Yes, there are tutorials.
Just Google, LED tutorial.
I will assume, for DCC so search for led dcc tutorial.
Just in case you don't search, the below fellow has lots of info.
http://www.members.optusnet.com.au/nswmn1/Lights_in_DCC.htm
Generally a 1k resistor is used for a single 20 ma LED's but with high output LED's the resistance has to be quite higher but for most, 1k, 1/4 watt is normal.
Store links in Favorites.
Rich
If you ever fall over in public, pick yourself up and say “sorry it’s been a while since I inhabited a body.” And just walk away.
This has always been a very handy picture for me when wiring LEDs up to decoders:
The blue (common) wire is always attached to the anode (+); the yellow & white wires are always attached to the cathode (-). If you look inside the LED bulb the cathode leadframe is always the larger of the two. Another identification mark is the flat spot on the cathode side.
While an LED is a diode and current can only travel through it in one direction, a needed resistor can be soldered to either the anode or cathode.
Tom
https://tstage9.wixsite.com/nyc-modeling
Time...It marches on...without ever turning around to see if anyone is even keeping in step.
Do you have a particular application for LED's? They are used everywhere.
All the light bulbs are LED types in my house.
I built a bicolor red/green signal system for our club some years ago that used five VDC logic and a lower resistance.
The NCE Power Cab uses a red LED and 1k resistor to monitor the DCC output. No diode.
Christmas trees loaded with LED's and operate off of mains power.
ndbprr:
As was suggested, tell us what you want to do with the LEDs and we can give you more focused responses.
Dave
I'm just a dude with a bad back having a lot of fun with model trains, and finally building a layout!
An LED is NOT a light bulb. It is more like a rectifyer. It does not consume electricity, it just passes it through albeit with a minute drop in voltage.
But it is very sensitive to current. You need a resistor to cut it down to a safe level. With the correct resistor a common LED will operate on 3 volts to 20 volts or more.
LIONS simply use 1K Ohm resistors on 12 volts, signals operate on 16 volts.
Do not wire LEDs in series. They will work (without a resistor) but not for long.
ROAR
The Route of the Broadway Lion The Largest Subway Layout in North Dakota.
Here there be cats. LIONS with CAMERAS
There are two basic things to know about LEDs.
1. They are polarized. They only work hooked up the right way. + and - matter, unlike a light bulb.
2. LEDs are current devices. The voltage does not matter, the current does. A light bulb gets brighter as the voltage rises, until you exceed the rating and it burns out. An LED tends to get brighter as the current rises, until you exceed the maximum and it burns out - though an LED burning out can be literally explosive as it blows a small chunk out of the epoxy coating. Light bulbs have a rated current they draw, voltage is what varies. LEDs have a rated voltage they drop, the current is what varies.
Combine those two facts with Ohm's Laws and Kirchoff's Laws (many tutorials on this exist although the Kirchoff ones may get overcomplicated as they discuss nodal analysis (forget I said that, you don't need to know what that means) - so search one of my old posts where I've explained it (I need to copy that and just put it on my web page) for a basic circuit of a power source, LED, and dropping resistor.
And also apply the one thing common to most anything electrical./electronic - unless you have a really darn good reason, never run any component at its maximum rating. The numbers on the datasheet are typical (typ) or maximim (max). The variable parameter (in the case of an LED, the current) is usually specified as a max. For most common white LEDs, this is often 20ma. Following what I said - you do NOT want to design the circuit so the LED runs at 20ma. Just like you do not want to load a 12V 1 amp power supply to a full 1 amp constantly. Leave a 75-80% margin - when it comes to LEDs, often even more of a margin to get a pleasing light level - remember, more current = brighter, less current = dimmer. For regular size white LEDs used as headlights, the oft-quotes 1K resistor connected to a typical decoder results in about 9ma through the LED - that's less than HALF the rating, but is plenty bright. Bigger resistor = less current, and in the case of many of the high efficiency surface mount types you might use for exterior lights on a structure or ditch lights on a loco - even 9ma is too much, not in a possible component damage sense, but in a "way too bright" sense - so you would use a bigger resistor for less current to tone down the LED brightness.
That pretty much covers it, really.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
For many years I have usually run electronics at about fifty percent. With diodes, that is about 10 ma.
Having worked in electronics for many years I have a 2.5 k pot, assortment of resistors, 12 vdc supply and clip leads for figuring values.
If you are good at math, you probably will not need test equipment such as a multimeter.
A couple years ago some fellows in a couple Yahoo DCC forums picked up LED testers shipped from China free. As I recall, the device was a few dollars and worked quite well.
