Using LEDs to light model train layouts

"There are many reasons to switch to LED’s instead of regular incandescent lighting":
http://easyurl.net/UsingLEDs

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I have been using them extensively too. I find the surface mount ones the best, they are even smaller than the 3mm ones and they emit light in a broad angle...
How I convert station lamps: http://layout.mixmox.com/1/Marklin-7283 Resistor values for 12V: http://layout.mixmox.com/1/Resistors Determining resistance values: http://layout.mixmox.com/1/LED-resistor
Results Illuminated signal box: http://layout.mixmox.com/1/signal_box In a winery building: http://layout.mixmox.com/1/Faller-130904 As an arc-welder: http://layout.mixmox.com/1/Man-welding Shed light: http://layout.mixmox.com/1/shed-light Tunnel signal: http://layout.mixmox.com/1/tunnel-signal Water crane lantern: http://layout.mixmox.com/1/Water-crane-lamp
Yup, I just love LEDs !
and BTW, don't waste money on expensive ones of certain color, just use a dab of acrylic paint to make them as warm as you want them to be. Takes a just a few seconds.
Dale http://remotesign.mixmox.com

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wrote:

For those of us who are complete novices at LEDs & electronics in general, can you provide some information as to how one would wire a circuit to use them? I seem to remember that LEDs have a polarity to them (which is which), how about resistors? This looks interesting but I'm at a total loss when it comes to even simple things mentioned in the previous two posts.
Thanks...
dlm
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I second that request...in particular I'd like to replace the two constant lighting 1.5v bulbs & diodes with LEDs in a H0 double-ended CNJ diesel.
Ray H.
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Dan Merkel wrote:

Most LEDs output only a very limited part of the colour spectrum, so filtering them with a dab of acrylic paint can only reduce the spectrum further, not change the colour. "White" LEDs have (I think) phosphor over the light output which is activated by the energy output and gives a much broader spectrum light output, so you can filter those with the 'dab of acrylic' method.
The long lead is the positive one.
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yes I start with only white LEDs. White LEDs are really blue plus some chemical trickery.
starting with white LEDs and adding acrylic paint I am able to produce lights that range from fluorescent looking to incandescent looking - as you can see in my photographs of the results. (and they do look better in real life than the photographs)
Dale http://layout.mixmox.com

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I can never remember which lead is + or -. I connect the LED to a 1.5V source. If it lights, I have it right. If it doesn't I reverse the leads. If it doesn't light then, it's no good.
Connecting the LED to a low voltage source like that won't harm it if it's backwards. It's a diode, after all.
--
Bill Kaiser
snipped-for-privacy@mtholyoke.edu
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On 6/15/2008 8:42 AM snipped-for-privacy@mtholyoke.edu spake thus:

Yep, true that.
In fact, if one is handling a lot of LEDs and wants to identify polarity quickly, one could build a little testing rig out of a 1.5 volt battery holder and a couple of wires (color-coded) connected to alligator clips.
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Use a 6V battery and a 1K ohm resistor. 1.5V isn't enough to cause all LEDs to forward conduct (and glow). And hooking an LED up without a resistor is playing russian roulette. Forward voltage varies greatly with color. 6V should be less than the the reverse voltage limit and is more than enough to light up any SINGLE LED.
--
Clark Martin
Redwood City, CA, USA Macintosh / Internet Consulting
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David Nebenzahl wrote:

(Yes, this is months later, I'm catching up, oh well.)
I can envision getting (or having on hand) one of those little white(ish) "experimenter's block" things from Rat Shack, generally intended for putting ICs down the middle and ancillary components next to their leads.
They are particularly adapted to just shoving component leads into them and then yanking them out again (okay, pushing and pulling them carefully), without requiring clips or clamps etc.
HOWEVER, if I understand what I have read here correctly, the presence of all those nifty little holes for the leads from the LEDs (haha) should not be taken as an invitation to test them all at once.
If someone can explain how to do that after all, that would be a plus. (Ouch, sorry.)
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On 1/11/2009 4:53 PM MangroveRoot spake thus:

Yes; they're called "experimenter's boards", "prototyping boards", "breadboards", etc. (People used to use real breadboards back in the day, hence the name.) Very handy little things they are. Don't go to Radio Shack; go to a *real* electronics store (if you're lucky enough to have one nearby). RS is a ripoff.

