On my old Rivarossi Allegheny, I'm planning to wire in a "firebox flicker" to the extra function wire on the Digitrax DN 136 decoder that is already installed. This old loco has an incandescent bulb for the headlamp and reverse light, but I want to use an LED for the firebox. I've got some 680(?) Ohm resistors to use with the LED. I think Digitrax recommends 680ohm resistors? Anyway, does it work ok to mix LEDs and bulbs on the same decoder, splicing into the same blue common wire? It has the extra wire for the third FX function, but I'm assuming uses the same common blue wire to the (8 pin) plug? Will it affect the headlight in any way? It's already pretty dim.... thanks in advance for any advice!
Mike C.
I don't think that mixing LEDs and incandescent bulbs will cause any problems as long as you don't exceed the maximum draw for the decoder function. That is not going to happen in your case. The decoder doesn't know what it's hooked up to.
A couple of comments:
Using a 680 ohm resistor will be fine but it will make the LED very bright. I would see how it looks before reassembling the locomotive. It might be much brighter than the typical firebox 'glow'. On the other hand, you may think it looks great. If you do want to dim it a bit, try resistors in the 4000 - 10000 ohm range.
This is perhaps too obvious a question, but why not convert everything to LEDs? Your dim headlight and reverse light can be made to look much more realistic. Note that if you do decide to convert to all LEDs you will want to experiment with higher value resistors for the headlight and reverse light too. Otherwise they can be too bright to represent a steam era light. Also, make sure you use warm white LEDs or they will look horrible.
Dave
I'm just a dude with a bad back having a lot of fun with model trains, and finally building a layout!
wobblinwheel It has the extra wire for the third FX function, but I'm assuming uses the same common blue wire to the (8 pin) plug?
isn't the blue just a common ground? shouldn't matter whether you're driving an LED or lamp
greg - Philadelphia & Reading / Reading
gregcisn't the blue just a common ground? shouldn't matter whether you're driving an LED or lamp
Indeed the blue is common for all the non-motor functions. But do note that the blue wire is most often referred to as "function common (+)", meaning it is the DC positive side, which must be connected to the correct side of the LEDs for them to work. I've got to the point that I know (or have notes) for which side of my LEDs to hook up the blue wire, knowing what works for each type LED I have.
Paul
Modeling HO with a transition era UP bent
Blue is common, but it's common +. The function drivers connected to tha various wire colors are open-collector circuits, which is a fancy way of saying "switch to ground"
There is no problme having some functions being light bulbs and some having LEDs - the only thing to watch out for are decoders that come with current limited outputs, often this means there are more than one blue wire connection, one which is limited for LEDs and one which is full power. Connections to the limited common tend to not need resistors, LEDs on the full power output need resistors. The usual starting place is 1K. That usually makes an LED PLENTY bright - in fact for some of the smalle surface mount types, it might still be too bright, so a larger value may be required.
Finally, the OP mentioned a Digitrax decoder - Digitrax decoders tend to not do the 'effects' - flashers, blinkers, flickers - as well with LEDs as they do with incandescent bulbs. Other brands seem better at using LEDs. With Digitrax and a few others, there is a CV to set to different values if you are using incadescent or LED. As long as all the effect lights are the same time - it won;t matter. IE, you set the CV for LED to use an LED firebox flicker but the headlight is an incadescent bulb. But if you have an incandescent Mars light and want to add an LED strobe on the roof - one or the other won't work as well depending on the setting for lamp or LED. It's because incandescent lamps gradually dim out when the power is removed, LEDs more or less shut off instantly. To keep an LED from just looking like it's mostly off, to get a special effect the LED has to be ramped up and down, whereas the same ramp applied to an incandescent bulb would make it appear mostly on all the time.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
i think you're right (thanks for the correction) but i would think the manual for the decoder would spell it out (i didn't see it mentioned for the TCS T1 that I use)
it would make more sense for the common to positive and the control lead to pull to ground.