On ebay. Most stuff we buy today is from China.
Current and brighness determination.
Simple LED tester...
Get one of those 2-battery AA or AAA battery holders. Radio Shack MAY still carry them, but are commonly available. Attach a black lead to the negative output. Build a red lead with a piece of wire and a 1k ohm resistor, attach to positive output.
Touch to the LED, + to + and - to - to test.
A set of clips on the leads is somewhat fancier and may be useful. I just touch them to the LED in question.
Mike Lehman
Urbana, IL
richg1998If you are good at math, you probably will not need test equipment such as a multimeter.
My approach is that you need about 570 to 600 ohms to protect the LED on 12 volts, then anything extra is to dim to suit the application. I use over 100 K ohm sometimes, but for loco headlights 2k is good unless you have a modern diesel, which tend to be more intense.
I just do it now based on experience. Used to be a little more uptight about calculating, but observed the results and pretty much do it by eye and hunch now.
Also, run them on less than 12 volts and you need even less. I have lots of buildings on 3.5 to 4.5 volt supplies. I often use a single 10 ohm resistor for a building with multiple LEDs. No failures. I recently experiemented by doing a structure with a dozen LEDs without resistance except for what was in the wiring itself on one of the 3.5 v circuits. It's a little brighter than others nearby and intentionally so, which is why I decided to experiment. Still running fine after a month,on 12 hrs/day average on time.
ndbprrIs there an LED tutorial somewhere on the internet?
LED circuit
greg - Philadelphia & Reading / Reading
http://trainelectronics.com/LED_Articles_2007/LED_104/index.htm
Made the link clickable.
I didn't know such things existed!
Thanks
Constant current drivers of all sorts have been around for years now, single chips and slightly more complex ones made up with individual transistors. Such things are critical where the voltage can and does vary - say a good quality flashlight, thus the light stays at the same brightness throughout the life of the battery. Or in a car, where your voltage can drop to 12V or less with a weak battery but once the engine is running you can get close to 14V. Or to use an LED with DC powered trains - there really isn't a decent resistor that keeps the LED at a reasonable current from 3 to 12 volts, but a constant current circuit can keep the LED at the proper level no matter how fast you go. Or as a couple of posts up - a fixed voltage driving all accessories and building lights, some with 2 LEDs, some with 5 LEDs or more - just throw that inexpensive constant current chip in there and you won't have to worry about calculating resistors depending on how many LEDs you equip a building with.
Randy:
Thanks for the explanation. I just ordered some.
I have what may be a dumb question. The output from the LED driver is 20 ma which will make the LEDs quite bright. Can I use a resistor in series to dim the LED(s)? I'm thinking of cases where I'm using three or four LEDs in series in structure lighting.
For a 20ma current source use 2 LEDs in parallel for 10ma each, or 4 in parallel for 5ma each. All must be the same type though so they split the current approximately evenly - don't mix and match a regular 3mm LED with a high efficiency SMT LED, for example. A small resistor, like 10 ohms, on each one can help even out the current distribution among the parallel LEDs if it is an issue and some are much brighter than others.
A series resistor won;t work like it will with a voltage source. Kirchoff's Laws, 2 devices in series have the same current flowing through them, so you put say a 1K resistor in series with an LED powered by a 20ma constant current source, the resistor will pass 20ma and the LED will pass 20ma. The resistor will have a voltage drop E=IR, or 1000 x .020 = 20V so unless the voltage is > 20V + Vf of the LED, it will just not light up. Even with a smaller resistor, it just drops less voltage, it does not reduce the current through the LED. That is the downside of the contant current sources for LEDs, often they are made for applications like flashlights or LED replacement lights where you want the maximum brightness, thus the common 20ma output - you'll find them in the better LED replacement bulbs (cheap ones use a capacitor dropper (for AC, a capacitor can drop voltage like a resistor does for DC), a rectifier, current limit resistor, and a whole bunch of LEDs in series to add up to say 100V worth, with the resistor handling the extra). Check out bigclivedotcom on eBay, he does teardowns of various LED repalcement lights among other things so you can see what's inside a lot of that stuff. Plus his day job is theatrical lighting/sfx and he often has behind the scenes footage of the various lighting and effects devices. And some downright silly stuff, like the time he and his crew made popcorn in a PAR can - a theatrical spot gets MORE than hot enough to boil oil in which to pop popcorn!
So it wasn't a dumb question! Just the person asking it.
Thanks for the explanation. I think I understand the issue with using resistors and LED drivers together. Putting two or more LEDs in parallel is certainly easy to do.
