Can LEDs be used with SoundTraxx 'LC' decoders?

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IronBeltKen

Lazy Daydreamer
I just connected a Miniatronics YelloGlo LED [3-4vdc, with a 470-ohm resistor in series] to the headlight output wires on a SoundTraxx DSD-AT100LC decoder, applied power, and - zero, zip, nada! Tried both polarities, and forward and reverse. Still no light.

The SoundTraxx manual doesn't even mention LEDs in the troubleshooting section, only bulbs. But when I put a 12v bulb on there, it only glows orange, not very bright at all. There's got to be a better way...

I know many people are using LEDs with decoders, and they're not all electrical engineers either. What's the Secret Handshake? :confused:
 

NZRMac

In Training Down Under.
I've used 'em before with the LC. can't remember a secret society or anything just correct polarity, blue is common (positive I think) and yellow/white front and rear.

Ken.

Is the function 0 turned on!!:D :D
 

IronBeltKen

Lazy Daydreamer
I dunno Ken, if this is a secret handshake I'll bet the guys at Tony's Train Exchange know it. I bought this LED from a 'B-class' LHS (i.e. where trains are only 25% of their business) so I probably need a different brand.

BTW - this particular decoder didn't have any colored wires hanging from it. Just two little holes in the center on each end labeled, "connect bulb here" or something like that...
 
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RexHea

RAIL BENDER
TOP SECRET: From the journal's of Mr. Bourne
Ken, this a link to Soundtraxx manual for the LC. The top of page 10 says that the LC is not designed for LED's, but I think that means directly. I don't know why you couldn't hook it up using the same terminals as a reg bulb and using a resistor, unless the output of the decoder is not pure DC. That would explain what Soundtraxx says, "...an LED would glow dimly if at all." Your right that Tony's would have the answer.

You can check your LED just like a reg diode using an ohm meter except the forward bias direction will have more resistance.
If when you attach meter leads you read:
Infinity=LED is reversed bias
~14K+/- ohms=LED forward bias. (Good to go!)

When forward biased with meter your neg voltage should connect to the same LED lead as the black lead of the meter.

NOTE: If you check with meter and have infinity reading both ways of meter leads, you have popped it:eek: . Always check with meter set at x10 or higher.

http://www.soundtraxx.com/documents/manuals/lc_manual.pdf
 
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IronBeltKen

Lazy Daydreamer
Rex,

You've confirmed my worst fears. I have that same manual, I just didn't remember the exact page where I read about it not being designed for use with diodes.

Since I'm not an electronics wizard - I don't know how to tell which side of a diode is which - I've decided to scrap my LC decoder and forget about having sound :( . There is no other brand out there that sounds anything like a 1st generation EMD. QSI and Digitrax claim to, but they're aren't even close.

Working headlights are more important.
 
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stokesda

My other car is a 4-8-4
Ken,

Don't throw in the towel just yet! Check out the bottom part of this page from Litchfield Station's website on doing a sound install for an SD70MAC:

http://www.litchfieldstation.com/lobby/hods_kato_SD70MAC.htm

There is an issue with using LEDs on the LC decoders, but there is a "simple" workaround using an additional resistor and a small capacitor.

As for the diode direction, what Rex is basically saying is that the LED is a diode (Light Emitting Diode), and because of that, it acts kind of like a little electronic check valve. That is, it will only work if the electricity is flowing one way. There's a couple of ways to check which end is which:

1. You can use an ohm-meter as Rex described
2. Look inside the LED itself to see which lead has the little "flag" shape on top of it. The one with the "flag" will be the cathode (-). The other is the anode (+). Notice the orientation of the LED in the diagram of the website listed above.
3. One of the leads will be longer than the other. The longer one is the anode (+).
4. One side of the rim on the bottom of the LED lens will have a flat spot or a notch. This will be on the cathode (-) side.

The circuit diagram symbol for a diode is a triangle pointing against a flat line. Current flows in the direction the triangle is pointing, from the anode (+) to the cathode (-).

Also check out this website for a visual explanation of the above:
http://www.kpsec.freeuk.com/components/led.htm

FINALLY, there are other sound options out there. Soundtraxx just came out with several new DSD-101LC decoders, which may be a better option than the old 100LC "generic diesel" decoder. Have you considered ESU Loksound? Too bad there's (still) no Tsunami diesel decoder!
 

RexHea

RAIL BENDER
Ken, don't scrap it. Why not try a 1.5v incandescent bulb with a 560 ohm series resistor. May work better!

EDIT: Thanks Dan, good info. Ken, give both a try. Just don't give up yet. After re-reading, I believe Soundtraxx is saying the LED will glow after the function is turned off. I don't think they are saying it won't work at all. The link Dan gives may fix you right up.
 
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RexHea

RAIL BENDER
...Current flows in the direction the triangle is pointing, from the anode (+) to the cathode (-).
Uh Dan, I'm not trying to get something else going here and I only mention this because it is so easy to confuse, but unless you are talking about conventional current flow theory as used in engineering, the common electron flow theory is cathode (-) to anode (+), i.e. against the arrow.;) :)

EDIT: I noticed that you used a UK site and several countries still teach conventional, but as explained in the text, conventional current flow was found to be wrong; that because the electron was found to have a neg charge and was attracted to the larger protons in the nucleus of the atom, thus it moved. Because everything was setup for + to -, they kept on using it instead of electron flow theory. That is why U.S. engineering uses conventional; all the formulas were setup using the old theory and it is much easier to use than change. I personally like conventional current flow theory for ease in circuit analysis, but in actual field work, I found the electron theory much more easier in troubleshooting.

