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switching help please!!!

Discussion in 'General Electronics Discussion' started by fish763, Nov 30, 2012.

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  1. fish763

    fish763

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    Nov 30, 2012
    i have a very basic circuit and would like to modify the fuctionality of it.

    There is more to it than this but i am trying to keep it simple;
    I have two LED arrays lets call them LED 1 and LED 2, I also have two on/off switches lets call them SWITCH A and SWITCH B ossolates on and off. Both LED arrays share common ground with a power source of 12VDC.

    How i would like it to work;
    Switch A on switch B off; both LED 1 and LED 2 are on
    Switch A on and Switch B on; LED 1 is on and LED 2 on and blinking
    Switch A off and switch B on; LED 1 is off and LED 2 on and blinking

    Basicaly switch B operates LED 2 reguardless of what switch A is doing.

    thanks in advance
     
  2. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    May 8, 2012
    Are you familiar with the 555 timer and logic gates?

    Chris
     
  3. fish763

    fish763

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    Nov 30, 2012
    Yes but I have only used them as a clock source not sure how to use it to control on and off?
     
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    You've not said what happens if both switches are off. Presumably both LEDs are off?

    edit: if that is true, switch 1 turns LED 1 on and off, and switch 2 connects and disconnects LED 2 to the output of a 555 (the 555 set up to give a reasonable flash rate)
     
    Last edited: Nov 30, 2012
  5. fish763

    fish763

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    Nov 30, 2012
    When both switches are of both LEDs are off yes. Switch Bs source is allready on a pulse from a different circuit. I just need to disable switch As input when switch B is closed.
     
  6. fish763

    fish763

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    Nov 30, 2012
    I was thinking maybe a logic gate but I'm not sure.
     
  7. fish763

    fish763

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    Nov 30, 2012
    Okay, logic gate thanks Chris. Sorry I was distracted and missed part of your post. Centurylink ported one of my external IP blocks to a different customer and I had to fight to get them back.
     
  8. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    Sorry, I misread this one

    You need to draw a truth table with 3 inputs A, B, and C; and 2 outputs L1 and L2.

    there will be 8 combinations from 0 0 0 to 1 1 1. C represents the flashing signal which should be copied to the L2 when its flashing

    like this

    A B C | L1 l2
    0 0 0 | 0 0
    0 0 1 | 0 0
    0 1 0 | 0 0
    0 1 1 | 0 1
    1 0 0 | 1 1
    1 0 1 | 1 1
    1 1 0 | 1 0
    1 1 1 | 1 1

    Then figure out the logic required

    L1 = A is the first obvious relationship.

    L2 = (B and C) or (A and not B)
     
    Last edited: Nov 30, 2012
  9. fish763

    fish763

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    Nov 30, 2012
    Look at it this way. I have two LEDs and two switches, the 12VDC source for switch A is constant and the 12VDC source for switch B is pulsed. When switch A is closed and B open both LEDs are lit and steady. When switch A is open and switch B is open LED 1 is constant and LED 2 is pulsed.

    The biggest issue I have with using a logic gate is the fact that the source for switch B is pulsed so the logic gate will see switch B as open close open close. And I am note sure how to compensate for that and prevent switch A from providing power to LED 2. Basically I think LED 2 will just stay on and not pules.
     
  10. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    L1 = A is the first obvious relationship.

    L2 = (B and C) or (A and not B)
     
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