Circuit Noise

Discussion in 'The Projects Forum' started by yasir_66, Jul 1, 2009.

  1. yasir_66

    Thread Starter Active Member

    Jun 25, 2009
    71
    1
    I am having problem with my counter.
    I works proper but when i hold it in hand then it becomes working when i place it on a table or anything it starts counting itself.
    whats the problem?
    plz help me
     
  2. bertus

    Administrator

    Apr 5, 2008
    15,635
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    Hello,

    Can you post a schematic?

    Greetings,
    Bertus
     
  3. yasir_66

    Thread Starter Active Member

    Jun 25, 2009
    71
    1
    this is the schematic
     
  4. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    It appears that you have left the COUNT and RESET inputs "floating".

    All CMOS inputs must be tied to either Vdd or ground, or problems like this can occur.

    You could use individual 10k resistors from the COUNT and RESET pins to ground to avoid this problem.
     
  5. yasir_66

    Thread Starter Active Member

    Jun 25, 2009
    71
    1
    i have added 555 clock to pin#12(count) & reset to vcc through 10k.
    i still have problems like that.
    help me plz
     
  6. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    It might help things if you place another 0.1uFd bypass capacitor very close to the positive voltage terminal on the 4-bit counter.

    Check your wiring. You need to keep interconnectin wires as short as plausible.

    hgmjr
     
  7. yasir_66

    Thread Starter Active Member

    Jun 25, 2009
    71
    1
    ok SIR ill inform u after following u.
    thnx
     
  8. yasir_66

    Thread Starter Active Member

    Jun 25, 2009
    71
    1
    hello SIR,
    I followed u & i added 0.1uf to the 4bit counter(14553) on vcc but i am suffering same problem.
    plz help me
     
  9. bertus

    Administrator

    Apr 5, 2008
    15,635
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    Hello,

    Do you also have a 0.1 uF capacitor on the power lines of the NE555?
    Is there a 0.1 uF capacitor on pin 5 (control voltage) to ground of the NE555?

    Greetings,
    Bertus
     
  10. yasir_66

    Thread Starter Active Member

    Jun 25, 2009
    71
    1
    no sir i left 555's pin#5 floating
     
  11. yasir_66

    Thread Starter Active Member

    Jun 25, 2009
    71
    1
    Sir i connected vcc & pin#4 to the sensor(optocoupler).
    i placed 22uf on pin#2 & 6
     
  12. yasir_66

    Thread Starter Active Member

    Jun 25, 2009
    71
    1
    i observe that whenever i touch any soldering point my counter becomes normal & when i dnt touch then i becomes abnormal & counts itself.
    what does it mean of touching my finger to any soldering point?
     
  13. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    A 555 oscillator causes 400mA current spikes on its power supply. That is enough to kill any counter circuit operating off the same supply.
     
  14. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    You affect the parasitic capacitance and leakage resistance of the circuit.

    Post your circuit.
     
  15. bertus

    Administrator

    Apr 5, 2008
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  16. yasir_66

    Thread Starter Active Member

    Jun 25, 2009
    71
    1
    so what should i do for making circuit normal?
    what's the relation of my finger with circuit?
     
  17. yasir_66

    Thread Starter Active Member

    Jun 25, 2009
    71
    1
    this is the schematic;
    what is the relation of my finger with circuit such that when i touch it becomes normal?
    help me plz:)
     
  18. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    Greetings yasir_666,

    I have merged all your related and scattered threads into the original thread.

    In the future, please keep related replies and requests for information in the same thread. Splitting them up into multiple threads makes it hard for those members following the thread to keep track of the discussion.

    Thanks,
    hgmjr
     
  19. yasir_66

    Thread Starter Active Member

    Jun 25, 2009
    71
    1
    ok thnx hgmjr
     
  20. bertus

    Administrator

    Apr 5, 2008
    15,635
    2,342
    Hello,

    Can you post a photo on how you have build you counter?
    The touching behavour can be related to the way you made it.

    Greetings,
    Bertus
     
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