color changing LEDs

[hobo9941]

We are told that LEDs need 3 or 4 volts to light.

I have several color changing LED lights for patio and yard use. They operate on a single AA battery and solar charging. They cycle through red/yellow/green/blue. They do not change abruptly, but slowly fade from one color to another. I'm curious if any techies here can explain a few things. Why do these LEDs operate on a single AA battery? How do they achieve the color changes? I feel they could be put to good use in a model railroad situation, especially in single light target signals, if we can figure out the technology. They are also very bright for just 1 1/2 volts.

This is not a problem I need help with. But anyone with knowlege of these LEDs feel free to weigh in with what you know. I think they could be put to good use in a model railroad situation. And they are dirt cheap!

[CSX Robert]

hobo9941

Why do these LEDs operate on a single AA battery?

They have a circuit that boosts the voltage to whatever is needed by the LED.

hobo9941

How do they achieve the color changes?

They actually have three LEDs in one package, red green and blue, and they vary the brightness of each primary color to create a wide range of colors/

[gmpullman]

BLMA does offer a "true color" three light searchlight signal head.

http://www.blmamodels.com/cgi-bin/webstore/shop.cgi?ud=BgUNBwsOAwcFBxQUEBEcHAAFBQEDCAIFCQkTEQAA&t=main.blue.htm&storeid=1&cols=1&categories=01001-00025&&c=detail.blue.htm&t=main.blue.htm&itemid=4001

I have a few but have not installed any as yet. As CSX Robert pointed out they have three tiny LEDs in the package and are lit individually to make the proper color.

I have some other signals that use bi-color LEDs and the "yellow" is actually a mix of the red-green by applying a small AC current to the LED. It doesn't look anything like yellow but either a greenish orange or an orangeish green.

I agree that the LEDs you looked at would make for some fun animated lighting on our layouts. A theater marqee for instance! The technology gets better, and cheaper, every day!

Ed

[gregc]

hobo9941

We are told that LEDs need 3 or 4 volts to light.

Why do these LEDs operate on a single AA battery?

older LEDs operated at voltages closer to 1.4V.   I have boatloads that do.

[RR_Mel]

I bought a few 5mm RGB 4Pin LEDs to experiment with, their voltage threshold is 3.6 volts.  My objective is to use them in single lamp target signals.  I successfully trimmed 5 of them down to 3mm diameter to fit into an HO target signal.

 

I’ve been using 3 pin bi/tri color 3mm LEDs but the yellow or amber has a red or green tint when viewed off angle.  Straight on they look pretty good.  The RGB LEDs appear to work but they require juggling around resistors to balance the yellow and that requires a slightly higher driving voltage.  I’m in the process of coming up with a simple driver to achieve a true red, yellow and green signal head.

 

I’m currently modifying my 5 volt controller to operate from 12 volts to obtain a higher output voltage to drive the RGB LEDs.  At this time I get the best colors with 7 to 8 volts to the series resistors.  The one thing that caught me off guard is the colors (yellow) vary per LED so the resistors will have to be configured for each LED to get a matching yellow on every head.

 

The blue and white color diodes require higher voltage so the red and green in the RGB LEDs also use the higher voltage for consistency.

 

Mel

 

 

Modeling the SP in HO scale since 1951

 

My Model Railroad   

http://melvineperry.blogspot.com/

 

Bakersfield, California

[hobo9941]

Good answers all. Thanks.

[rrinker]

 If you are looking for LEDs for target signals that have a proper colors for all three (most green LEDs are the wrong color for railroad green, for example), check out the ones RR-CirKits has. Not an RGB LED, but a a tri-color LED with specified wavelengths for each color to accurately reproduce railroad colors.

                              --Randy

[mfm37]

Showcase Miniatures has some SMD tricolor leds as well.

http://www.showcaseminiatures.net/n-scale-century-foundry-signals.html

[RR_Mel]

rrinker

 If you are looking for LEDs for target signals that have a proper colors for all three (most green LEDs are the wrong color for railroad green, for example), check out the ones RR-CirKits has. Not an RGB LED, but a a tri-color LED with specified wavelengths for each color to accurately reproduce railroad colors.

