Hi folks,
We have been working on the control panels for the club's new layout and we have encountered a problem. We wanted to use two bi-colour two lead LEDs for each toggle switch, one in each of the through and diverging routes. We set up a test circuit and tried it with one LED in series with the motor and it worked fine. Then we added in a second LED in parallel to the first but with the polarity reversed. When we did that all we got was the red indication on one or the other of the LEDs but no green.
How do we solve the problem?
EDIT: The following questions were pretty dumb in hindsight:
Is the red side of the bi-colour LED drawing all the power? Irrelevent. See Kevin's post below.
If I understand the LEDs, we can't put two of them in series with the polarities opposite because one or the other of them will block the power. Is that correct? No, that is not correct!!
Do we have to use three lead bi-colour LEDs with a resistor on the red side to equal the draw? If so, do we want common anode or common cathode? NO.
Can you tell I'm guessing here and I don't know what I'm talking about?? I'll stop guessing.
By the way, the simplest solution would be to just use one LED on the through route, but we are dealing with club members some of whom might not be able to figure that out especially when they are approaching the diverging route from that end of the turnout.
Thanks,
Dave
I'm just a dude with a bad back having a lot of fun with model trains, and finally building a layout!
Dave,
.
My experience with bi-color LEDs, which might ber outdated, was that they would light one color in one polarity and the other color if current was reversed.
You would need to use both SPDT auxiliary contacts on the Tortoise to do this, wired in a fashion similar to the DPDT reversing switch on a DC power pack.
If you wire two bi-color LEDS in series they will both light in a color depending on the polarity of the input voltage.
I have never seen a three lead bi-color LED.
Maybe some of this will be helpful.
-Kevin
Living the dream.
SeeYou190If you wire two bi-color LEDS in series they will both light in a color depending on the polarity of the input voltage.
Ah ha! That is the answer. I just did a test and bingo! Both colours lit up just fine.
Thanks Kevin!
P.S. I feel a bit stupid. I thought I knew something about LEDs but I have never dealt with a bi-colour LED before.
Yeah they have to be in series, in parallel, one of them is seeing the voltage drop across the other one and that's it. The red and green LEDs have slightly different characteristics and that's why only the red one lit when in parallel.
And 3 lead bicolor LEDs are actually quite common. They can be had with either common anode or common cathode, and I've even seen ones where the outer two leads are two LEDs in series and the middle leg was the junction between them. 3 lead bicolor LEDs require the contacts on the Tortoise, you can't easily stick them in series with the motor wires like a 2 lead type.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
SeeYou190I have never seen a three lead bi-color LED. .
Having only seen them on Ebay and never used one, I thought they were all 3 lead
Henry
COB Potomac & Northern
Shenandoah Valley
BigDaddyHaving only seen them on Ebay and never used one, I thought they were all 3 lead
Yes, it appears my experiments with bi-color LEDs is about 20 years or so outdated.
I am obsolete.