A Doouble pole Double throw switch would do the honors.
I'll make a sketch in a few minutes but, in short, one leg would feed the roundhouse track and the other leg the LED. When roundhouse track is off, the opposite contact would turn on the LED.
LED by Edmund, on Flickr
With the same switch you could have a red and green (or yellow, more appropriate) to show the track is active.
Regards, Ed
The easiest way to accomplish what you want to do without interacting with the track power would be to use a double pole switch, where one pole controls the track power and the other controls the LED power.
-Kevin
Living the dream.
LastspikemikeWouldn't a SPDT work more easily?
The OP does not mention if his track is powered using DC or DCC supply.
If DC, the voltage to the track would be quite low if moving light engines in/out of a roundhouse or service track. Speed (voltage) down or stopped = no current for LED.
If DCC it would work, the LED across the rails with a resistor but why add extraneous circuitry to the track wiring? Sometimes diagnosing track problems is tough enough without having a bunch of extra LEDs to contend with.
A DPDT doesn't cost that much, if at all, more than a SPDT. Keep the indicator lights on a separate supply. Easier to wire? Not so much more complicated to make a difference.
By the way, I am using DCC. And I did try wiring the LED with a resister to just one side of a DPDT toggle switch, in essence making it a SPDT, but when I do this the LED light only comes on when the power is switched off and there is a locomotive on the isolated track. As soon as I remove the locomotive the light goes out.
Yes you do, otherwise when you drive your engine off the turntable that track could be dead and the engine will just stop.
That is about as prototypical s you can get to put one in the pit.
Lastspikemike Wouldn't a SPDT work more easily? Power delivered to the track in one position and to the red light in the other. One power wire.
Wouldn't a SPDT work more easily? Power delivered to the track in one position and to the red light in the other. One power wire.
My rule is to only use that precious DCC power for trains. In earlier years, people found it convenient to use DCC power for signals, streetlights and even structure lighting. This would reduce available power for the trains.
Yes, a LED only uses a tiny bit of current, but I try to be pretty strict about adhering to this personal rule and generally good practice.
It takes an iron man to play with a toy iron horse.
I agree that the DCC power bus should only be used for DCC. That is why I have two DC busses, one for the Tortoise motors and the other I labelled Accessories and use it for lights and Rapido uncouplers and eventually for signals.
OK, I followed gmpullman's diagram and it works great, thanks! I would though like to know how to do this with a bi-color LED so I only have to drill one hole in my control panels to indicate the status of a track's power. My control panels are already pretty crowded with two lights for each turnout.
JPDI would though like to know how to do this with a bi-color LED
Easy enough to do with a three-leg LED. The two leg variety requires a reversal of the anode/cathode whereas the three leg is slightly different.
LED_rev1 by Edmund, on Flickr
In the modified sketch, essentially the three leg is just like two common LEDs sandwiched together sharing the same (usually) cathode. Note that now the + is the side switched since most 3 leg LEDs have a shared cathode or minus side.
ndbprrThat is about as prototypical s you can get to put one in the pit.
Oh, that never happens, does it?
3734GTW_Pontiac_6-9-55 by Edmund, on Flickr
Ed, any chance you could draw a diagram using a 2-leg red/green bi-color LED?
Rich
Alton Junction
richhotrainEd, any chance you could draw a diagram using a 2-leg red/green bi-color LED?
I think this should work.
LED_rev2 by Edmund, on Flickr
wrench567Going through the back wall of the roundhouse happened too.
Do tell —
Runthrough by Edmund, on Flickr
The occasional errant diesel has been observed, too
LAUPT_19-L by Edmund, on Flickr
Cheers, Ed
gmpullmanThe occasional errant diesel has been observed, too. LAUPT_19-L by Edmund, on Flickr Cheers, Ed
I just learned something from that picture.
I always thought that if the locomotive body was lifted up, the trucks would stay on the rails. I guess that is not true. There is something holding the Blombergs to the frame, quite obviously.
SeeYou190I always thought that if the locomotive body was lifted up, the trucks would stay on the rails.
Passenger cars are like that, too. Most will have a plate saying "Locking center pin, remove from inside car".
The idea of the safety chains was the same, too, keep the trucks aligned with the car as much as possible. With Diesels I'm sure there was consideration for the traction motor cabling, too. I don't know if the ground fault would trip quick enough to prevent arcing with the possible presence of leaking fuel?
Thanks again GMPULLMAN, I will give this bi-color diagram a try.
JPD,
Make sure you double-check what type 3-legged bi-color LED you have/purchase. Most are common cathode (-) type but some do come with a common anode (+). That will make a difference how the LED is wired.
