Bob’s LED lighting tip

Got this in from Bob:

“Hy Al, I have found a neat little circuit to lite LEDs. I use a dual LED with both Red and Grn and common anode (+).

What I needed was a way to switch from red to grn without having to have a relay as I only had a single switch SPST available. I connect the anode to a 2k resistor to +12 Vdc, and one ot the LEDs to Grd. Then I connect a 1.5K resistor to the other LED to a switch to -12 Vdc. When the switch is thrown the negative LED lights and the positive LED is backward biased. When the switch is open the positive LED lights. The resistors may be decreased for more light output.

My switch is an over the center crank that hits a pin to make the connection. This is very low cost switch machine for a lot of switches.

The Best


And Bob’s tip got me thinking – there’s been a number of posts on them over the years.

Matthews lighting ‘how to’ is excellent.

And so is Dave’s.

Mark sheds light on a few tips too.

And if you want to light up your coaches, have a look here.

In fact, the list is endless. There’s years and years of posts now…

Hope you’ve found them helpful!

That’s all this time folks, it’s all becoming a little thin on the ground so please do mail me if you have anything you’d like to share.

If you want to search through the archives by the way, you can if you’re a Beginner’s Guide member.



PS Latest ebay cheat sheet is here. Some cracking deals about at the mo.

13 Responses to Bob’s LED lighting tip

  1. Ben Hawkins says:

    Very good Pictures, What about seeing some O gauge Layouts also, Plus the Buildings, Roads & Scenery

  2. mark st john says:

    excellent advice
    keep em runnin fellas
    stjohn in long beach calif

  3. Mike Street says:

    Am I being thick, what’s the difference between ground and -12vdc?

  4. Thomas Murphy says:

    Good thinking, Bob.

  5. Wayne McClelland says:

    Hi Al
    It’s been a while since I last called but this note prompted a me to call.
    I changed all my Locomotives (with ) lights removing the incandescent
    lamps replacing them with LEDs. The advantage of doing this is that I
    don’t have the Voltage drop created by the incandescent types (sucking
    3 – 4 volts) giving me more usable power on the track

    Kind regards to all
    The colonial from Down-under

  6. Chandrasekar R says:

    Thanks Bob,

    Useful tips. I am intend to create a small railroad. I am looking for the tips relating to LED’s.

    looking for more tips.

    Thanks Alastair Lee.


  7. Cary B says:

    Al, Once again thanks for sharing many modelers tips on led lighting.

    Cary B

  8. tom says:

    Just i`m dumb the wiring needs a better explanation Bob sorry, sounds interwsring. Tom AZ

  9. Mike Walne says:

    There’s a simpler, cheaper method. Uses only one resistor and supply rail.
    Connect the common anode via a resistor to the +12V rail.
    Connect the GREEN LED to GND..
    Connect the RED LED to GND via the switch.
    With switch open green light, with switch closed red light.
    Works because the red LED forward voltage is lower than the green.


  10. Craig Burton says:

    Excellent tip! Keep them coming,Thank You Al

  11. I am using these Bi-Color LEDs in my control panel for my turnouts. I use a DC transformer for the lights and to operate my switch machines. My layout is a 3-rail O gauge AC system. I wanted power indicator lights in my Control panel, so I added a rectifier to those LEDs.

  12. Norton A Willliams says:

    @ Mike Street

    He is using a bipolar power supply that provides +12 and -12 VDC. These voltages are in reference to Ground. The + 12 is 12V above Ground and the -12 is 12 V below Ground.

    Dos that help?

  13. Erick says:

    Would like to see more.

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