Introduction: 12 Hour TTL Clock

Picture of 12 Hour TTL Clock
This was the final project for my Digital 2 class it was so well received that I thought I would share it. To begin the project I created the circuit virtually. By starting this way I was able to work a lot of the kinks out of my design while also making sure to use only the parts that I had in my kit.

Step 1: Gather Your Parts

Picture of Gather Your Parts

Parts List:
1. 555
2. 7408 AND gate
3. 7447 BCD to decimal decoder
4. 74LS90 Decade counter
5. 74LS93 Counter
6. 74LS76 JK flip flop
7. 331 resistor chip
8. 104 capacitor, 1µf cap, and a 10µf cap
9. (2) 503 potentiometers
10. 10K potentiometer
11. (6)or (3 dual) seven segment displays (common anode)

Step 2: Minutes and Seconds

Picture of Minutes and Seconds

 I began with a 555 timer set up with three potentiometers, two are for the actual timing of the circuit and the third is in parallel with the 503 to allow the time to be set. The seconds and the minute’s portion of the circuit are identical so wiring these were straight forward. The 1’s of seconds receives the clock signal at the 74LS90 (Decade counter) it counts 0-9 then clocks a 74LS93 for the 10’s of seconds. The 93 is set to count 0-5 by running two of the outputs B and C through a 7408 AND gate which resets the IC on the sixth clock pulse and triggers the 74LS90 in the minute’s section of the circuit.

Step 3: Hours

Picture of Hours

The hours portion of the circuit while using the same components as both the seconds and the minutes is a little more challenging (Logically anyway). The first hours digit needs to count 1-9 then 0-2. This can be accomplished by tying pins 3, 6, and 7 to the output of the AND gate. By doing this it allows for a normal count 1-9 but when the second hours digit is a 1 these two high signals along with the B output on the 90 trigger the reset and clock starts over at 1:00.

Step 4: Run It

Picture of Run It

You can now impress all your friends with this very large and time comsummig project just like I have


Mesopexia (author)2016-06-28

Hello! I find this project really interesting, and I would like to build it too. Can you please send a clear schematic of the device to my e-mail? My e-mail is : -Thanks!

vrajeev (author)2016-02-04

Its a really cool project

i want to make one too...great job

vrajeev (author)2016-02-04

Please send me a copy of your circuit diagram with the complete parts list.

Genesisovi (author)2015-12-01

Please send me a copy of your circuit diagram with the complete parts list.

GustavoR25 (author)2015-11-25

Hi my friend can you please send me the schematics??

christanto (author)2015-01-21 . My email sir

christanto (author)2015-01-21

Sir please can you give me the schematics for my final task school sir.. pleasee..

stephen benedictP (author)2014-11-13

sir is that a home-made trainer.....and please make the pic. clear so that i can see the PICS. clearly....thank you???

takis.yannoulatos (author)2014-11-12

can you please send me the schematics??

cdurfey (author)2014-10-22

Please send me a copy of your circuit diagram with the complete parts list. I would like to make this with my son. Thanks

LiQ (author)2014-10-10

please send me a copy of your circuit diagram !! help me !!

gmail :

thank you very much

vincent.gonzales.984 (author)2014-07-31

please send me a copy of your circuit diagram !!

help me !!

yahoomail ::

jnimes (author)2014-02-24

the list of materials is not complete...

what diode did you use?

what value of resistor if I can't buy anywhere the 331 resistor chip?

what is 503 and 205 in the picture? is 503 really a potentiometer but it looks like a ceramic resistor?

also, in the schematic you provided there is the 3 input and gate which is 74ls11 if i'm not mistaken but you didn't include it in the list...

the schem you provided is blurred, can't read the labels of each component clearly....

i hope you would reply immediately ^^ i have read other comments saying it is working and I want to make it to but there are some missing information in your post. Thanks in advance :D

rezacumi (author)2013-12-05

does it can set the clock time?

imsajid (author)2013-04-15

Sir please send me the clear circuit. I have to submit my project report ..... please Sir My Email id is:

ughani2 (author)2012-12-12

plz send me circuit diagram for 12 Hour TTL clock
my email

darthneo (author)2011-11-11

Wow this is very impressive!

Can i ask how accurate your clock is with the 555 timer?

josgrg (author)darthneo2012-10-20

It is not as accurate as a real clock it loses appox. .68 sec a day which doesn't sound like much but over a large period of time say a week or a month the lose is significant.

waddaphak (author)2012-02-19

good day sir! can i have a copy of your pdf without having PRO ACCOUNT please.. ill be using it as a references in our on going project.. thanks

josgrg (author)waddaphak2012-10-20

I no longer have a copy of it. But if you do a internet search for a diagram you should find one easily.Sorry

Orion1615 (author)2012-10-19

I was wondering if you could use these parts to make a simple 30 second counter that would activate something or bleep when it comes to 0, with one button to reset it while its counting...

Its for a tiny little project so the simpler the circuit, the better, and this seems like a whole lot more advanced circuit... Any ideas?


josgrg (author)Orion16152012-10-20

Yes, it is possible but it is not very efficient or accurate. Because the 555 is used for a 1 Hz square wave the "timing " is not as stable as it needs to be for an actual timer.I would use a RTC ( real time clock) IC for the circuit you want it would make eveything much simpler.

trialex (author)2011-10-04

Wow excellent work!

I've been mucking around with a design using TTL chips like the very useful 4026 which combines a decade counter and 7-seg decoder into one chip. Of course nothing is simple, and I think I need a transistor driver between the 4026 and the LEDs, thereby negating the "all-in-one" advantage of the 4026.

How much current does your clock draw?

chochinooo (author)2011-09-25

this was awesome..thanks much but what was the led for??..

josgrg (author)chochinooo2011-09-26

The LED indicates A.M. or P.M.

iwoodinspire (author)2011-08-25

I did a counter on a giant breadboard similar to this in a digital electronics class too. Fun fun.

About This Instructable




Bio: I really like tearing things apart to discover how they work. I can even put them back together (most of the time). I have an ... More »
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