                              --Randy

 

 

Good Info Randy

 

I placed an order for a couple of their LEDs to try.  It is not an easy project working with the 5mm RGB LEDs.  First just reducing their size is tedious.  Next it’s a balancing act to get the proper colors and the LED colors are not constant so I have to balance everyone of them.

 

Now another problem is cost.  I need 32 LEDs so $215 for the RR-CirKits is a bit much compared to 50 China 5mm LEDs for $5 free S&H is a pretty big hit.

 

I made a tool to reduce the diameter of the 5mm LEDs but it’s still a lot of tedious and temperamental work just to get them to fit in the signal heads.

 

As I get into my project further I’ll do a post on my blog showing all the work it takes.  

 

Thanks for your input on RR-CirKits Randy!  I just might be worth the big bucks to eliminate the headaches of using RGB LEDs.

 

Mel

 

 

Modeling the SP in HO scale since 1951

 

My Model Railroad   

http://melvineperry.blogspot.com/

 

Bakersfield, California

[rrinker]

Consider the driver circuit you need to get the right colors out of the RGB LEDs. The nice thing about the tri-color ones is thet they work just liek 3 individual LEDs, which most any signal circuit is already designed to drive. You could probably source the LEDs with the same colors from one of the Chinese sources and then come up with your own mounting to reduce costs. For small quantities it might be worth the hassle of a week or so of evenings to put each set together - if you are any good at SMD soldering anyway.

                 --Randy

[RR_Mel]

rrinker

Consider the driver circuit you need to get the right colors out of the RGB LEDs. The nice thing about the tri-color ones is thet they work just liek 3 individual LEDs, which most any signal circuit is already designed to drive. You could probably source the LEDs with the same colors from one of the Chinese sources and then come up with your own mounting to reduce costs. For small quantities it might be worth the hassle of a week or so of evenings to put each set together - if you are any good at SMD soldering anyway.

                 --Randy

 

 

I built my controller so that’s not a problem.  Balancing the colors is a different story.  The reason I upped the voltage from my controller is to compensate for the diode matrix and wide range of resistors.   I’m going to end up making my own resistors because of the weird values needed.  It’s not that hard but it’s time consuming.

 

One of my first purchases when I retired was a SMT workstation another was a large format printer for my CAD drawings.  I had full use of both at work and knew I wouldn’t be able to go without either.

 

I’m a 49 year and 10 month retired Electronic Techie so I really enjoy building up electronic stuff for my layout.

 

I piddled today with a few RGB LEDs and I got several of them to work perfect but it’s really time consuming, it took me about 5 hours to perfect one set of resistors and diodes to get the correct colors from the LED.  I am reasonably content with what I ended up with.  I wired up a socket to plug the LEDs into and found most are pretty close on color, my first tests weren’t very good but today 8 out of 10 LEDs were extremely close in color.  Close enough for a rivet counter.

 

Either way I go I’ll need four colors of #36 or #38 gauge wire so that’s my next venture.

 

 

Mel

 

 

Modeling the SP in HO scale since 1951

 

My Model Railroad   

http://melvineperry.blogspot.com/

 

Bakersfield, California

[RR_Mel]

Randy

 

I finally gave up on the 5mm RGB LEDs.  The color out of the RGB LEDs is much better then anything else I’ve tried, but the 5mm diameter is just too large for HO scale.   Reducing the diameter of the top of the LED works OK but the back or terminal end can’t be reduced enough to look even close to scale.  5mm may be only a foot and a half in HO scale but it looks really bad compared the 3mm LEDs on the back side of my signal heads.

 

The RR-CirKits work good but they don’t look as good inside the heads without a lens as the 3mm bi-color diodes.  I had all 32 heads installed and operating when I started the RGB thing and quite frankly it isn’t worth the money or time to change out to the RR-CirKits LEDs.

 

The small amount of off angle red and green wouldn’t work for a rivet counter but I’m not one so I’ll live with it.  I’ve never had a comment from a visitor on the slight off angle colors either, only OOO and AH AH AH or “did you see that” as they change colors.

 

Thanks again for putting me on to RR-CirKits, because of their small size I’m positive I’ll put them to use somewhere on my layout.

 

Mel

 

 

Modeling the SP in HO scale since 1951

 

My Model Railroad   

http://melvineperry.blogspot.com/

 

Bakersfield, California