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Why doesn't my shift register work?

Discussion in 'General Electronics Discussion' started by leonheard, Dec 31, 2014.

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  1. leonheard


    Jan 25, 2013
    why my shift register doesnt work?!


    I bought an TC74HC595P (Toshiba) 8 BIT register... the datasheet:

    i want to use it without a microcontroller all with switch buttons ( for educational purposes only doesnt need to work 100%) since i am very interested in learning about serial to parallel data in "real time".

    like in this tutorial video:

    this is my schematic:

    it doesnt work like it suppose to work, it gives me random outputs! :/

    is something wrong with:

    my schematic?
    IC ?

    i tried to fix this for 19 hours now and nothing :(
    i would appreciate your help...

    thanks! :D
  2. Laplace


    Apr 4, 2010
    Try shorting out the LED's on the input pins. The voltage drop on the LED may be preventing the input from getting a low enough voltage to be a logical ZERO.
    Arouse1973 likes this.
  3. leonheard


    Jan 25, 2013
    thanks for your help! i made a simple monostable vibrator with an ic555... now my shift register WORKS 100%!:p i hope this helped someone else with same problem...
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