LED switch

Discussion in 'The Projects Forum' started by Brian Krupicka, Nov 1, 2014.

  1. Brian Krupicka

    Thread Starter New Member

    Nov 1, 2014
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    I have a need for a simple SPDT type switching system to power LED’s on a signal bridge for my model railroad.

    12V DC input and 12VDC on/off output 1 and 12VDC off/on output 2.

    Any assistance would be helpful.
    Brian
     
  2. Dr.killjoy

    Well-Known Member

    Apr 28, 2013
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    What do need assistance for ??? You make the center tap +12 and the right side use one row for on and the other is off .. The left side do the same but opposite..
    Just remnber the current limiting resitors for the LEDs
     
  3. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
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    LED Switch.png Like this?
     
  4. Brian Krupicka

    Thread Starter New Member

    Nov 1, 2014
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    I do not want to use a switch or relay contacts. I would like to use an IC or transistor circuit as the switch.
     
  5. Dr.killjoy

    Well-Known Member

    Apr 28, 2013
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    Please explain what you want cause we are trying to help and you are changing your mind and making this very difficult..
     
  6. Brian Krupicka

    Thread Starter New Member

    Nov 1, 2014
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    I would like a circuit that:
    When you have 12VDC on the input, output one would be on and output two would be off
    When there is no 12VDC on the input, output one would be off and output two would be on.
    Normal SPDT type swicthing but using transistors or IC's not relay contacts or standard switches.

    Brian
     
  7. ScottWang

    Moderator

    Aug 23, 2012
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    For the current maybe some resistors and transistors need to change.

    One12VTwoOuput_Brian Krupicka_ScottWang.gif
     
    absf likes this.
  8. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
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    What's controlling the presence or absence of 12VDC to this circuit? If 12VDC is absent. what is the input connected to?

    How many of these LEDs are you going to light in total?

    Is 12VDC the only power source available? What is supplying the power (e.g., is it a DCC power supply, booster or traditional model RR power pack)? How much current can it supply?

    There are several ways to accomplish this, but we need to know more about the environment. If you could answer the above questions, adding as much detail as possible to cover the questions I might ask...
     
  9. Brian Krupicka

    Thread Starter New Member

    Nov 1, 2014
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    thank you Scott
     
  10. Brian Krupicka

    Thread Starter New Member

    Nov 1, 2014
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  11. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
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    Another way, using ICs, is to use flip flops. In particuar, a toggle or T flip flop.

    The schematic below uses a JK flip flop from a CD4027 package, wired as a T flip flop. The input is split on the left, one branch going to the J input and a second going to an inverter from a CD4049 package and then to the K input. This is how to make a T flip flop from a JK flip flop. Clock, Preset and Clear are all unused and tied to ground.

    The Q and Q bar outputs are your toggling signals. The IC can't source/sink enough current to light the LEDs, so we use an NPN transistor buffer.

    This circuit is presented as is, as I cannot test it right now. But you should be able to get some ideas from its construction. Note that each CD4027 package contains two flip flops and the CD4049 package contains 6 inverters.

    model-rr.png
     
    absf likes this.
  12. ScottWang

    Moderator

    Aug 23, 2012
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    About two years ago that I designed the similar but a little different circuit used two methods, one was bjt and another one was just used one 74LS05, as the circuit that I attached, it needs to use 74LS05 to replacing the 3 bjts circuit.
     
  13. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
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    Remember his circuit must operate in a 12VDC environment. The 74lsxxx series don't have a broad enough operating range, which is why I went with the CD4000 series.
     
  14. ScottWang

    Moderator

    Aug 23, 2012
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    It just needs a resistor and a zener to do.
     
  15. Brian Krupicka

    Thread Starter New Member

    Nov 1, 2014
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    thank you all for your assistance.
    Brian
     
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