led circuits

[Anonymous]

who out there has experience with led circuit diaghrams for loco lights, I have several Athearn diesels and a would like to add working head and ditch lights but don't know how can anybody help?

[Anonymous]

Hi Phillip
I don't know what scale you model or if you are using DCC or DC, however I found and have used a very small voltage regulator from Digi-Key ( http://www.digikey.com ) part #TK11625CT-ND (100 mA, 2.5 volt output). Absolute maximum input votage is 16 volts. Most HO scale DC systems are about 14 volt.
You will need to connect the voltage regulator to a bridge rectifier, part # DF02MGI-ND.
The voltage regulators are in a TO-92 package. With the flat side facing up and the pins pointing to you, the right pin (#1) is the positive (+) output. The center pin (#2) is common ( - ) and the left pin (#3) is the positive (+) input voltage. The bridge rectifier is connected between the motor, or any voltage pick up point, and the voltage regulator.
Both leads from the power pick up connect to either pin marked ~ on the bridge rectifier. The + pin on the bridge connects to pin # 3 (+ input) on the voltage regulator. The pin marked - on the bridge rectifier connects to pin #2 (common) of the voltage regulator. Pin #1(+ output) of the voltage regulator connects to the anode ( long pin) of the L.E.D. and the cathode (short pin) connects to pin #2 (common) of the voltage regulator.
Total cost per unit is about $2.20 less L.E.D.s and wire and printed circut board (optional).

Of course if you are using DCC, forget the above and just use a resistor connected to the wire for the headlight on the decoder. To calculate the value for resistor subtract the L.E.D. voltage from the track voltage and divide that by the current draw (in milliamps).

The formula is written as V in - V led
........................................I led .....................

G.
p.s.
To prevent a short curcuit, cover all exposed terminals with heat shrink tubing or liquid tape after you test the curcuit.
Remember, anything that uses electricity generates heat to some degree. Therefore keep components away from any plastic in the locomotive.

[nfmisso]

E-mail me for a couple of circuits and sources.

[Anonymous]

Use a resistor. To figure out the resistance you need use Ohms law (Everyone need to know this if they do any electronic work).

V = I*R

Also written as -

R = V / I

R is resistance.

V is voltage drop needed. You can calculate this by taking the track voltage minus the voltage rating on the LED. For example, if your track voltage is 14 volts, and you LED is rated for 2 volts, you need a voltage drop of 12 volts.

I is current. Don't ask me why they use I, although there is probably a reason. This is the current rating on you LED. If your LED is rated in milliamps, divide the rating by 1000 to get the value in amps. (Do the same if the voltage is in millivolts.)

[cacole]

Instead of going to the expense of a voltage regulator, which may require a heat sink, you could use a small bridge rectifier with the AC terminals connected to the track power and the DC output terminals connected to the LED through a 1,000 Ohm resistor, being sure that you get the polarity correct. Unless you have several locomotives that you want to modify, you will have to pay more for shipping from DigiKey than the rectifier and resistors cost, so check for a local electronics store.

[Anonymous]

You may also be able to get a complete LED setup, including circuit board, from RamTrack. I believe you would want the 3mm LEDs for the Athearns. I made the mistake of buying the 5mm, and it doesn't fit. Installation is straightforward, connect the leads to the pickups and you're in. The circuit board contains the necessary rectification as well as current dampening (via resistors). I believe they run about $15.00 or so.

[Anonymous]

QUOTE: Originally posted by cacole

Instead of going to the expense of a voltage regulator, which may require a heat sink, you could use a small bridge rectifier with the AC terminals connected to the track power and the DC output terminals connected to the LED through a 1,000 Ohm resistor, being sure that you get the polarity correct. Unless you have several locomotives that you want to modify, you will have to pay more for shipping from DigiKey than the rectifier and resistors cost, so check for a local electronics store.

Just a note to say Digi-Key drops the $5 handling charge for orders over $25 (U.S.) and they can ship orders 8 ounces and under via U.S.P.S.

A resistor will also work but if you're using DC power, you won't have constant brightness untill the track reaches full voltage. In other words, the resistor will drop the track voltage at all voltage levels and the light will not light untill the track reaches full voltage. A regulator will reduce track voltage from 2.5 volts on up and will light a bulb or L.E.D. when the track reaches 2.5 volts.
Also a resistor will still get as hot as the small regulators. Unless you put too much voltage or overload them, the regulators don't get so hot as to melt plastic or burn you, but they do get warm.
I like to add, if you do use resistors, buy resistors rated1/2 watt or more.

G.

[nfmisso]

QUOTE: Originally posted by cacole

Instead of going to the expense of a voltage regulator,...... you could use a small bridge rectifier

The above information is not correct, a bridge rectifier is going to run $0.50 in small quantities, where as an adjustable regulator runs $0.40 in small quantities; plus $6 S&H so plan your purchases, get the other components at the same time.
See:
http://www.allelectronics.com/cgi-bin/category.cgi?category=110&type=store
http://www.allelectronics.com/cgi-bin/category.cgi