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2 transistors as SPDT?

Discussion in 'General Electronics Discussion' started by bigjayman, Feb 8, 2013.

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  1. bigjayman

    bigjayman

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    Feb 3, 2013
    I am trying to make a simple circuit where one LED is lit until a momentary button is pushed that will turn it off and turn on a different LED. The key component is the tactile switch I'm using, it is the perfect dimensions for my purposes but it is a SPST-NO. I'd rather not use a relay or an IC since I am trying to make this project as small as possible. I'm hoping I can use 2 transistors but I'm not having much luck figuring out how to make it work. Any help?
     
  2. Harald Kapp

    Harald Kapp Moderator Moderator

    11,513
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    Nov 17, 2011
    What exactly do you mean? is the momentary push buttton meant to toggle between the two LEDs, or do you want LED 1 to be on while the buttton is pressed, otherwise (button not pressed) LED 2 is on?
    This makes a big difference.
     
  3. bigjayman

    bigjayman

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    Feb 3, 2013
    The latter. LED 1 is on when button is pushed, when the button isn't being pressed LED 2 is on
     
  4. Harald Kapp

    Harald Kapp Moderator Moderator

    11,513
    2,651
    Nov 17, 2011
    Calculate resistors as required for your operating voltage and LED operating point.
    Without further comment:
    [​IMG]
     

    Attached Files:

  5. bigjayman

    bigjayman

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    Feb 3, 2013
    Thank you so much. Works perfectly. You are my hero.
     
  6. genifis

    genifis

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    May 13, 2018
    Why not find a SPDT switch with the dimensions you need?
     
  7. AnalogKid

    AnalogKid

    2,501
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    Jun 10, 2015
    1. This thread is over 5 years old.

    2. This can be done with no transistors at all:

    1 resistor to limit the current to *both* LEDs
    1 small diode
    1 SPST switch

    ak
     
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