MARS/Gyralight lighting effects in P2K E7 : LUSENET : Wiring for DCC : One Thread

Hi Allan, I read your page on installing the above device. I have a Chief system and I'm installing a Soundtraxx DSD-150 in my E7A-B with four 1" speakers. I'm following your instructions pretty closely. Everything is going well, and the sound works, except I am confused about the lights. Doesn't the E7 have a gyralight and not a MARS light? I am confused since my E7 locos have an alternating headlight which I thought was a gyralight. I also thought that the MARS light was the orange rotating beacon on top of the cab. Bear in mind, however, that I have never actually used these special lighting effects before. Anyways, since you say it is a MARS light, it must be true! However, how do I replicate that function using only one lamp?


-- Jason Cameron (, January 28, 1999


The Proto 2000 box says it has a Mars light. The box also says this locomotive has a DCC plug. Mine didn't

A Mars light is a light that was mechanically swung from left to right. There was something similar to a Mars light that swung the light in a figure 8 pattern.

Forutnately, whether it is a Mars, gyralight, or whatever, you can model such a light with a single filament bulb. In order to understand this, you have to change your perspective. For one thing, you model train light will hardly throw and intense beam of light into the darkness. So you won't see the pattern any mechanized light would really have. That makes things simpler.

What you will see, in comparison to the prototype, is how the intensity of light would change to a viewer standing at one spot. Does it matter where the viewer is standing? No, not really. A rotating light will look the same to any viewer standing anywhere! The viewer will neglible light, then increasing brightness, a burst of bright, and then drop off and stay that way until the light comes around again.

The special effects functions of DCC decoders model the change in brightness that one would expect to see. It works amazingly well.

How do you use these functions? It varies between manufacturers. For the most part, you simply wire as shown for special functions. Frequently this includes a resistor as the Soundtraxx E7 installation does. Then program the special effects CV. My E7 installation includes those as well. Some of the special functions having varing rates to speed up/slow down the effect.

-- Allan Gartner (, January 31, 1999.

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