Resistor Question

Model Railroader Electronics and DCC
1

I have a quick resitor question. I’ve been wiring up LEDs in various setups for several months now. I’m currently working on a scratch built project with multiple series of LEDs setup. Between 4-5 series per building. The problem is, one of the models I did during daylight hours, so it was not until evening with the lights off I discovered I’ve chosen resistors too low for the exterior lights as they are taking away from the interior lighting through the windows. I would like to avoid refitting all 4 series on the exterior lights with alternate resistors.

So my question. Instead of said refit, can I simply add a single resistor were all series come together? I have the wattage covered with a resistor for this, but I am wondering if there are any complications to this, as I am still just surpassing the novice level with electronics.

I understand a lot of the basic do’s and don’ts of wiring LEDs with resistors, like never supply multiple LEDs in paralell with a single resistor, etc. but even though this situation seems to work fine in my mind, I just want to be sure.

Thank you for any advice. Hopefully to photo shows up correctly.

Pic2Pic1

2

Bucktoof:

You should be fine by simply adding a resistor to the supply for the four LEDs. You are already aware of the wattage issue so I don’t think you are likely to set your layout on fire.[swg]

By the way, that is a really nice scratch built motel!

Dave

3

I agree with Dave, nice looking model.

What I often do is sort of the opposite of how you ended up. I’ll frequently add a higher wattage (typically half watt) to the main supply for a building or a section of a larger building. That handles the protective function and tones everything down. Then I vary the different groups of lights by using additional resistance. This provides a less uniform lighting scheme, which is usually more realistic than uniform lighting throughout.

Another approach is to use some sort of diffuser over the too-bright LED. I tend to favor small sections of Evergreen tubing, sometimes I’ll even cut them in half. This can also be painted for even better custom work.

4

Thank you both, Dave and Mike for the advice and compliment. I think it’s a good idea from now on to use a nice beefy resistor ahead of the rest, both for ease of tweaking lumenation and extra protection. I’ve always been extra mindlful of the safety part because all my models are, in their core, balsa which tends to burn faster than my paycheck in my wifes hands.

I have some plastruct tubing and channels of various sizes. I haven’t thought of diffusers or even hear of it 'til now, so thank you again. Perhaps even light colour card stock which i used to cover my models will work as well. But in this particualr case, the added resistor will suffice. But that gives me wonderful ideas for signage lighting effects now!

There’s 4 motels all together. I usually build 4 of everything in assembly line style, just because it doesn’t really take a great deal of time to make multiples of everything as long as your doing everything in stages.

Heres the rest, although still without roofs which will add second level interior lighting as well. :slight_smile: And thank you again.

Motels

5

Bucktoof

You might be interested in a little experiment that I did a while ago about making internally illuminated signs. Cutting and filing the 1/4" plexiglass was a bit labour intensive. The LEDs are wired in parallel so you have to play with the resistor value depending on how many LEDs are in the circuit. This was one of the first attempts and I managed to mess up the decals. I used 0603 SMD LEDs:

Here is one using 3mm LEDs which are easier to work with but harder to hide:

In both cases I used Microscale decals but it’s not too difficult to make your own decals.

Dave

6

Brilliant looking signs, Dave! I think I’ve just found a use finally for the piece of plexiglass I bought off Ebay months ago that arrived in a rather smashed up state, lol. It is a little thin though, so maybe I will glue two together with epoxy or something and drill some divets around the edges with a dremel to seat the lights.

So the idea of plexiglass is that it will trasmit the light more evenly I gather.

Thank you for the inspiration.

7

Dave,

I was wondering the other day about what You ever did about Your signs. That really was some time ago, when We discussed it.

Bucktoof…Fantastic job on those Motels. [Y] [Y]

Take Care! [:D]

Frank

8

Hi Frank:

The signs are on hold until I make some decisions about exactly which businesses I’m going to model on my street front. At the time I was simply interested in seeing how they would look.

I’ve got all three Walthers Merchant Row kits as well as a stack of City Classics kits for taller buildings so I will eventually need a bunch of illuminated signs. In total there will be about eight feet of store/office fronts. The sign decisions will be largely influenced by what interiors I can come up with.

Sorry Bucktoof - not trying to hyjack the thread.

Dave

9

Bucktoof:

You are correct. The idea behind the plexiglass was to distribute the light more evenly throughout the sign. It is also reasonably easy to cut different sign shapes, although as I said earlier, it is a bit time consuming getting them to their finished shape. Just so you know, I sanded the surfaces of the signs to cause greater diffusion.

Dave

10

Hi,

You can save yourself a lot of grief with a couple more cents expenditure relatively speaking. You did not say what your say voltage supply was but say it was 12 volts and you used a 1 K resistor.

I would suggest using say a 620ohm resistor and a 1K trimpot in series. That way you can adjust the light intensity to that which you find acceptable for your particular lighting conditions and leave it permanently set! Why the 620ohm resistor? Just to ensure your LED’s have some degree of protection

Hope this helps

Cheers from Australia

Trevor

11

A trimpot was a nice suggestion, thank you Trevor. A quick trip to the local electronics supply store and I picked a few up to play around with and got the just results I was hoping for. I routed all the wires from the exterior lights through it and now I can adjust for the right effect I was looking for (well almost, because some series have 3 and some 4 LEDS, the resistor is different so they dim at different rates, but whatever!).

Perhaps on models #2, 3 and 4, I can improve the installation and wire management. Now if I can only decide whether to use a very fine grit black sandpaper for roof, or a lighter grey textured cardstock I think I’ll finally be able to wrap this project up!

Sean

12

Hi, Sean

Might I make a suggestion for you to consider for your roof?

I have tried the emery cloth/sandpaper route and no matter what you do with it — it always looks like… sandpaper!

Painted cardstock is better and layers of tissue laid down with diluted white glue, then painted is pretty good for a “built-up” roof, too.

But, what I have done with some success is download “textures” from this site:

http://www.cgtextures.com/

If you care to make an account, you don’t have to, you can download high resolution graphics, otherwise you are somewhat limited to the file sizes (still pretty big, though).

To take a look at what some users have made using these textures go to About>Showcase

Anyway, I download a texture and use a vector-based (CorelDraw for me but some here have suggested some free ones) graphic program to copy>duplicate>resize then print the texture.

Go to the Roofing>Bituminous menu and see what’s there.

I have downloaded wood paneling, carpeting, floor tile, area rugs, pavement, bricks and all sorts of graphics to use for structure interiors and exteriors.

My printer will print on textured cardstock and this helps with some images.

I have made marble walls and printed on glossy photo paper and it looks very convincing! I’ll try to get a photo or two posted. [edti: done]

Here’s a simple roof on my Brewery:

And the tile work on the floor and walls including the black and green trim was all CG Textures: