WHY DO I WANT ONE?
If you operate your trains without a caboose, then you’ll surely want to have a “Flashing Rear-End Device,” or FRED on the last car of the consist. Common among the prototype railroads, a FRED provides a bright red flashing indication that there’s a train ahead, and where the back of it is located.
HOW CAN I MAKE ONE?
The FRED design presented here is a simple, low-power circuit that closely approximates the real thing. The circuitry can be easily housed in a convenient boxcar or something similar. Several types of power supplies are shown, including simple replacable (non-rechargable) batteries, battery-less direct track operation, and more-sophisticated battery power which recharges from the track whenever possibly. Your size limitations, inventiveness and “DIY appetite” may determine which you choose. You may want to build the just the flasher itself and see how it works using 2 or 3 good-ol’ everyday AA alkaline batteries; this will help to quickly build your enthusiasm, and get your creative juices flowing. The few parts required are readily available at Radio Shack and others; you might want to build your FRED on a small piece of “perf board” (also from RS); I urge you to socket the IC, don’t install the IC until you’re all done soldering, and keep things as compact as possible. You’ll probably want the LED to be remote from the flasher circuit, so think about connecting to the LED with two wires twisted together. Keep in mind that LEDs are semiconductor devices, and are not fond of heat; hence, always use some sort of heat sink when soldering to LEDs and their ilk.
AND JUST HOW DO I POWER THIS THING?
This circuit will operate on as little as 2 volts (but you’ll want a bit more). A pair of rechargable Nickel-Metal Hydride (NiMH) batteries will produce 2.4 volts with long life. At this voltage, the flasher may be a bit dim for your tastes…or not. If you want a brighter flash, try going up to 3.6 volts; you’ll get this with 3 NiMH cells or any one of many special purpose disposable and rechargable battery packs (eg, cordless phone batteries). With only 2 batteries, I’d omit the LED resistor (47 ohms), and connect the LED directly to Vcc; with three batteries (or a 3.6 volt pack), leave the resistor in. If you want rechargable batteries, I recommend the NiMH units over NiCads; the NiMH batteries don’t have the “memory effect” that plagues NiCads. If you opt for rechargables, you have two choices for doing the recharging: in the train, or out of the train. That is, you can “trickle-charge” the batteries from the rail power, hopefully never needing to remove them from their hiding place in the boxcar; or, you can remove them when they run down, and insert them into a tabletop charger. If you remove for recharging, the electronics are simple — nothing but the flasher circuit and the batteries; the trickle-charge route is more complex initially, but should require no intervention once it’s set up. The charger circuits below are very simple and use readily-available parts (and tolerate substitutions readily).
1. Resistors are ¼ or ½ watt units unless otherwise specified.
2. 0.1 and 0.047 uf caps are 50V ceramic or film units.
3. Space permitting, AA size batteries may be used in place of AAAs; battery life will roughly double.
4. Substitutions for transistors or diodes may be freely made.
credits: Armadillo and Western