# Digital Clock with Logic Gates

Discussion in 'The Projects Forum' started by kimbo0o, Dec 7, 2008.

1. ### kimbo0o Thread Starter New Member

Dec 4, 2008
4
0
Hello,

This is my last lab so it is the most difficult. I need to write down my logic and the gates used to reconfigure my two 7-segment display to operate as the hours used in a digital clock. So far I have an AND gate being used as the minutes which goes up to 59 and my logic for that is fine because it's only one AND gate. I am lost as to what to use to get one 74193 to stop @ 13 and the other to stop at 1, both need to be reset to 00. I hope this isn't too confusing because I finally understand it all after an entire semester working with these logic gates.

2. ### beenthere Retired Moderator

Apr 20, 2004
15,815
283
Your post is a bit hard to follow. AND gates usually don't get used as counters. They might be used to tie to counter outputs such that they generate a MR signal when one counter is a 1 and the other is at D.

How do you go from the '193's binary value to the BCD to drive the display? What IC do you use for the display driver?

3. ### Wendy Moderator

Mar 24, 2008
20,772
2,540
Lets go through the sequence...

12 Hour clock; 01 02 03 04 05 06 07 08 09 10 11 12

24 Hour clock; 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23

Which one do you want to use?

You beat me this time BT.

4. ### kimbo0o Thread Starter New Member

Dec 4, 2008
4
0
The AND gate is tied to the outputs, I am using two 74193 4-bit COunters each with 7447 BCD-to-seven-segment decoder/driver. on 74193 + 7447 is used as the tens place, the other 74193 + 7447 as the ones place. One is connected to a multivibrator, the other is connected to that(74193+7447).

12 hour clock.

Thanks for getting back to me so quickly

5. ### Wendy Moderator

Mar 24, 2008
20,772
2,540
I would seriously consider using something like a 7473 Dual JK FF. The reason is you can set the logic up a lot easier, a simple AND gate will do it with 5 of these flip flops. Three chips total.

You can do it with the 74193, but it will require more logic (I think). You'll only need one, just use a single flip flop (or a dual) for the 10's place counter. Still need 3 chips from what I can see.

Last edited: Dec 7, 2008
6. ### kimbo0o Thread Starter New Member

Dec 4, 2008
4
0
I have to use the 74193, stated in the assignment. Do you know what logic to use with the gates?

7. ### Wendy Moderator

Mar 24, 2008
20,772
2,540
OK, as a homework assignment we can't spell it out directly (an informal but firm policy here at AAC), but we can provide strong hints. Think about feeding the new value into the inputs (the "01") when the counters hit "13" (another hint, only 3 bits are high with that number, so we're talking a 3 input AND gate). Post the schematic you have so far and we can point out where the problems might be.

8. ### beenthere Retired Moderator

Apr 20, 2004
15,815
283
One more reminder. The 7447 takes BCD as an input. The 74193 outputs binary values. How do you manage to get the display to track the count? 59 decimal is 3A hexidecimal.

9. ### Wendy Moderator

Mar 24, 2008
20,772
2,540
I think the OP is using two 74193s, they can be configured quite easily. There is a CMOS varient (totally different number) that I'm fond of, only reason I think so. Each 74193 is a BCD counter. Wasteful, but this is homework after all.

10. ### beenthere Retired Moderator

Apr 20, 2004
15,815
283
My TTL data book indicates that the 74192 is BCD, the '193 is binary.

11. ### Wendy Moderator

Mar 24, 2008
20,772
2,540
I think we are at the point where the OP has to post his schematic for us to be able to continue. You think?

12. ### beenthere Retired Moderator

Apr 20, 2004
15,815
283
Shooting in the dark, otherwise.