Your knowledge is much appreciated!
Cheers!
You'd be surprised at how much some of this is new to me. Yes, it applies concepts I learned 30 years ago, but unless I have one on hand (and I don't think I do), you will almost certainly build an LED circuit using a constant current source before I do - my degree is in electrical engineering but I never actually worked as an EE, what little I did do goes back to just the first year after I graduated in 1988. After that - electronics is just a hobby foir me, and mostly all digital at that, and I've been a computer guy. I managed to pick up a collection of electronic magazines from 200 to present, I'm up to 2007 now, so I am aware of many of the newer things out there - plus things like Dave Jones' EEVBLOG Youtube channel has lots of good info, his fundamentals stuff turned the light bulb back on and wouldn't be bad for someone trying to learn - if you can take his voice. Doesn't bother me, but he's a small Aussie guy so in addition to the accent his voice is somewhat high pitched. My GF thinks his voice sounds like nails scraping on a chalk board and leaves the room if I watch one of his videos.
I had a quick look at Dave Jones' videos. Very entertaining but I think I would be exhausted if I watched more than a few minutes at a time! Most of his stuff seems to be way beyond what I need to know, or want to know.
Yeah, he is all over the place, from fundamental stuff to advanced topics. The Mailbag segments are fun, people send him all sorts of crazy stuff. Lots of fun when he has his kid on with him/ Pretty amazing that he started with a workbench in his garage while he still had a regular dya job and now owns space in two different buildings with a huge lab and an office. Oh, look up the ones on the Indiana Jones train set for model railroad content - he's a bit of a model railroader as well. Seems a hobby shop near him closed up and since he's both a train buff and an Indiana Jones fan (and a HUGE Back to the Future fan), he managed to get them to let him take the layout so long as he could remoove it from the property. Kind of a simplistic waterwings plan but it has scenese from all the Indiana Jones movies including lots of lights and animations - like mine carts from the second one, the big flying wing fight with the giant German guy from the first one, etc.There are a couple of older videos where he goes over it trying to figure out how he can take it apart to fit in a van, then there's one where he cuts it apart, and there's a more recent one where he started putting it back together again (only a few year have elapsed LOL. ) He also has a second YouTube channel, EEVBLOG2, where he posts stuff not necessarily of interest to electronics people, and he has several videos there of riding various tourist rail lines in Australia (and one of a huge G scale layout). And being so into science he managed to convince his wife to name their first boy Sagan, and he has a little brother Huxley. Sagan loves trains too. There was another video from about 2 years ago or so, he has a small N scale layout he kept int he lab, one of those pre-formed base things, and he pulled it down and got it running with Sagan.
Paul D
N scale Washita and Santa Fe RailroadSouthern Oklahoma circa late 70's
Sure. You could even get something like a 5,000 ohm potentiometer and insert in the circuit on a temporary basis. Adjust the potentiometer until you get the desired brightness, then disconnect it and measure the value of the pot. Replace the pot with a fixed resistor with a value close to that which you measured.
By the way, while you can do the same thing with a plain LED without an inbuilt resistor, it is very risky since it would be easy to run the pot down to too low a value and blow the LED.
PEDI have a bunch of LED with resister already built into the wiring. However, the LED is much brighter than I desire. Can I insert another resister in series with the existing LED/resister to make the LED dimmer?
Yes you can.
I keep a 2.5 k potentiometer on hand with a 12 vdc supply for establishing LED brightness. Start out and max on the pot.
Been working in electronics for many years and have a well stocked junk box for experimenting. One quarter watt resistors are just fine.
There are super bright LED's that might require a lot more resistance.
Knowing that you are starting with a 12V supply, you could add a fixed resistor so that if the por were accidently turned to minumim it wouldn;t fry the LED, Rarely for hobby use are LEDs too dim, witness all the extra added to dim them down when a 1K resistor is already less than half the LED's current rating. The final answer would then be the fixed resistor plus the pot reading, instead of just the pot reading with the added bonus of not blowing up the LED because the pot was turned too low.
And it does happen, the other day I wondered why my circuit wasn;t working - I previously had set the current limit on my power supply to a fairly low value, something to protect the previous circuit I was working on, and neglected to turn it back up. The new circuit drew more current, so it was putting the power suppyl into current limit mode and the voltage was dropping well below 5 volts. Though I always try to remember to at least turn the voltage down when shutting things off, I always turn on the power supply with it disconnected from the circuit just in case - wouldn;t do to feed 12V into a 5V chip with an absolute maximum of 5.3V.