# 12 hours TTl clock

#### chochinooo

Joined Sep 24, 2011
6
hi I'm trying to construct a 12 hour digital clock without the use of micro controllers. I tried this virtual diagram I found from tutorials and samples but its not working properly for me, maybe I got some things wrong..I do really need help about this..thank you..pls do enlighten me and use simple words because I'm just a beginner on this.I attached the schematic diagram I'm working on

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#### Wendy

Joined Mar 24, 2008
22,138
I don't have time to do a detailed analysis, but those displays are going to need current limiting resistors, 7 resistors per display.

I am currently designing a CMOS clock for the AAC book. I am getting by without resistors due to how the CMOS chips work, but I am uncomfortable with it.

Digital clocks

Another good resource that has a working schematic of a TTL clock using different chips is Bill Bowden's website.

Bill Bowden's Hobby Circuits

Personally I think you're biggest mistake is trying to do it all at once. Break it down, do the seconds, then the minutes, then the hours, and try to understand the small pieces first.

#### SgtWookie

Joined Jul 17, 2007
22,210
As Bill mentioned, you need resistors in each wire, A through F of the 7-segment displays. 330 Ohms will probably be about right.

Your LED1 needs a current limiting resistor also. You'll get better results if you use the TTL output to sink current from the LED than to source current to it.
Disconnect LED1 from both ground and U21A. Then connect the cathode of LED1 (what is now the right-hand terminal) to the same pin of U21A. Connect one end of a 220 Ohm resistor to the anode of LED1, and then connect the other end of the resistor to Vcc.

For D1, use a Schottky barrier diode instead, like a 1N5817 thru 1N5819, BAT54, something like that. Schottky diodes are extremely fast switching, and have a very low Vf compared to standard silicon diodes.

On U3, you don't have pins 1 and 4 connected to Vcc, just pin 5.

Remove R1 and R2. If you want to use pull-up resistors, then use one 330 Ohm to 470 Ohm resistor per input to Vcc.

#### chochinooo

Joined Sep 24, 2011
6
I finally got what's missing,..I can get the seconds and minutes working but the minutes only works until 9,after 9 mins it would not display 10 rather displays 00..thank you so much for helping me..the replies are such a big help..

#### chochinooo

Joined Sep 24, 2011
6
anyways here's my current diagram.

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#### SgtWookie

Joined Jul 17, 2007
22,210
Well, your seconds work correctly, right?

And your minutes only counts to 9, right?

You tell me what is the range of counting for seconds, and what is the range of counting for minutes?

What differences are needed between the seconds counting and the minutes counting?

#### chochinooo

Joined Sep 24, 2011
6
Well, your seconds work correctly, right?

And your minutes only counts to 9, right?

You tell me what is the range of counting for seconds, and what is the range of counting for minutes?

What differences are needed between the seconds counting and the minutes counting?
yes you're right. I got the seconds working right.
seconds should count 0-5tens, 0-9 units ->60seconds
minutes should count 0-5tens, 0-9 units ->60 seconds

did I connect/ use something that shouldn't be there?

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#### Wendy

Joined Mar 24, 2008
22,138
The minutes and seconds counters should be virtually identical, they do the same thing.

#### SgtWookie

Joined Jul 17, 2007
22,210

It's a lot more rewarding to figure it out yourself than to have someone else hand you the solution.

You're going to run into a snag with the hours digit, as it starts off with 1 instead of 0.

#### chochinooo

Joined Sep 24, 2011
6
yes.. the hours will be a big challenge.. I'll figure out the minutes first as to why it was giving me that output.. thank you so much for your help. BIG thanks

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#### chochinooo

Joined Sep 24, 2011
6
alright..so here I am again..I was actually still doing this project of mine..I got minutes and seconds working right and I got hours work as well but there's still something wrong..when the hours reaches 12 it was supposed to reset and be 01:00 but it doesn't it actually has an output of 13 for a short period of time then jump to 19 after 19 it reset back to 00..this was logically challenging.. can anyone help??..I attach schematic for hours part only.

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#### SgtWookie

Joined Jul 17, 2007
22,210
You have more of a problem than that.

What's the count sequence for the hours?
Better write it down, in a column.
Then write the binary representation next to the columns.

You also have a problem in the vicinity of D1. If the input to D1 is high, and U15 pin 11 is low, you will have a high current flow via D1.
U7A's inputs aren't correct.