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74LS193 Glitches

Discussion in 'General Electronics Discussion' started by Mirceam94, Mar 13, 2011.

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  1. Mirceam94


    Dec 17, 2010
    I'm using the outputs of a 74LS193 (binary counter) to drive some control circuitry in a project of mine, but I'm having some problems with reliability. The IC tends to count twice for every clock pulse, and sometimes it completely ignores incoming clock pulses. And other times it just skips around randomly... I've breadboarded the same circuit, and have had no problems with it in the same configuration. I've been trying to fix this problem for weeks now, with no luck. Can you guys help me?

    Some more info: The clock circuit is two inverters connected head-to-tail, with a simple RC network maintaining a 1Hz pulse rate. The output (inverters are in a 74LS04 package) is fed into a Schmitt trigger (74LS14), and then into the 74LS193 'Up' input. I've checked the datasheets over and over again, and it seems everything should be working fine. I have de-coupling caps installed, all of the necessary signals on the '193 are pulled to their corresponding positions for the IC to count up, but no luck.

    Also, I don't have a schematic drawn up for this circuit, so please don't ask for one. The connections are extremely straightforward. By the book, literally -> I've connected all signals present in the datasheet to where they need to be. Specifically...

    LOAD -> High
    CLR -> Low
    DOWN -> High
    UP -> Schmitt trigger output

    Thank you in advance!
  2. davenn

    davenn Moderator

    Sep 5, 2009
    well it would help to draw a cct :) then we mite be able to give guidance on where you may be going wrong, a good sharp pic of the layout on the board would probably be of aid as well :)

  3. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    Agree 100% with davenn.

    I would be thinking along the lines of one or more of the following:

    1) ground bounce
    2) switch debouncing
    3) slow clock transitions
    4) power supply noise

    1 and 4 are somewhat related. If you're not switching your main load when it's breadboarded then these are real possibilities.
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