Drive Two LEDs with one switch

Discussion in 'The Projects Forum' started by seabear, Aug 2, 2012.

  1. seabear

    Thread Starter Active Member

    Feb 20, 2009
    34
    0
    Hi again, I would like to have a red/green indication of the position of a switch. I could use 2 separate LEDs or if feasible one of those dual color LEDs. (refer to attached diagram) In either case I would really appreciate if someone could draw out a basic circuit that I can use.

    1. how to reduce the 12v dc to something the LEDs can handle
    2. how to connect the LEDs so that one of them is always on depending on the position of the switch.

    thanks very much
     
  2. wayneh

    Expert

    Sep 9, 2010
    12,136
    3,054
    Here's one idea. Both LEDs would be on when the switch is closed.
    [​IMG]
     
  3. seabear

    Thread Starter Active Member

    Feb 20, 2009
    34
    0
    Actually that would make one or both on at the same time and what I really want is to only have one on at one time.
     
  4. wayneh

    Expert

    Sep 9, 2010
    12,136
    3,054
    This is the best I can think of at the moment. I'll bet there's a better way, but I can't see it.
    [​IMG]

    [update] Oops, this won't work if the unseen circuit impedance is not >1K. If it's not, the left-most LED will blow just like a fuse. The diode-drop approach below is more versatile.
     
    Last edited: Aug 7, 2012
    seabear likes this.
  5. KJ6EAD

    Senior Member

    Apr 30, 2011
    1,425
    363
    Just a few points of information that may or may not be useful:

    1. You can get illuminated switches to do essentially that with no additional hardware.
    2. Using a SPDT switch would simplify the design.
    3. LEDs made with a built-in resistor for 12V are available.
    4. Single color LEDs generally look better than dual color LEDs, especially in brighter ambient light conditions.
     
  6. seabear

    Thread Starter Active Member

    Feb 20, 2009
    34
    0
    thanks all for the replies, I might just take the simple approach and use stdt switches... good advice on the bi-color leds too.
     
  7. daviddeakin

    Active Member

    Aug 6, 2009
    207
    27
    Here is another method. When the switch is closed, only the green LED lights because the forward voltage of the green LED is less than the forward voltage of the red LED + diodes. When the switch is open only the red LED can light.

    [​IMG]
     
    Last edited: Aug 7, 2012
    seabear and absf like this.
  8. seabear

    Thread Starter Active Member

    Feb 20, 2009
    34
    0
    that looks pretty good, I think I will try that, thanks
     
  9. daviddeakin

    Active Member

    Aug 6, 2009
    207
    27
    Incidentally, that circuit came out of a book on power supplies where the switch was replaced with a fuse. As long as the fuse was OK the green LED lights and acts as a 'power on' indicator. If the fuse blows the red LED comes on to inform you of the problem!:)
     
Loading...