motor to test it much easier than using the bizarre LT1 testing-harness that Digitrax supplies with their command stations.

Bernard,
My previous comment about doubled-up decoders was a bit confused and perhaps confusing, too. What I meant to say was more like: Two decoders on one programming track=bad. Two decoders with same address in any programming method=bad, for what should be obvious reasons :D. The TL4 installation instructions assume that one or both of these scenarios will obtain, and this is why they want you to pre-program. But since neither will be the case for you (Bernard), you don't need to worry about pre-programming.