Tortoise & Bicolor LED Wiring

Discussion in 'FAQs' started by kchronister, Jan 9, 2006.

  1. kchronister

    kchronister Member

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    I'd like to wire my tortoises (thrown with panel toggle switch) to two bicolor LED's, one for each track. So that when the switch is thrown, the 'open' track is green and the 'closed' track red...

    Now, I THINK the easiest way to do this is to wire up to bicolor LED's per the standard wiring to a toggle (see image below). This, to my limited electronics ability, seems that they would be set in opposite... Voltage always going to the + of one (green) and the - of the other (red), giving the desired behavior.

    Is that right? If not, how would I go about it?

    Thanks,

    Kris

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  2. Russ Bellinis

    Russ Bellinis Active Member

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    I'm no electronics expert, but I think they make bicolor leds that change from red to green when the polarity is reversed on the same led.
  3. kchronister

    kchronister Member

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    Yes, exactly! Those are what I'm looking at.

    So my "I'm even more of a not-expert than you" question is does simply installing them the same way as single-color LED's result in the color flipping when you change the toggle?
  4. Russ Bellinis

    Russ Bellinis Active Member

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    That is my understanding, Don (e-z-days) or others with more of an electronic background would know better than me. You might try wireing up one led and see what happens. It won't hurt them to wire backwards, the worst case scenario is that when you reverse the polarity, it won't light at all.
  5. kchronister

    kchronister Member

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    Thanks Russ. That's probably exactly what I'll do, tho it'll be a bit before I can do so. If we don't get a more expert input here, I'll advise the group on outcome.

    Kris
  6. ezdays

    ezdays Out AZ way

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    There are several types of bi-color LEDs dependent on the application. It's been a long time since I had any need for them, and things change quickly in the electronic world. But, here are two wire type where if you change the polarity of the voltage, the color changes. There's another with either a common cathode or common anode where you light each color separately. This one you can actually get a third color. Light one you get red, the other you get green and light them both and you get sort of a icky yellow color. I've also had some that were four-wire with separate cathode and anodes.

    That being said, you can use the first type to do the job without going through a switch. Just be sure you use a current limiting series resistor. For most you can use around a 2.2K and get 10 mA which is enough to light them. Some may require 20 mA for them to light bright enough.

    Be sure to use a resistor on any LED, (even single color) that doesn't have one internally though, since you will burn it out even if it's wired backwards.
  7. Russ Bellinis

    Russ Bellinis Active Member

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    Thanks for the corrections, Don. I knew I was forgetting some things in my answer to him.
  8. ezdays

    ezdays Out AZ way

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    Not that much. The series resistor is important in either direction. Too much resistance won't hurt the LED but too little will.:)
  9. jim currie

    jim currie Active Member

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    you can still get the two lead bicolor led's in frosted or water clear.Kris in you are interested in some PM me.
  10. caellis

    caellis Member

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    If you use Bi-Polar LED's you only need one in either leg of the tortise
    That means place a Bi-Polar LED in only one lead and forget the resistor.
    The Tortise only draws 15 Milliamps stalled. The Tortise acts as a current limiting resistor in this case.

    As you reverse the voltage to the Tortise the LED will be RED or GREEN depending on the polarity. You only need to reverse the wires if the LED lights with the opposite color you want.

    This is the simplist circuit you can use!
  11. jim currie

    jim currie Active Member

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    never having seen a tortise but in reading it has accessory contacts which i would use as led's are very susceptible to voltage spike's and surges.
  12. ezdays

    ezdays Out AZ way

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    Welcome to the Gauge. We seem to live on opposit ends of the valley, but welcome neighbor.

    What you are suggesting is that the LED be placed in series with the tortise. Like Jim, I'm not familiar with the tortise circuitry, but I can see two potential problems here. One, you are taking away about two volts of the tortise operating voltage by putting a load (LED) in series with the supply voltage. And secondly, I'm assuming that the tortise is motor or solinoid driven, and if so is inductive and will and Jim points out, generate spikes, some going negitive when the field colapses. I still think the best bet is a series resistor with the LED and resistor across the tortise voltage source.

    I could be wrong, never having done this, but those are two things I'd look out for before doing this.
  13. straight-track

    straight-track Member

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    Kris, Your original drawing is exactly how I have about 20 Tortoise machines wired with LEDs in my control panels on my layout. Had I had any bi-color LEDs at the time I would have used them in place of the red & green ones. I mount a double throw toggle switch with a red on one side and the green on the other. As Caellis says the tortoise machines provide enough resistance so that all works well. When you throw the turnout the LED color changes first to a dim color then brightens to full and vice-a-verses. I'll get a pix posted. Joe ! [​IMG]

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  14. kchronister

    kchronister Member

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    Sweet-looking control panel, straight track.

    For the general good, I'll mention that putting the LEDs in line with the tortoise is, in fact, endorsed by the Circuitron folks, and I've done that in the past without a problem. I just didn't know if the bicolors would work properly.
  15. ezdays

    ezdays Out AZ way

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    Glad to know that Circuitron sees no problems with series LEDs, and that the voltage drop would not be noticable. My comments were that I had not experience with tortise switches, but those were things that could be potential problems. Since they do say it's OK, then a bicolor LED would work since they are nothing more than two reversed LEDs in one lens package. The current flows in one direction and the red lights, it goes in the other direction and the green one lights.
  16. kchronister

    kchronister Member

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    Heck, a "heads up" never hurt anyone! Thanks.

    What they do say (and I think it's noted here too) is that while the motor is throwing the turnout, the LED will dim, then when it reaches the end of the throw and stalls, it will come to full brightness.
  17. pgandw

    pgandw Active Member

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    Don

    I have not tried one, but is my understanding that the Tortoise motor never turns off - it is allowed to stall when it reaches full throw. The stall current is very low - 16ma or less - so it does not overheat, and limits the current for LEDs. The only time when voltage spikes would be a potential problem would be when the motor is reversed to throw the opposite direction. But given the magnitude of the motor current, I don't think the spikes would be significant. Also, Circuitron requires no more than 12V DC power supply (and will usually operate fine at 8V) so a diode voltage drop is not a problem in most cases. This information is derived from the Tortoise manual and Tony's Trains.

    yours in wiring
  18. ezdays

    ezdays Out AZ way

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    That's good, one never gets too old to learn something. Fortunately, there's plenty around here to learn from and plenty of room in my brain for new stuff.tooth tooth I'm not sure if the room is from not learning much, or forgetting half of what I did learn.:D :rolleyes: :rolleyes: :D

    And yeah, when the motor reverses, it should throw a spike on the line, probably what we call "back" or "reverse EMF". Believe it or not, the reverse-biased LED will absorbe that spike as long as it is not too big or there too long. This is the reason one should always put a reverse-biased diode across the coil of a DC relay.:)
  19. caellis

    caellis Member

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    No problem with Bi-Polar in series in the Tortise circuit. I have about 30 such circuits on my layout using Bi-Polar LEDs. It doesn't really matter which lead you place the the Bi-Polar LED except reversing the LED will reverse the color that you get.

    You may also use regular LED's wired back-to-back with the same results .The Tortise machines work reliably as low as 9 VDC in my experience.

    In fact you must use two LED's back-to-back in this case as there must be a complete circuit which ever way you connect the DC. In other words with only one LED in the lead you would have the same circuit as if you placed a Diode in the lead. Afterall the 'D' in LED stands for Diode!
  20. straight-track

    straight-track Member

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    Don, Any negativity was certainly not intended. Having experience with the tortoise/LED hook up, I just wanted to help . Joe :)