Thanks for the quick response, ROAR, For the fun of it, I will rummage around here for an obsolete, but suitable wall wart, do some soldering with 1000 ohm resistors, following your earlier directions, connecting the short lead (cathode) and resistor to ground and longer lead (annode) to power. Will report my success!
For information or curiosity sake, I would still like to learn what the circuity and component specifications would be for a 5v -19v Universal AC/DC hookup, if someone could tell me.
Thanks again, swede
rrswedeI am no electronics or electrical craftsman but can reason and follow instructions. I have 50 ea. 3.3 volt 0.066 watt LED lamps from an extra Christmas string rated at 3.2 watts and 0.027 amps that I would love to play with. Is there a generic schematic that shows the correct placement of the various components necessary to wire an LED using variable AC and how do I determine the proper specifications for the components?
The 3.x volts is the minimum voltage needed to light the LED. Any voltage (3 - 20) will work just fine, but you MUST limit the current. The math mavens and electricl engineers will tell you exactly what resistor goes with your circuit, but the LION does not care. You can use a DC wall wart and it will light 100s of LEDs, just put a 1000 ohm resistor in series with each LED and you are good to go.
The LION has many circuits on the layout of him, all of them use a common ground, grounded to the building system. With out a good ground you would have all kinds of stray voltages on your common circuit.
So run the negative circuit around your layout, and ground it. Connect the positive circuit to your LEDs and you are good to go. (Remember the story of the Annode and the Cathode).
ROAR
The Route of the Broadway Lion The Largest Subway Layout in North Dakota.
Here there be cats. LIONS with CAMERAS
Like CNWman, I am new to this forum but frequently visit the Classic Toy Train Forum since my interest is in prewar O guage railroading using AC as my power source. I came to your post (ROAR) while searching for info regarding the use of LEDs and thoroughly enjoyed studying your response to CNWman. The following is a copy of a post I placed on the CTT forum yesterday. I have not had a response and knowing DC is the power source typically used by members of this forum, was reluctant to post here. However, nothing ventured, nothing gained, so here is the post and perhaps you or another member can assist me.
For some time I have considered incorporating LED lighting in my layout. I have seen after market offerings for LEDs operating between 5 -19 VDC, prewired universally for AC or DC power sources, (http://www.modeltrainsoftware.com/bl-212.html). The circuitry includes bridge rectifier, capacitor, resistor and lamp and I have been tempted to make a purchase. However, I would rather learn something in the process as opposed to simply hooking up a finished product. I am no electronics or electrical craftsman but can reason and follow instructions. I have 50 ea. 3.3 volt 0.066 watt LED lamps from an extra Christmas string rated at 3.2 watts and 0.027 amps that I would love to play with. Is there a generic schematic that shows the correct placement of the various components necessary to wire an LED using variable AC and how do I determine the proper specifications for the components?
Thanks for your input,
swede
WOW.. .thanks so much for the tutorial. I copied it and will refer back to it when I get that far on my layout. I work at Home Depot and bought a bunch of the Christmas LED light sets at phenominal savings. Thanks everyone for your input! I think I'm going to like this forum.
You don't need a book.
Everything you need to know can be found on the Internet.
Just Google for what you are searching for.
And ask questions here on the forum as issues arise.
That is honestly the best way to approach this subject.
Rich
Alton Junction
An LED tester is a very handy tool to have if you are going to play around with LEDs.
I can not find the same type that I bought years ago at Micro-mark but it clips to a 9v. battery and has two mini-grippers. I like this style because I use a lot of "axial" LEDs for signals and I can check them without bending the leads.
There is this type as well and the nice thing here is you can check the brightness against varying current.
http://www.ebay.com/sch/i.html?_from=R40&_trksid=p2053587.m570.l1313.TR4.TRC2.A0.H0.Xled+tester&_nkw=led+tester&_sacat=0
I have hundreds of LEDs around and many are the "water-clear" variety and the only way to know the color is to light it up.
Of course, you can make your own LED tester but some of the ones available out there are SO cheap it's almost a waste of time.
Buy a few assorted bags of cheap LEDs and start experimenting (many sellers throw in 1K resistors, a handy rating to use with most LEDs at 12v)
LION pretty much covered everything you need to get started...
Have FUN, Ed
Lion wrote you a treatise, but in case he missed anything here are a couple of more useful links:
http://www.trainweb.org/girr/tips/tips7/white_led_tips.html
http://www.trainelectronics.com/articles.htm
http://www.spookshow.net/lowvcircuit.html
Mike Lehman
Urbana, IL
NOPE. No good books. LED lighting such as we do it is a very nitche subject, and so I am sure that there are no really good books for you to read. Or if you do find one it will be so technical as to be of no use to you.
