LEDs

This is a great series of articles, Bruce. Electronics is a mystery to me but your down to earth articles and sidebars make things much easier to understand. Keep up the great work.

Roy

Roy (Geared)

Thanks for the kind words.

I find that folks who want to can make things more difficult than they need be.

Yes, I got into a bit of semiconductor theory, but I feel that concepts help overall understanding. Once folks know which things determine what it is easier to realize what they can and can't control.

For example, if you have you have a DCC system with 14 volts on the track, you can count on 12 volts DC at the function outputs but not much more. If you are using white LEDs that fire at 3.2 volts, you can put three in series for 9.6 volts and calculate a dropping resistor to handle the 2.4 volts between the function voltage (12) and the sum of the LED voltages (9.6). BUT YOU CAN'T PUT FOUR IN SERIES! That would total 12.8 volts and you don't have enough voltage to fire them. There is nothing you can do to "fudge" it. They won't fire! Sorry. So, you put two in series and calculate the resistor for a 5.6 volt drop and put two more plus their resistor in parallel with the first pair. I'll be posting more about this on my web site (http://www.mrdccu.com/curriculum/Lighting/LED.htm).

Excellent job and very well written.

I have to comment that this article has been one of the better ones at making it very obvious and easy to tackle.  I have never played with LED's before but having read over this I feel I have the basic inforrmation to get started and be successful the first time out.

Thanks!. 

re: Excellent job and very well written

Glad you liked it.

Get some inexpensive LEDs and resistors - check eBay - and jump in!

Even if you destroy a few dollars worth along the way, it is a great education!

Error on page 41

There was an error that slipped through the editorial process.

Paragraph 5 in column 1 on page 41 was supposed to read:

"There are two major ways to connect an LED wrong: 1) reversed polarity or 2) without a series (current limiting) resistor. In the previous section we showed you how to determine the correct polarity and wire the LED accordingly. Now, lets talk about how to avoid the light show and smoked components that comes from driving too much current into a LED by having no resistor or too small of a resistor."

The text as published indicates that wiring a LED in reverse may destroy the LED or the decoder and that is TOTALLY INCORRECT. Check out the paragraph that begins with 2 in the LED THEORY sidebar on page 40.

Don't you just love proofing!

I can soooo relate to Charlie and Joe. Last week I received a company production that I pasted up. 132 pages of art and text. I proof read it like a hundred times, two of my colleagues proofed it, and the print house pre-press did a quick final proof.

Wouldn't you know it. I open the printed book and right on page 3 as plain as the nose on my face is a typo. How so many people missed it we will never know.

Thanks for the correction Bruce. I know exactly how the MRH staff feels.

DCC Impulses - Lights - LED Style

Another great article by Bruce.

I would appreciate Bruce also explaining viewing angles of LEDs. I have been caught out with LEDs in some of my control panels having too low a viewing angle. When viewing from above rather than near head on, it is difficult to see whether these low angle LEDs are lit or not.

Keep up the great work Bruce.

John Colliver

AUSTRALIA

Modelling Ogden Rails, Utah in 1953 in N Scale

viewing angles of LEDs

John -

That's beyond a DCC clinic.

Looks like you've covered it. If you are using a LED for a panel, you want as wide a viewing angle as possible. Need data from the manufacturer or dealer or a test sample.

Don't know what else I can add.

Now how to fix your panel. Have you tried a bit of light sandpaper? Rough up the lens a bit and you may be able to see it from a wider angle.

Good Reading

Another good read Bruce.

Regarding the Faller Expert Cement.  You mention it acts as an interface between the mating surfaces of the LED and the light pipe.  I'm interested in that aspect. 

I wonder if the Faller Expert Cement is OK for use with optic fiber or if it will melt the fiber like CA glue will?

Does anyone know of an MRH sponsor who stocks the Faller Cement?

Thanks.

Viewing Angle

In relation to John's question about viewing angle, I seem to recall an MRH article on LED lighting that touched on viewing angle to a degree.  Perhaps that article would shed some light on the issue of viewing angle?

I can't recall which issue it was off the top of my head though.

Edit: Thanks to Rod Goodwins Railroad Index, I found it easily!  It is in issue number 7 from May/June of 2010.

[Bruce's comment figure 7 on page 122 (http://issuu.com/mr-hobbyist/docs/mrh-2010-may-jun-ol/122?viewMode=presentation&mode=embed) probably tells folks a lot about angle. It shows 120 degree to 18 degree LEDs and the circle they illuminate.]

Lighting Structures With LED's - Lighting up the Night - pg 119

The author discusses viewing angle in a bit more depth.

using LEDs

Nice Article.   But.   There is an easier way to drive LEDs.   Try using Current Limiting Diodes (CLD) instead of the resistor.   Start with 20ma friendly LEDs and drop one or more behind a CLD.   It gets bright at around 4vDC and stays the same to 25vDC.   Headlights & Caboose lights no longer change brightness on DC layouts with the Throttle.

