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Preventing a 4013 'Setting' on Power Up

Discussion in 'General Electronics Discussion' started by PastySmuggler, Dec 8, 2011.

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  1. PastySmuggler


    Dec 3, 2011
    Hi folks!

    I'm using a 4013 to take a push button input to start a motor (driven through a BC107 transistor). The Q O/P also switches on an I/R photo interrupter. When the motor turns, a paddle will break the interrupter beam. This output generates a rising edge which is connected to the clock input of the 4013 and resets it, switching the motor off.

    All this works - BUT! Because the clock input has a pull-up resistor, it always sets the FF on power up. I want to stop this happening, but can't think of a way of doing this without putting in a reset switch!

    Does anyone have any ideas?

  2. jackorocko


    Apr 4, 2010
    Steve taught me this trick, Use an RC circuit to keep the clock input low for a few (m)seconds after initial power-up. It might help to see a schematic of what you have.

    The 4013 has a set pin, are you using this pin at all? again a schematic of what you have would help
    Last edited: Dec 8, 2011
  3. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    In this case. probably pull the set or reset pin (whichever is appropriate) high via an RC during power up.
  4. PastySmuggler


    Dec 3, 2011
    Many thanks for those ideas. I've actually solved the problem myself - the 'how' in a mo!

    Yes - I'm using the 'set' input for the input from the push button switch. The 'clock' input is used to reset the FF when the paddle interrupts the IR sensor!

    It occurred to me that, since I only ever use the clock pulse to switch the Q output off (it's set ON by the switch to the SET input), instead of linking the QBar O/P to the Data I/P (the cause of my problem!), if I tied the Data I/P low, any clock pulse will always try to turn the Q O/P off! Tried this evening - and it works a treat!

    Many thanks!!
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