When I got back into the hobby, I decided to start with T-Trak.
That lead me to discover a problem or two
The first is that I could NOT rely on what power I’d have for accessories. Some folks bring their own power, there are two standards for the accessory bus, and some folks power off one loop or the other, and that can be DC or DCC. Obviously with DC the voltage varies. It is even more fun if you are putting lighting in rolling stock.
The other was that so many club members get confused about what dropping resistors they need. It varies based upon voltage in, and what is known as Vf of the LED (for all intents color)
The confusion comes from the fact that LEDs are really current devices, not voltage. You want some constant current below the maximum.
So I designed a little circuit that will give you a constant current. Right now you have a choice of 1.7 and 2.3mA. As a side effect, I discovered it acts as an about 1 second keep alive for going over switches and the like.
It’ll take 5v to 30v AC, DC, even DCC, and drive at constant brightness. Below 5 volts, depending on the color of the LED, it may dim (white will get down to about 5, red down to about 2)
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