can any one till me

Discussion in 'General Electronics Chat' started by abuarab88, May 28, 2009.

  1. abuarab88

    Thread Starter Member

    Nov 6, 2008
    19
    0
    hello all<

    can any one tell me what does this circuit do, single part of it
    it is adigital clock cct
    [​IMG]
     
  2. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    The capacitor values for the 555 oscillator are much too low and it will not work.
    The datasheet shows 1000pF as a minimum value.

    I think the values of R3 and R4 are much too low and cause the 4511 ICs and LED displays to burn.
     
  3. abuarab88

    Thread Starter Member

    Nov 6, 2008
    19
    0
    thanks
    but the cct works properly
    i need to know the basic work>>>
    how does it work
    purpose of the ic's
     
  4. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    The logic is wrong, too. While labeled as 74LS93, the counters have the pinouts of 74LS90's.

    A digital clock has to be able to count higher than that circuit. Minutes and seconds need counts of 0 - 59, hours 1 - 12.
     
  5. Papabravo

    Expert

    Feb 24, 2006
    10,142
    1,790
    If the circuit wa designed and implemented correctly, which it is not.
    The 555 should be configured as an astable multivibrator whose purpose is to generate a square wave at some convenient frequency. The counters will count rising edges of the 555 output and the 4511 is a BCD to 7-segment decoder.

    This circuit would only work in some parallel universe, or there are details of which you and we are not aware.
     
  6. bertus

    Administrator

    Apr 5, 2008
    15,648
    2,346
    Hello,

    The 555 has to low value capacitors.
    The two counters will count until 9.
    So the circuit will count 0 - 99.
    The resistor for the led is to low and you shpuld use resistors for each segment (not the complete display).

    Greetings,
    Bertus

    PS in simulation it may look to work, but practice is different.
     
  7. radiohead

    Active Member

    May 28, 2009
    474
    31
    the 555 is a poor choice for an accurate clock circuit anyways. For accurate timing, you would need a crystal controlled oscillator.
     
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