cd40110 counts in big steps

Discussion in 'The Projects Forum' started by doctortropico, Aug 8, 2013.

  1. doctortropico

    Thread Starter New Member

    Aug 4, 2013
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    0
    Hi all,

    I tried to build a simple up/down counter using two 7 segment displays and two CD40110's. I mainly followed the schematic in attachment(mainly being: for now I only added an up-button, down and reset are wired to the neutral, I also didn't use the 555-timer as a clock)

    Whenever I push the button, the counter counts in bigger steps than just +1.
    I also notice it (sometimes) counts up when I release the button.
    Here is a little video: http://www.youtube.com/watch?v=PaAdTANoeWM

    I have rebuilt this four or five times, but I can not seem to get rid of the problem.

    Any thoughts on what could be wrong?
    Thanks.
     
  2. bertus

    Administrator

    Apr 5, 2008
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  3. doctortropico

    Thread Starter New Member

    Aug 4, 2013
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    Thanks Bertus, I'll give it a read.

    I tried different switches, but all with the same problem. Now I know why.
     
  4. Dodgydave

    AAC Fanatic!

    Jun 22, 2012
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  5. Mussawar

    Member

    Oct 17, 2011
    68
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    A mechanical switch, whenever pressed, will produce a countless pulses which are enough to trigger the 40110 many time resulting undesired results. You need a switch de-bouncer. Please see the attachment. This circuit is working fine fir me in my recent prefect. It will produce a neat and clean pulse. You may change values of R1 and C1 to get desire time period since there is a difference bw simulation and real circuit working.
     
    Last edited: Aug 9, 2013
  6. doctortropico

    Thread Starter New Member

    Aug 4, 2013
    3
    0
    Thanks to all.

    Someone gave me a device called a snubber. It works ok most of the time now, but occasionally still counts in steps of two.

    I will try this debouncer using the 555 timer.
     
  7. MrChips

    Moderator

    Oct 2, 2009
    12,452
    3,371
    Switch bounce needs to be a sticky. It comes up time and again.

    The preferred solution is to use a double-throw switch as shown in the first circuit.

    For a SPST switch, try the second circuit:

    [​IMG]
     
  8. ramancini8

    Member

    Jul 18, 2012
    442
    118
    The common S/R flop solution has one problem because if the first bounce does not contain enough energy to change the flop state it will relax back to its initial state while issuing a partial pulse to the logic that might or might not act.

    Without a resistor between R3 and C1 there is potential for capacitor dielectric absorption to cause an error. Often a diode is paralleled with the resistor to speed up charge time.

    Admittedly, these are esoteric errors, but they happen.
     
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