need with my project(its only basic gates)

Discussion in 'The Projects Forum' started by Adv.Logic, Dec 12, 2010.

  1. Adv.Logic

    Thread Starter New Member

    Dec 4, 2010
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    Last edited: Dec 12, 2010
  2. Wendy

    Moderator

    Mar 24, 2008
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    2,536
    Welcome to AAC!

    If either of the S/R flip flops you have made are set, then that is where they stay. The output will go high if either is high. How are you planning to reset them? There is also no way to make sure they go low on the initial condition, they could swing either way on power up, which will put the output at a permanent high state.

    [​IMG]
     
  3. Adv.Logic

    Thread Starter New Member

    Dec 4, 2010
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    0
    I plan to make a circuit that when either of the two buttons will push the led will light up. I try only one r/s flip flop with a led on the output and when I push the pushbutton the output will go high but when I make that circuit then or gate their output it doesn't work.
     
  4. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    be sure the chip is a logic family that can drive a 10 or 20 milliamp LED. CMOS might not be able to light a LED without using a buffer/driver/inverter.

    Detecting a high(5 volt) with a meter does not mean it will be able to drive high current(low impedance) components tied directly to its output pin.

    CHECK THE DATA SHEET FOR MAX CURRENT RATINGS of the chip sets you are using.
     
  5. Wendy

    Moderator

    Mar 24, 2008
    20,765
    2,536
    An easy fix...

    [​IMG]

    You need to initialize the S/R flip flops at power up as I suggested. Something like this...

    [​IMG]
     
    Last edited: Dec 12, 2010
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