# Bi-polar LED White/Red?



## krs (Feb 29, 2008)

This subject really fits into any of the power and sound forums other than the sound one.
I placed it into the DCC section since people here are most likely to work with LEDs.


Does anyone offer a bi-polar LED that provides white and red as colours rather than the traditional red/green or red/blue. 

I couldn't find one in either 3 or 5mm, 10mm is too large.

And as a supplementary question, has anyone ever tried using a RGB LED in that mode - theoretically driving all three colours should provide white light and the "R" by itself obviously red light.

Thanks,

Knut


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## pinewoods (Jan 20, 2009)

I have never seen a white/red LED. A while back I tried to do searchlight signals (red, amber, blue-green) with RGB LEDs and have never been real happy with the results. A diffuser or fesnel lens helps to blend the colors together better. Some newer LEDs are much brighter but I have not tried any of those parts. I used a little microcontroller to adjust the brightness of the individual colors but you could use different values of resistors as well. Have you considered using surface mount LEDs? Both a red and a white will fit in the space of a 3 mm LED. Solder them side-by-side with reversed polarity and make your own bipolar LED.


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## Greg Elmassian (Jan 3, 2008)

I seem to remember this question before.... and I seem to remember that they do exist. 

Google turned up nothing? 

Greg 

update: google "bicolor red white led"

3mm and 5mm about 60 cents each..


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## rmcintir (Apr 24, 2009)

Never ordered anything from these guys but found these 3 wire Bi-Color LEDS (not 2 wire): 

3mm red/white 
http://www.unique-leds.com/index.php?target=products&product_id=1972 

5mm red/white 
http://www.unique-leds.com/index.php?target=products&product_id=1973 

RGB LEDs are 4 wire devices so I thought this would still match.


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## Greg Elmassian (Jan 3, 2008)

That's the site! 

Greg


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## Axel Tillmann (Jan 10, 2008)

Knut,

I have a shipment of special Red/White LED coming which are special designed for DCC. As you might know, most 3 legged LEDs are common Minus (Cathode) and two individual Plus poles (Anodes). The LEDs coming in are common Anode and indivual Cathodes. This makes them universaly suitable. You can control them in your regular DC applications like the other types but also now in DCC.

These are the types I am getting:
3 mm green/red
3 mm white/red
5mm green/red
5mm white/red

Your choice


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## Tom Bray (Jan 20, 2009)

The ones at the link above have very impressive amounts of light but look at the viewing angle - it is only 30 - 40 degrees. That is pretty narrow. Many of the high output lamps have a viewing angle of 60 or more. It will make a great headlight but if you have to see it looking down from above you will want something that will defuse the light with a lens or something. 

Tom


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## bdp3wsy (Mar 14, 2008)

So how would you wire the red/white 3 leg led to work off track power of 18v so the light would show red going forward and white in reverse. Thanks Jake


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## Tom Bray (Jan 20, 2009)

I was thinking of doing something like that. I want to put something in the back of the F7s so that going forward they would be red and in reverse they would show white. The limited viewing angle might actually work to its advantage in that case. 

Tom


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## Greg Elmassian (Jan 3, 2008)

You use a common anode led... the anode connects to the DCC decoder common... then you hook (with dropping resistor) the red lead to the headlight wire, and the white lead to the rear light wire... just like 2 independent diodes. 

Regards, Greg


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## bdp3wsy (Mar 14, 2008)

Greg, for the engine how would you attach these to the QSI board. But can you use it in the observation car as the main rear marker light as red and change to white when you backup. Do you have any diagrams. Thanks Jake


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## Greg Elmassian (Jan 3, 2008)

Ummm... there are only 3 terminals on the led... hook the common anode (you will get a diagram or info with the led) to your DCC common (blue) (positive)... the other 2 leads are the "red" lead and the "white" lead... put a dropping resistor (you need to calculate) on each one, and connect them to the headlight and the backup light leads... seriously, if this is not clear, you run the risk of wrecking things even with a schematic... just read the above a few times. 

For a light in an observation car, you will want to use an inexpensive light decoder, the FL4 will work, about $14... has 4 outputs.. wire up the same way... I think the stock programming will be fine... 

Time to dig in and read the manual! 

Greg


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## pwiegner (Mar 9, 2008)

Hello,here in Germany I have a source for white/red LED with built in resistors. Look at www.bk-funktionsmodellbau.de and go to "Gartenbahn" and then to "Neuheiten" (new products). They work fine in DCC modus. I think Mr. Kurowski will ship to the US.

Peter


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