Of course I am old school, but you can always keep the diode parts straight in mind by remembering the old electron tube and the current flow being from the cathode to the plate. But, where's the filament!:D:D
 
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IronBeltKen

Lazy Daydreamer
Dan, thanks for an excellent link - it has the wire colors [blue/white/yellow] mapped to their corresponding output locations on the AT100LC board, which is exactly the one I'm using. Also, knowing which lead of the diode goes to which "color" will help prevent me from frying it the next time. The guy at the LHS who sold the LEDs to me, led me to believe polarity didn't really matter [yeah right].

My next question is: Can I keep using the Miniatronics LED in the set I already have - or should I order the parts from Litchfield Station? Then of course, there's the question of where do I find any 1/8watt resistors? Radio Shack doesn't carry anything smaller than 1/4 watt...

Rex, I'll give your idea a try if I don't get the diode thing figured out in a day or two. I'm going to get a readback of the CV that controls headlight dimming and see if that may be the cause of the weak lighting.

Thanx again guys!
 
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RexHea

RAIL BENDER
Ken, the wattage size is a recommended minimum value to ensure the resistor can handle the current/heat energy without burning out. You can use a larger wattage, but of course the resistor will usually be physically larger. 1/4 watt is fine. ;) :)
 

stokesda

My other car is a 4-8-4
Uh Dan, I'm not trying to get something else going here and I only mention this because it is so easy to confuse, but unless you are talking about conventional current flow theory as used in engineering, the common electron flow theory is cathode (-) to anode (+), i.e. against the arrow.;) :)

EDIT: I noticed that you used a UK site and several countries still teach conventional, but as explained in the text, conventional current flow was found to be wrong; that because the electron was found to have a neg charge and was attracted to the larger protons in the nucleus of the atom, thus it moved. Because everything was setup for + to -, they kept on using it instead of electron flow theory. That is why U.S. engineering uses conventional; all the formulas were setup using the old theory and it is much easier to use than change. I personally like conventional current flow theory for ease in circuit analysis, but in actual field work, I found the electron theory much more easier in troubleshooting.

Of course I am old school, but you can always keep the diode parts straight in mind by remembering the old electron tube and the current flow being from the cathode to the plate. But, where's the filament!:D:D
Rex,

OK, you busted me :D I'm by no means an expert on electricity. I didn't even stay at a Holiday Inn Express last night. I am a civil engineer by education, and electrical stuff has always baffled me. Now that you mention it, I do remember learning way back in high school (or maybe it was college?) that the current actually flows from (-) to (+). I also remember thinking this was counter-intuitive, based on everything I'd learned so far (thinking of batteries, etc.). Then it got really confusing when they started talking about magnetic poles ("Did you know the North Pole is actually a "south" magnetic pole, and vice-versa?" ... Huh? :confused: )

But all that aside, the point I was trying to make is that the (+) goes on the back side of the triangle thingy, and the (-) goes on the pointy side of the triangle thingy :D

I guess I should have worded it differently, given my lack of understanding of true current flow.

As for the UK website link I posted, it just happened to be the first one that came up on Google and had a pretty good diagram of the anatomy of an LED, so I just went with that one.
 
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RexHea

RAIL BENDER
Hey Dan, it was a good post, but I was afraid the polarities given might confuse. I know that when I first studied electronics ("electron flow theory") as an Air Force Technician it blew my mind about the diode's arrow pointing in the wrong direction to current flow and I could never find out why. Later and in my engineering studies, I then found out about "Conventional Current Flow" and how the diode symbol was drawn in accordance to its (backwards) theory. Heck, I even remember seeing old US Navy training films that showed positive to negative.

To add to the confusion, the names by definition are the same: current is electron flow. Guess they just needed a play-in-words to signify there was a change in the theory.

I better shut-up before I confuse my old brain more.:confused: :D :D

That is a very good and informative web site. There are several out there and those who need some basics would benefit from a visit to them. REX
 

IronBeltKen

Lazy Daydreamer
Hi guys, just an update: I got my headlight working passably [for the time being at least] by moving the bulb ~ 1/2" away from the lenses; They seem to capture more light rays that way. And the problem wasn't my dimmer function being accidentally left on, when I pressed the F7 key it really dim <LOL>

Dan that's a great link about LEDs, I printed it out along with the Litchfield decoder page - thanx again for sharing it!
 
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RexHea

RAIL BENDER
Ken, is that the 12v bulb you are talking about? Just curious, but I wonder what the voltage is coming out of the decoder. If it is less than 12v, that would explain the dim light. I know you can measure the volts.;) Just set your meter to volts and measure across the bulb.:) Another thought: What is the track voltage? That measurement requires a digital meter set on A.C. volts. There is another way to do it with an analog meter described in the Digitrax manual section of track voltage. I would post it, but I have forgotten:eek: :D .
 

IronBeltKen

Lazy Daydreamer
Rex,
I'll try that when I get home tonite. I've been a tad gun-shy about hooking a VOM to a decoder, I think that caused me to fry a few back in 2003 [when I first started dabbling in DCC]. I'm glad I don't have to disconnect any components/wires from the decoder...
 




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