The premise is simple howerver, and so I will tell it to you.
The LED is first of all a DIODE, a light emitting diode. It will pass current in one direction, but not in the other. So Think of a rectifier instead of a light bulb. It passes electricity, it does not consume it.
Light bulbs increase their brightness the more voltage you apply to the circuit. Too much voltage and the thing burns out in a flash.
LEDs are different. They may require 2 or 3 volts dc to light it, but if the current is too high (and it is) you will burn it out instantly. So ANY VOLTAGE between 3 and 24 volts will work just fine, but you MUST put a resistor in series with the device to limit the current. While they do act like rectifiers, passing voltage in one direction only, they really cannot be used as a rectifier since a revers current can also kill it.
The LED above is a T1 (a convention used by the lighting industry... it means a tubular shape 1/8th inch in diameter... it says nothing about the electrical characteristics of the lamp.) Most LED manufactures will now call it a 3mm LED. The Larger size is a T1.5 or 5mm.
Looking again at this LED you will see that it has a large flag inside of it (left) a small gap, and then a small flag. If you were to look at it from the top you would see the actual LED element resting on top of that large flag as if in a little frying pan. The Large flag is the cathode, the negative pole of the LED, and it has the shorter lead coming from the device. The smaller flag then is the annode, is positive, and has the longer lead.
LEDs that you are likely to use have either a rounded top which acts like a spot light, or a flat or more properly an inverted cone shape to the top which spreads the light out more like a flood light.
LEDs can be purchased from electronics dealers at about 10c for colored lamps or 70c each for clear lamps. Of the clear lamps there can be "Warm White" or "Cool White". The cool white do well to emulate mercury or flourscent lights, while the warm white do well to emulate an incandescent light source.
There are those here who are master engineers, electricians, and mathamtacians, who can tell you how to compute the size resistor that you will need to use for a particular LED, since all LEDs have their own complex specifications. However the LION ignores all of that complicated stuff. Use 12 volts DC as I have explained and use a 1000 ohm 1/4 watt resistor. Actually an 1/8 watt or even smaller resister will work just fine, but the 1/4 watt resistors are FAR cheaper. LION buys them by the thousand for $12.00. (All Electronics, an MR advertizer)
But... LIONS do not pay that much money, and if you are lucky you can go out right now, and buy up bunches of Christmas LED sets at the big box stores. Run Run Run, before the LION buys them all up and you be left with your hands in your pockets.
You will find sets with the 5mm lamps seated by themselves. For HO scale, I like the 3mm lamps much better, the ones with the plastic do-dads on the tops of them have the smaller 3mm LED inside. They are dificult to take apart because the maker does not expect you to open them up. After pulling the lamp out of the string, you will need to hold the plastic base in on tool, and grasp the cover with another tool to pull or break the lamp open. Unbend the leads and the LED will drop right out. LION cuts the leads even shorter, so you will need to know the cathode from the annode without the lenghth of the wires giving the show away. BIG flag = Negative. LION puts the resistor on the negative pole, just to be uniform about things, and then always connects this one to ground. The other wire may be connected to the power source. LION likes the resistor in the same proximity as the LED so that he can see it there and know that his circuit is protected.
As a bonus, look at your set of Christmas lamps. The lamp holders are all on one wire, and the other two wires pass by uninterupted. So... on a 35' set of lamps, the LION recovers 70' of nice heavy hookup wire. Wire is so expensive that all of this free wire is a big deal.
Here is a run of LEDs built into the passenger platform of the Prospect Park station on the Layout of the LION. (LION modes SUBWAY trains). Atop each row of pillars a bare copper wire is strung ground on one side, and hotel power on the other. The lamps and resistors are soldered to these bus wires, connected to the power, and a platform roof covers the whole works.
LEDs are really very forgiving devices (except if you kill them with too much current.) They will work in series but do not be tempted to do that, wire each one in parallel with its own resistor, and it will live virtually forever.
On this signal application, I have tied the cathodes together and will use only one resistor since only one LED will be illuminated at a time.
Signals on the subway have no targets around them as they are not necessary in a tunnel, and clearences are not that great.
My lamps should be closer together, but the wooden mast cannot survice that strain. This is a 3' railroad. It is best viewed from 3' away.
And now, without spending a dime on a book, you know all there is to know about LEDs from a model railroaders point of view.
Hi, I'm new to the site. Can anyone suggest a good book on the use of LEDs in an HO scale layout (mostly related to scenery such as signals, structure lighting, etc.)?