How to set up a mod 24 count up using 74193 binary counter?

[songokujames]

I m using 2 7-segments displays, 2 74193 binary counter and 2 7447. I want to count from
0 1 2 3 4 5 6 7 8 9 10 11 12 13....23 then back to 0. I only manage to count from 00-29. Anyone can help me? And I cant use any other counter because my project only allow me to use the above components.

 

[ccurtis]

Are you sure you are supposed to use 74193 and not 74192? The 7447 is a BCD to 7 segment decoder, but the 74193 does not count in BCD. The 74192 counts in BCD. Even then, I don't think a mod 24 count can be done without the addition of gates, not listed in your allowed components, because nothing uniquely happens when the 24 or 25 counts are reached that doesn't happen at lower counts to preset or reset the counters. Nothing I can think of anyway. Maybe someone else here has an idea. I'd be interested in it.

 

[songokujames]

Sorry, I dint post correctly, counter is fixed but I still can use addition gate like OR, AND,NOT gates but I just dint know how to use the gates to get it count 00-24.

 

[ccurtis]

If you are using the 74193 and can count to 29 and have it display properly, then you must have figured out how to use external gates to get the lower counter to reset at 10 binary. Just use the same idea using gates to, additionally, reset both counters simultaneously when you have 5 on the lower counter and 2 on the upper counter. Like when Q1 on the upper counter is high and Q2 and Q0 on the lower counter are both high.

 

[songokujames]

It dint display correctly if I reset both counter simultaneously. It show that it still count from 1-16 at the lower counter then it carry in to the upper counter. So , overall for the upper counter it count from 0-2, but the lower count from 0-15,1-15 then 0-4 . I cant get it reset at 10 if I connect both reset simultaneously.

 

[Diver300]

The easiest way to limit a counter is to reset when the count is too big, so you need to reset the lower 74193 when it gets to 10.

You also need to reset both of the 74193s when the count gets to 24.

This circuit should work:-

View attachment 63160

The 2, 4, 8 and 20 are the outputs of the 74193s that represent those values. The RU is the reset for the 74193 that represents units and the RT is the reset for the 74193 that represents the tens.

 

[songokujames]

but how can I get 20 outputs for 74193? I thought the max value is 15?

 

[Diver300]

There are two 74193s. The lower one represents the units, and its outputs represent 1, 2, 4 and 8. The upper one represents tens and its outputs represent 10, 20, 40 and 80. I labeled the diagram using that convention. The lower counter is reset whenever the outputs representing 8 and 2 both go high, which is when is shows 10, so it will only show 10 for a few microseconds before showing 0.

When the total count gets to 24, both counters are reset.

I realise that if you are counting 0 - 24, the upper counter never gets beyond 20, so the two outputs representing 40 and 80 should never operate.

 

[songokujames]

I try it but it seem only te lower counter work and count from 0-9 but the upper one count at all. I connect the carry out from lower to up pin in upper counter.

 

[Diver300]

The lower counter will produce a pulse on the carry out pin when it rolls from 15 - 0. As you reset it whenever you get to 10, it never gets to 15 so it never carries.

You should connect the "count in" pin of the the upper counter to the reset line of the lower counter.

 

[xylenet]

hey can anyone help me out of here. i want to create a 24second shotclock but the problem is my clock starts at 99-00 but its adjustable to 24-00 though its not feasible. i wanted a 24 shotclock with at least 2 switches (pause and reset). i could give the simulation on how far i have gone through email. im using livewire as a simulator, is anyone interested on giving me a hand. oh btw i used 555, 74192 and 7447 as my ICs