how to make red LED switch to green and back?

Discussion in 'The Projects Forum' started by damian, Apr 22, 2010.

  1. damian

    Thread Starter New Member

    Nov 2, 2009
    Hi guys,

    I have to build a fake security card box that is mounted on a wall for a show I'm working on. The action is this: a guy swipes his security card, the red LED goes green for a second, then switches back to red (thus showing that his card no longer works).

    Any suggestions how to make this action happen? The security card will likely pass through a slot in the box, so there might be a place to hide a switch.

    Thanks! Damian
  2. Wendy


    Mar 24, 2008
  3. retched

    AAC Fanatic!

    Dec 5, 2009
    You could replace the card reader head with a simple microswitch. When the card hits the switch, the red led lights.

    If you want it to go red for a second then back to green, you will need a little Bill_marsden.

  4. damian

    Thread Starter New Member

    Nov 2, 2009
    Hi guys,

    thank you for the response!!! This is likely exactly what I am looking for but I don't really know how to read the diagram (I am just starting to play with LEDs now, not having a background in electronics).

    If possible, is there a way you could dumb down that diagram so that I would know what parts to ask for at my local electronics store? I will bring your diagram with me and hopefully someone there can help me get everything together.

    OK, thanks so much gents!

  5. Wendy


    Mar 24, 2008
    Actually, schematics are as basic as it can get. They are what any shop would use to define parts. They are the language of electronics, a schematic is worth 10,000 words.

    I would highly recommend a 300 in 1 projects kit if you are serious about this hobby, that or lots of reading. The AAC text book shown above is another good source of education.

    Here is a modified schematic that might get you where you want to go.


    The two LEDs in this schematic are actually one part, a red green LED. The leads are connected together inside the package. The resistors need to be recalculated to match your power supply.

    Speaking of which, what is your power supply? This is critical.
  6. KL7AJ

    Senior Member

    Nov 4, 2008
    Oh, that Bill is a clever lad! (I know, because that's exactly how I would do it. :D )

  7. VoodooMojo

    Active Member

    Nov 28, 2009
    Here is one of Bill's circuits in pictoral view.
    It has a green and a red led.

    Also Bill's drawing with a simple green led delay off circuit added.
    Almost any small signal NPN transistor can be used.

    when the switch is activated, the green led will light and the red led will go dark.
    when the switch is released, the red led will light and the green led will remain lit for approximately 2 seconds at which time it will fade off rapidly.

    Add a switch at the Vcc to conserve 9 volt battery life when not in use.

    Any part of this drawing that is in error, please comment.
    Last edited: Apr 23, 2010