# 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.

~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.

~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