Kind of easy. lol
http://www.members.optusnet.com.au/nswmn1/Lights_in_DCC.htm
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.
I bought about 200 680ohm resistors from Amazon, as well as 200 warm white LEDs that look very much like bulbs. I now often wire two or three resistors in series to dim the led. As far as the head lamp, it's the TINIEST bulb I've ever seen! I have yet to figure how to work an LED. I do think it would be a neat effect to have a rather bright flicker coming from the cab!
I do remember some years ago seeing fire box flicker video from an oil fired loco. Always flickering, brightly. Now that is quite a fire box flicker compared to a coal fired loco. Coal fire usually only flickers when air jets on but sure that varies.
The "flicker" from the Digitrax decoder using an LED is somewhat subtle, but for a coal burner, I think it will look ok. I think the slight illumination of the well-detailed cab should be GROOVY! (when was the last time you heard that one?)
wobblinwheelAs far as the head lamp, it's the TINIEST bulb I've ever seen!
You say they look like bulbs but they are tiny. Did you buy surface mount LED's? Regular led's are 3 mm about the same size as bulbs, Surface mount's are tiny, barely bigger than FDR's eye. Good for ditch lights. Here are some courtesy Streamlined Backshop
Henry
COB Potomac & Northern
Shenandoah Valley
I'll have to study how the bulb goes into the housing. I'm pretty sure the new models use LEDs, so I should investigate how they're doing it.
Mike C,
You should find this chart helpful/useful. The LED You're speaking of, coud be a 1.8 mm. Chart courtesy of Lights4models.
The gooseneck light outside the small door, in this photo, is a Pico Chip, one of the smallest Led's made.
Take Care!
Frank
Wow, I didn't know they made em that small!
wobblinwheelWow, I didn't know they made em that small!
You can get them pre-wired which I strongly recommend. I have soldered leads to a fair number of small SMD LEDs but I quit when the LEDs were offered with leads already attached.
https://www.ebay.ca/itm/0402-0603-0805-1206-SMD-Pre-soldered-Micro-LED-White-Red-Blue-Diodes-20cm-Line/382349082395?hash=item5905c7ff1b:m:mnr2pV915z77DafnTrnRONA
I use 90 second epoxy to glue them into place. It's a bit of a PITA because the "90 second" epoxy seems to take much longer than 90 seconds to set up hard. During the curing time you have to be very careful to keep the LED in its exact place or it will move even after the epoxy starts to firm up. You will be very unhappy if the LED is positioned incorrectly.
Don't forget the resistors!!!
Do handle the LEDs very gently or you will break the leads off.
hon30critter I use 90 second epoxy to glue them into place. It's a bit of a PITA because the "90 second" epoxy seems to take much longer than 90 seconds to set up hard. During the curing time you have to be very careful to keep the LED in its exact place or it will move even after the epoxy starts to firm up. You will be very unhappy if the LED is positioned incorrectly.
I use Elmer's Clear Glue, available from any craft store like Michael's, you can even use it to make "bulbs." The dried product is flexible, paintable (to eliminate light leakage) and easier to work with than epoxy.
Thanks EVERYONE for all your suggestions! You have given me some great ideas!
Also Thank You Mike for taking the time to acknowledge the fact that others have taking their time to try and help You out. Too bad a lot of others don't follow Your common courtesy.......
Good Luck, on Your project!
Metro Red LineI use Elmer's Clear Glue, available from any craft store like Michael's, you can even use it to make "bulbs." The dried product is flexible, paintable (to eliminate light leakage) and easier to work with than epoxy.
Hi Metro Red Line:
How long does the Elmers Clear Glue take to cure to the point where the LED won't move anymore? Also, how do you hold your LEDs in place while the glue cures? I have had occasional problems where the LED shifted before the epoxy set up, even with the 90 second stuff. I find holding things in position for several minutes to be very tedious.