I know there are a few threads about this and some interesting articles on the internet. I was wondering if there was anything new that let you use the original lighting (including the LED that change color). Perhaps using a Zimo 699KV ? Hoping to keep the lights available at all times on DCC,
Andrew
Andrew-
The challenge with the classification LEDs is that they are common cathode (i.e. common ground), and the Zimo decoder output provides a common V+. The white/black wires that feed the LEDs on the PCB in the front of the engine expect 12V or more, and the color switches with polarity. If white is + and black is -, the red LEDs go on, and if the polarity is reversed, the green LEDs go on.
You could potentially feed these from an H bridge with the polarity controlled by the headlight output, assuming you want the colors to track the headlight/reverse light.
Of course these red/green classification lights are fantasy, and should (in my opinion) just be replaced with white lights anyway. A green light means that a second unit of the same train is following. A red light would only be displayed on a rear-facing engine on the back of a train. It’s hard to imagine an F3 in that situation. You could easily clip off the red/green LEDs, hot glue some white ones in the shell, and feed them from one of the Zimo’s drivers with a CL2N3 in series.
What Eric said.
I have looked for white/green common anode leds to replace the nonsensical red/green ones, I thought I found them once… I would just replace with white, and depending on your railroad, leave them on all the time in forwards, or have them commandable.
Certain railroads ran every freight as an extra, since they were not part of a regular schedule.
Greg
Hmm… maybe I can have some made… at work, so those LEDs on USAT diesels are 5mm leds right?
Greg
Greg Elmassian said:
Hmm… maybe I can have some made… at work, so those LEDs on USAT diesels are 5mm leds right?
They are 3 mm.
I found some common cathode green and white in 3mm … still researching… I think I’d best just make a small circuit to invert the logic to allow common cathode, can’t find the common anode
I don’t ever expect to run two units of the same train, so I haven’t worried about it.
Eric Reuter said:
… A red light would only be displayed on a rear-facing engine on the back of a train. It’s hard to imagine an F3 in that situation.
I can see it in a push pull operation, with a F unit on both ends of the train. Or, as in the PATrain, a control car at one end, and an F unit on the other end.
Welcome AJ !
Eric Reuter said:
I don’t ever expect to run two units of the same train, so I haven’t worried about it.
Never say never…It’s like preparing for Y2K…wait that’s over so why not plan on preparing for Y 2.9 and 3/10’s K then?
I would go with negative type logic and for a common anode dual led I would ground the bias resistor on the high side to deactivate the led.
Just tie the cathode to common/ground.
The 7545X series of dual drivers would work well for doing this as they are dual opencollector IC chips and 300ma output. Also great for driving relays on the revolution function keys as a 2ma input will give you a great driving current.
So you would invert the sense, so function on is LED off?
But my Zimo handheld will be glaring at me with a bright yellow LED !!! (https://www.largescalecentral.com/externals/tinymce/plugins/emoticons/img/smiley-surprised.gif)
Yes, using transistors is another option, I looked at that, but I liked the complete isolation of the opto. The opto itself is only 50 cents. for my bicolor led, 2 optos and 3 resistors, simple circuit, solder the resistors to a 8 pin dip wirewrap socket and you are nice and compact.
Greg
Dumb question…
Why can’t you just wire the LED class lights to a lighting function output? Much like ditch lights? Then just control with you throttle? Assuming you replaced the red/green with white.
bicolor led… 2 leds with a common. Common cathode is all I can find. Simple answer is you need common anode on DCC decoders, “common” is positive, not negative.
bipolar would probably be easier, but those are even harder to find. White and Green is an unusual combination.
Greg
Thank you everyone.
It looks like I might do the simple down and dirty install for now 
and perhaps replace the classification lights with white LEDs
Andrew
That LED is a bicolor, bipolar led… i.e. just 2 leads, polarity gives different colors.
Different wiring than a bicolor common anode/cathod led (3 leads)
Check this page, and it has a schematic to control the bipolar, bicolor led with 2 function outputs.
(you can independently control the red and green colors)
Greg
7545X is only 29 cents at Jameco and has 2 separate open collectors (300ma total), 200ma each output). And for revos it could drive a smoke unit!!
Greg Elmassian said:
That LED is a bicolor, bipolar led… i.e. just 2 leads, polarity gives different colors.
Different wiring than a bicolor common anode/cathod led (3 leads)
Check this page, and it has a schematic to control the bipolar, bicolor led with 2 function outputs.
(you can independently control the red and green colors)
Greg
Greg
What Page?
Tom
Whoops!
about 2/3’s of the way down the page… the stock led in the USAT locos is a bipolar bicolor…
Greg