I needed a red-white LED to correct the classification/marker light colors on an Atlas H16-44. The locomotive came with red-green markers and the NYC used red-white. The only version available at the time were red-white LEDs with a common anode.
Even though I would imagine that most red-green LEDs are common cathode type, I wanted to throw that bit of info out there.
Tom
https://tstage9.wixsite.com/nyc-modeling
Time...It marches on...without ever turning around to see if anyone is even keeping in step.
I blame myself for this because of my inability to make sense of these three hand drawn diagrams. But, I am confused on the various wire connections although I have wired plenty of DPDT switches over the years.
OK, I tried following this diagram, but either it does not work, or I have done something wrong.
The problem appears to be with the jumper between the positive and negative DC inputs. When I do this, nothing happens. When I remove the jumper and then the LED lights green until I flick the switch and it goes off. If I disconnect the wire without the resister leading from the LED and touch it to the negative, then it lights green, if I flick the switch and touch the wire to the positive it lights red.
The video by Tom's Trains and Things shows a diagram using three resistors, see https://www.youtube.com/watch?v=YrVDv65vzPI. However, I have a hard time figuring out how to apply his diagram.
Any suggestions?
gmpullman richhotrain Ed, any chance you could draw a diagram using a 2-leg red/green bi-color LED? I think this should work. LED_rev2 by Edmund, on Flickr Regards, Ed
richhotrain Ed, any chance you could draw a diagram using a 2-leg red/green bi-color LED?
JPDdoes the resister go on the Anode or Cathode leg or does it matter?
It doesn't matter which lead you solder the resistor to; it only matters that you do it. Otherwise, the LED becomes a momentary LED and goes *poof*.
For simplicity and uniformity...with a 3-legged LED...I would solder the LED to the center lead. But that's me...
tstageFor simplicity and uniformity...with a 3-legged LED...I would solder the LED to the center lead. But that's me...
This is the most direct solution. Otherwise a resistor will be needed on each anode lead.
Joe
JoeinPA tstage For simplicity and uniformity...with a 3-legged LED...I would solder the LED to the center lead. But that's me... This is the most direct solution. Otherwise a resistor will be needed on each anode lead. Joe
tstage For simplicity and uniformity...with a 3-legged LED...I would solder the LED to the center lead. But that's me...
I recall threads from years past when the late Randy Rinker would comment about resistors and his advice was to avoid taking the shortcut of simply using one resistor on the anode, or whichever side is common.
I have taken that stance and found that there are times when I want a slightly different value, especially when wiring color light signals where EACH of the red, green and yellow LEDs have a different light output.
Likewise on some panel lights I've wired I've found the red color to be extremely bright while a green or yellow would be hard to recognize if it was lit or not in a bright room.
I've got buckets full of resistors on hand and I don't think I've paid more than 2¢ each for them. But, sure, you could get away with one on the common if you'd like.
Your choice.
tstageMake sure you double-check what type 3-legged bi-color LED you have/purchase. Most are common cathode (-) type but some do come with a common anode (+). That will make a difference how the LED is wired.
gmpullmanIn the modified sketch, essentially the three leg is just like two common LEDs sandwiched together sharing the same (usually) cathode. Note that now the + is the side switched since most 3 leg LEDs have a shared cathode or minus side.
I mentioned that 3 leg (usually) are common cathode. The eBay link I provided are for that type so the OP can use that as an example and presumably find the same type.
Thanks for reiterating the caution.
gmpullman Easy enough to do with a three-leg LED. The two leg variety requires a reversal of the anode/cathode whereas the three leg is slightly different.
gmpullmanI recall threads from years past when the late Randy Rinker would comment about resistors and his advice was to avoid taking the shortcut of simply using one resistor on the anode, or whichever side is common. I have taken that stance and found that there are times when I want a slightly different value, especially when wiring color light signals where EACH of the red, green and yellow LEDs have a different light output. Likewise on some panel lights I've wired I've found the red color to be extremely bright while a green or yellow would be hard to recognize if it was lit or not in a bright room.
Very good point, Ed. Indeed color LEDs all have different illumination voltages (generally between 2.2 & 3.0V) and would need different resistor values to make their output equivalent with one another.
JPDMy control panels are already pretty crowded with two lights for each turnout.
My "control panels" are usually a switch or two on the fascia at each town on the layout, and there are no lights involved. However, at the two locations where there's a turntable, I use an ON/OFF switch for track power, and a rotary switch to select the track which I wish to energise...
...you could save room by using a similar set-up with a single switch for power, and a rotary switch, with suitable LEDs at each position.
Wayne