L.E.D.s

[Anonymous]

Im putting an L.E.D. FRED in a car. Just to be sure... What lead do you put the resistor on. And will it work on DCC? im just running it off track power.
And does it matter which polarity goes to which lead? if so. How can i take the track power and make it just one polarity all the time inside the circuit?

[cacole]

It does not matter which lead gets the resistor. Yes, an LED will work just fine with DCC. Polarity is critical on an LED or it won't work at all. Look at the leads on the LED. The longer lead is the positive, and must always have positive current to work properly. For track power, you must also put a bridge rectifier into the circuit that will feed the correct polarity to the LED. You're also going to need a circuit to make the LED flash on and off to represent a FRED, unless you have one of the LEDs with a built-in flashing circuit.

Since an LED draws such a small current, you can use an integrated circuit bridge rectifier. I don't remember the exact model number, but I purchased a bunch of them in bulk a few years ago from All Electronics that are round, and smaller in diameter than a dime. A bridge has four leads. Two have an AC symbol on them, and the other two are marked as + and -. The AC leads go to the track pickups, and the + and - leads connect to the LED.

When I built a FRED for the back of my double-stack container train, I just put a AA battery under the rear container wired through a small on/off switch, and used a self-flashing 3mm red LED. I have seen some FRED circuits that use small wrist watch batteries.

In order to use track power, you're going to need pickup wipers on the rolling stock, and that can be difficult to do. Consider using a battery instead, and avoid all of the additional modification and electronics.

[Anonymous]

I already have the wheel pickups. I wired it without a rectifier last night and youre right. it only runs on one polarity. I am using one with a flasher circuit built in, but it flashes too fast for my taste. How can i slow it down?

[rrinker]

Typically, the LEDs with built-in flashers are not adjustable as to the flash rate.

Here is a page with a simple circuit for a FRED flasher that runs off DCC track power: http://home.cogeco.ca/~rpaisley4/FredDCC.html

--Randy