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Homework Help: CLD Digital Clock

  1. Apr 28, 2012 #1
    1. The problem statement, all variables and given/known data

    I want to make a digital clock on hardware using 555 timer and BCD decoder to 7 segment display. Can anyone help me about the circuit ?

    2. Relevant equations

    3. The attempt at a solution

    I am using the concept to increment the input of BCD decoder with the help of 555 timer but dont know how to do so
  2. jcsd
  3. Apr 28, 2012 #2
    Do you mean a 24 hour clock that tells human time or a 7-segment display that goes 0-9 and repeats?
  4. Apr 28, 2012 #3


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    You would need a BCD counter between the 555 and the decoder.

    The 555 would connect to the clock of the BCD counter and the output would be converted by the decoder into drive for the 7 segment display.
  5. Apr 29, 2012 #4
    @antiphon : I want to make a 7 segment display that goes 0-9 and repeats .... and for hours , minutes as well as seconds ......
    @vk6kro : how to increment the counter that runs the clock ?
  6. Apr 29, 2012 #5


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    The counter will increment on each rising edge of the square wave from the 555.

    So, you can arrange the incrementing rate by adjusting the oscillation frequency of the 555. (you do this by selecting the components that determine the frequency. Making both resistors 470 K and the capacitor 1 uF will get a frequency of about 1.02 Hz)

    If you are trying to make this look like a real clock, don't forget that the seconds and minutes counters will go to 59 and then to zero, and the hours counter will go to 12 and then to one.
  7. Apr 30, 2012 #6


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    Staff: Mentor

    You are not going to get a very accurate clock circuit using a 555 timer chip. A better solution would be to use a CD4060 or 74HC4060 IC and a 32.768kHz watch crystal. Here is a simple Google search that includes circuit info and a YouTube video:


    Last edited: Apr 30, 2012
  8. May 1, 2012 #7
    Thanks alot ...... I got the solution ......
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