You could test a bunch at once just by connecting them in parallel, so long as you have a current-limiting resistor in series with the bunch. Probably easier just to test them one at a time, unless you have dozens to go through, since if you don't know what polarity they are, they could either be bad or connected backwards. (I don't know the rules for identifying LED polarity; maybe someone else here does.)
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(I don't know the rules for identifying LED polarity; maybe someone else here does.)

Look at the LED from the side. One wire leads to the base of the substrate which emits the light, the other is connected to a very fine wire leading to the top of the substrate. The one leading to the base is the cathode (-), the other is the anode (+). LTG :)
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Not always - some have reversed layout. Not very common but they do exist.
If the LEDs are new then another possible clue is the length of its leads - longer is positive. Sometimes the collar on the bottom of the LED case has a flat spot on it near one lead - that is usually negative.
I made a very simple LED tested which I have been using for years: Take an old 9V battery apart and save the top cover which has the contacts on it. Take a small piece of copper-clad PC board (about 3/8" x 3/8") and cut the copper across the center (dividing it into 2 isolated copper areas). Solder one side of the copper board to one of the battery contacts on the back of the battery cover. Solder a 1/4 or 1/8W 1k ohm resistor, one end to the other copper area and the other end to the other battery contact. Snap your "LED tester" assembly onto a new 9V battery. To test an LED just place each of its legs on each of the copper areas of the PC board. If it doesn't light up, reverse the LED
Peteski
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What a good idea!
Thanx!
~Pete
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On 1/12/2009 11:06 PM Twibil spake thus:

Hey, here's an even better idea (inspiration from the Pete 2 messages back): take that 9-volt battery top and solder a wire to each connector. Solder a small alligator clip to each wire, with that 1K resistor in series with one of them. Voila! A handy-dandy LED tester that grabs the leads of the "device under test".
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On Mon, 12 Jan 2009 22:21:36 -0800 (PST), Peter W. wrote:

And then mark the positive lead with a spot of paint.
--
Steve

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To make things simpler than taking apart a battery, the connector for 9V batteries connecto together. Just put a resistor in one lead and put a 1 pin connector on the end of the wires and plug in a LED and see which way it lights. I would use a 470 ohm resistor which will keep the current below the max. 20mA that most LEDs are rated for. LEDs are always marked with either/both a flat or notch in one side and a longer lead to indicate to the assembler which way to put in the LED.
-- Bob May
rmay at nethere.com http: slash /nav.to slash bobmay http: slash /bobmay dot astronomy.net
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I was keeping my tester design as simple, cheap and compact as possible. 1k ohm resistor is even safer than 470 ohm and the LEDs still light up.
Peteski
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Agreed.
-- Bob May
rmay at nethere.com http: slash /nav.to slash bobmay http: slash /bobmay dot astronomy.net
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ON those breadboards, all of the 8 or so holes adjecent to a the slot are all connected. On ones with more than one set of slots, the narrow slots are where the gap[ is and there is no connection to the other parts of the board. You don't want to put the LEDs in parallel as they will all tend to have different brightess levels as the lower voltage ones will draw more current and the h9gher voltage ones will draw less current. Putting a number o9f LEDs in series will work if you have a somewhat constant current source as it is more the current that generates the light rather than the voltage. You will find tho that it will be easier to just put one LED in and then see if that works due to the assembly time it takes to put in several LEDs to see if they work. Additional problems with putting several LEDs in parallel for a testing envoriment means that you have to disconnect the power or you will pop the LED as you put it in the tester as it will be overcurrented and will overheat, destro9ying the LED. LEDs can take more than 20mA but only for very short periods with long rests inbetween to keep the heat down. Arrays of LEDs are often scanned to minimize the necessary electronics driving them.
-- Bob May
rmay at nethere.com http: slash /nav.to slash bobmay http: slash /bobmay dot astronomy.net
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