# how to design a 30 second counter?

#### toyota8

Joined Oct 26, 2008
8
how to design a 30 seconds counter using jk flip flops? i can only do a 31 seconds counter.

#### beenthere

Joined Apr 20, 2004
15,819
You add external gates like AND gates to sense the count of 30 (1Eh). Take a look at a decade counter to see how they roll over at 9 instead of F.

#### hgmjr

Joined Jan 28, 2005
9,029
You might be able to preload the 5 F/Fs with the value 1 on overflow instead of resetting them to zero. That way your count would start from 1 instead of 0. That would give you a 30 count.

hgmjr

#### toyota8

Joined Oct 26, 2008
8
Thanks for the advice, but the problem is I am doing a 30 seconds synchronous countdown. I did simulation in Digital Works but it didn't turn out well. How can i make Q0=1, Q1=Q2=Q3=Q4=1, means it will start from 00001 instead so the NOT will b 30, cuz wat i did was attaching Q bar to the decoder.. If anyone can provide me a simple .dwm file or a picture of the circuit diagram, I would be thankful. Any links with info similar ti these questions are also helpful. Thanks a lot I have tried, and tried and u people r my only hope.. Bless.

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#### beenthere

Joined Apr 20, 2004
15,819
Perhaps you could post up your logic diagram so we can see what you have got working.

#### toyota8

Joined Oct 26, 2008
8

Here's the diagram. Not sure what went wrong. Thanks

#### toyota8

Joined Oct 26, 2008
8
another thing that i would like to know is that how can we display a two digit number using two seven segments. Like when it goes from 9 to 10, both the seven segments should light up as 1 and 0, etc. Using a single seven segment connected to the BCD decoder i could only display numbers up to 9. Can anyone teach me what is the way to utilise two seven segment displays? Thanks...

#### beenthere

Joined Apr 20, 2004
15,819
Think of two counters, two display drivers, and two displays.