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Red and green LED's circuit

Discussion in 'LEDs and Optoelectronics' started by adams, Oct 19, 2013.

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  1. adams


    Oct 19, 2013
    Hi All,
    Can you help me with this circuit?
    I want to design a circuit that includes 12V Bulb, red and green LED's. When the bulb is lit I want green LED only to light as well. When the bulb is blown (current not flowing throuh it) I want red LED to light only.
    Thank you for any suggestions.
    Last edited by a moderator: Oct 20, 2013
  2. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    Nov 28, 2011
    What is the power or current rating of the light bulb?

    Are you using a 12V DC supply?
  3. adams


    Oct 19, 2013
    DC. 12V battery or 2 if required.
    5W Bulb.

    I am working on the project for college. It is an assembly machine for bulb 501 to push fit to bulb holder. One of the station of that design will test the bulb if its working properly. I want to connect it to the plc through a relay and if its ok dump it to one box, if it is blown dump it to reject box.

    Would look nice if on top of that station I would have two LED's red and green to indicate wheter the bulb is OK or not.
    Last edited: Oct 20, 2013
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    OK, so you don't actually need the lamp to light.

    All you want to know is if it's blown or not.

    That's an easier problem.

    This would be my first solution:


    However, when I looked at this I realized that a far simpler solution is:


    Note that neither circuit can distinguish between a working and a shorted bulb.

    Attached Files:

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