# Signal colors.



## John J (Dec 29, 2007)

Any one know about signal colors. Do they use Yellow much?

I am looking for Tri Color LEDs. but only can find Red, Green , and Blue.

Do they use Yellow for anything/

JJ


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## toddalin (Jan 4, 2008)

In the right intensities, red and green make yellow.


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## Garratt (Sep 15, 2012)

Red Green and Blue are the primary additive colors therefore any color can be made from mixing them together in the correct proportions.
For an amber you need a little less green. Below link has a calculator to give you some mixing examples. Change it to RGB mode. The result mix is in the 3 hexadecimal values grouped as one. Pure white is FFFFFF.

http://www.sessions.edu/color-calculator










Andrew


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## Garratt (Sep 15, 2012)

Yellow is used for caution in distant signals in Australia.

Andrew


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## krs (Feb 29, 2008)

Most places tell you to use a bi-clour red/green LED and apply AC to get some sort of yellow.

But they also make three chip - R/Y/G LEDs, they are just not very common and probably hard to get and expensive.
http://www.bivar.com/portals/0/products/SMP4-RGY.pdf

What did you want to use the LED for?

Knut


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## toddalin (Jan 4, 2008)

It's fairly easy to get a signal to cycle from green to yellow to red using a green/red common anode LED, a cheap relay, a capacitor, and a resistor.


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## John J (Dec 29, 2007)

krs said:


> Most places tell you to use a bi-clour red/green LED and apply AC to get some sort of yellow.
> 
> But they also make three chip - R/Y/G LEDs, they are just not very common and probably hard to get and expensive.
> http://www.bivar.com/portals/0/products/SMP4-RGY.pdf
> ...


Signal tower along side the track. 

JJ


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## Greg Elmassian (Jan 3, 2008)

I would use a 3 wire red/green led, and fire both red and green for your yellow.

The bicolor led, usually means bipolar, which is only 2 leads, and you would have to use AC to get yellow... too much trouble in this instance I believe. You run battery power right? 

Greg


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## SD90WLMT (Feb 16, 2010)

JJ, the three lite track signals here...run yellow - caution - in between all Red to Green tranisitions..
I see yellow quite alot...a train has passed...and traveled some distance, but is still not clear.. or far enough ahead of the trailing train to show Green yet... if it is too long .. the lites just go out...till a train is 1 mile from a signal out in front... then I'll see Green...waiting for a train to show.

Dirk


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## CliffyJ (Apr 29, 2009)

Here's an R-G-Y unit, but they cheat and use 3 discrete led's. So fwiw,
http://www.jameco.com/Jameco/Products/ProdDS/1717185.pdf


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## Garratt (Sep 15, 2012)

This link shows the two types Greg mentioned.
The two wire unit goes red or green depending on polarity of the power and with AC power both red and green will cycle with the AC current. They persistence of the eye will mix the two colors to see yellow. 

As Greg said, the 3 wire version would be easier to use in a simple circuit where AC may not be available. Both red and green need to be lit for yellow.

http://www.learningaboutelectronics.com/Articles/Tri-color-LED 

Andrew


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