Digital Clock Design

Discussion in 'Homework Help' started by bryanbluesky, Nov 17, 2007.

  1. bryanbluesky

    Thread Starter New Member

    Nov 17, 2007
    2
    0
    Hi,

    I'm a new user here. I am juz a first year student who starts learning digital design.

    As my project, I did a digital clock using 7490 IC. I use two 7490 decade counters to create divide-by-10 counter and divide-by-6 counter so that I could get a divide-by-60 counter. The counter has no problem and counting properly. But the problem lies in resetting the digits to 0 0. I cannot reset the counter and it starts counting from random digit. So how can I reset the counter?

    After I got first Seconds Counter, I try to connect it with another divide-by-60 counter for Minutes counting. I connect the output of the first Seconds counter and the clock of the Minutes counter. I also find problem in resetting the time for the Minutes counter.

    If anyone can help, I'm looking forward to your advice. =)

    ~sky~
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    You need external logic. To reset at 60, the condition is that the lower-order counter outputs are all 0. The upper counter has to have Q0 & Q3 set with Q1 & 2 reset. When that condition exists, it puts a 1 in at pins 2 & 3 to reset the counter to zero.

    A four input NOR will have a 1 out when all inputs are 0. A two input NOR will have 1 out when both inputs are 0. An AND gate will have 1 out when both inputs are 1.
     
  3. bryanbluesky

    Thread Starter New Member

    Nov 17, 2007
    2
    0
    Thanks a lot for your help.

    Now my counter is working properly from 00:00:00 to 23:59:59.

    Yet, one more thing, I cannot try to solve is, how to set the time to a particular one. E.g. 04:23:56 . Is there any way of doing this ? I just need to set a particular time for my clock to start working on.

    I rily admire your help. Thanks.

    Looking forward for more advice.

    ~sky~
     
  4. recca02

    Senior Member

    Apr 2, 2007
    1,211
    0
    for that you will have to input the equivalent binary code to the preset terminals of ff.
     
  5. GS3

    Senior Member

    Sep 21, 2007
    408
    35
    Normally this is done by advancing the time rapidly rather than setting it directly to a certain time. Normally you have a "fast" and a "slow" advance button. All you need to do is input a higher frequency which means maybe inputing 50 hz instead of 1 Hz to the counter.
     
  6. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Since your counters do not have parallel load inputs, your only way out is going to be to generate a faster clock - 2 or 3X - and be able to apply it to the various counters - hours, minutes, and possibly seconds, if you display seconds.
     
  7. karate2012

    New Member

    Jun 8, 2008
    2
    0
    thanx for the programme
     
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