Add a CLD to the F0 output of a DCC Decoder and drive one, two or three LEDs in series with no sweat.

There are two CLDs on the Market.

Surface Mount = CLD20B [$.95ea] rated 4~45vDC

Thru-hole = CL2N3 [$.45ea] rated 5~95vDC

Both limit current to 20ma max. and are available at: http://www.mouser.com

[Bruce's comment - both limit current to 20 mA AVERAGE - 23 mA max. I'd be afraid to use these with any LED with less than a 30 mA maximum current rating. LEDs that inefficient are getting pretty hard to find.]

S

Current Limiting Diodes

Steve,

Thanks for the heads up on the current limiting diodes.

I know what I'll be adding to my next Mouser order.

Faller Expert

I've never seen it do so.

My former company, Litchfield Station.

Thanks Bruce!

Thanks for the feedback Bruce.

I'm off to get some glue.

THANK YOU BRUCE!

I have to say thanks for your column. I'm not much of an electronics guy but since I've begun reading your column I am feeling a lot more confident about starting those DCC / LED projects I have had in mind. Now all I need is to purchase the supplies.

Keep up the great work!

Thank You Thomas

Thomas -

Glad to help.

My advice - get extra parts and PLAY! You may destroy one! So what? Education does have a price.

You will notice that I'm working up to sound decoder installations. Stay with the less expensive ones for your early forays.

Great Service

Mr. Petrarca, you are doing a great service with your articles.  By making this subject easier to understand you enable those of us with "electro-phobia" to delve a bit deeper into lighting projects.  Thanks!

video clips are great addition

That, my friends, is why I'm writing for MRH.

Look for a full AV spectacular soon, a column based on my clinic "How Do I Get The Sound Out?" with audio and video clips!

I have been wanting to have a way to distribute that clinic to a larger audience since it first got rave reviews at NMRA national conventions starting in 2007. I've put the PowerPoint notes on my web site ( CLICK HERE), but without the AV support, it doesn't fly. Joe Fugate saw the clinic when I gave it in Anaheim in 2008. He and I agree that MRH is the best way to get the information to the most folks!

Yes, MRH is a great way to get the word out

Yes, MRH is a great way to get the word out. Our monthly audience is now in the 60,000's and growing steadily.

Bruce's marvelous clinic has only been seen by a several hundred modelers at most. I'm excited to see it will get a much larger exposure through MRH.

LED's

 I have been using LED's and SMD's for several years. They are the only lighting source that I use anymore. Your articles helped clear up some of the questions I still had about them. I look forward to future articles from you. Keep up the good work.

DCC Install in Older N-scale Steam

Bruce,

Great column as usual. 

Have you ever tried converting one of the old N-Scale Con-Cor 4-6-4 Hudson's to DCC with sound?

Thanks

DCC Install in Older N-scale Steam

Hello jmt99atsf -

I'm not an N-scaler. I've done some installations along the way, but I don't seek them out. I was blessed to have an employee when I owned Litchfield Station who had been in N-scale for decades. Jerry did almost all the N-scale sound after I hired him. He installed a Tsunami and two speakers in his Bachmann 2-6-6-2 after he rebuilt the drive train to fix a running issue. Not MY cup of tea! VBG

I believe he did a Hudson, but I cannot offer tips on that. If you would like to have him do something for you, you can eMail me and I'll forward it to him.

using LEDs

You are not looking in the right place then.Bruce. Try:

http://www.mouser.com

http://www.DigiKey.com

http://www.Jameco.com

http://www.Newark.com

http://www.Alliedelec.com

Yes, CLDs provide an average 20ma.   the LED gets 18 to 23 mA over a voltage swing of 4 to 25 volts.

Compare that to a resistor.  4 to 25v with a 540 ohm resistor [20mA at 12v] gives a current swing of 5mA to 44mA.   That is a significant brightness change.   If you are using a 30mA Max. LED you just ate it!  

If you use higher current rated LEDs then parallel the CLDs till you reach the mA you want.

I'll stick to using CLDs personally.

Steve

ps. watch the NMRA Magazine for an article on CLDs soon.

Different strokes . . .

Steve -

My grandmother had a saying, "It is a good thing that different folks like different things or every woman would be in love with my husband."

IMHO, a buck versus pennies is a big deal. For example, I'm currently working on a building that will have close to 100 LEDs in it. These are 10 mA LEDs that will be driven at about 7 mA, so CLEDs won't cut the mustard, either.

I am very glad that you found a way to use LEDs that satisfies you!