PCB art is included in this instructable so you can easily make it!

A 24 hour based clock based on dual decade counters, AND gates, OR gates, BCD to Decimal Converters, and a crystal oscillator. No micro controllers here. This instructable contains PCB art so you can easily make your own.

Quantity is in parentheses. Item number at Digikey.com is in brackets.

(6) 74HC390 Dual Decade Counters [568-1442-5-ND]
(6) 4543 BCD to Decimal Converters [568-3138-5-ND]
(2) 4020 Divide by 16384 Counter [296-2039-5-ND]
(1) 74HC32 Quad OR Gate [568-1434-5-ND]
(1) 74HC08 Quad AND Gate [TC74HC08APF-ND]
(39) 500Ω or 1000Ω drop down resistors for 7 segment displays
(3) 10kΩ Resistors
(6) Common Anode 7-Segment Displays [160-1575-5-ND]
(4) 3 mm Green LEDs
(1) 100 uF Capacitor
(1) 0.1 uF Capacitor across Crystal Oscillator
(1) CMOS 32.768 KHz Crystal Oscillator [SER3618CT-ND]
(3) Momentary Switches [P8071SCT-ND]
(4) 3 mm Green LEDs
(1) Power Plug [CP-102A-ND]
(1) 5V Power Supply

Step 1: The gist of how it works

A 32,768 Hz oscillator provides the clock pulse and this is divided by two CMOS 4020 Divider chips down to 1 Hz. The 1 Hz signal is fed into the first dual decade counter [IC3] that runs from 0-9. The binary coded decimal from IC3 is fed into a 4543 [IC4] that is converted for a seven segment display. The block diagram omits showing the drop down resistors, but they're really there. Use either 500Ω for a bright display or 1000Ω for a dimmer display.

IC3 triggers IC5 by feeding its IC3's q3 output into IC5's clock input. IC5 runs from 0-5 and resets via an AND gate when it hits 6. The AND gate also feeds into IC7 which is the minutes section. IC9 resets at 6 as well. This completes the minutes section. 

The AND gate from the minute section increments the hour section. Another AND gate in the hours section resets IC11 and IC13 simultaneously when  they collectively reach 24. 

This probably sounded all convoluted, dense, and confusing. Refer to the diagrams below for more clarity.

Notice part numbers from DIgikey.com are included in the block diagram
<p>So I ordered the CMOS 32.768 KHz Crystal Oscillator, how do I wire this thing up? There are no pins on it and it is very small. </p>
<p>No wire... That's an SMD CMOS Crystal Oschillator, you just put it into the squares(look at PCB art). Before, you melt down some tin on it.</p>
<p>Correct. There is no throughole equivalent for this part. I literally let the pins melt into the pads with the pads being pre-soldered.</p>
<p>please any one can help me placing the oscillator. oscillator used in this have four pins out but i got from market the crystal oscillator with two pins out just looks like capacitor but how do i place it instead of that four pin oscillator ? anyone help plz</p>
<p>i need proteus schemetic of this circuit becaus i can not understand jumpers used in this project without that orignal Schemetic of this circuit made on that specific software used for PCB layout.. kindly provide me that one schemetic of this circuit on m.ibrar.1996@ieee.org</p>
<p>I don't have a proteus schematic. I drew the thing as a picture in Adobe Illustrator.</p>
<p>kindly answer these questions i have to submit this project next week but confused on two points..</p><p>I have two Questions from you</p><p>1) i don't understand from where input will be given on pcb ?? there is no input connector on Your design tell about input connection location on PCB lay out</p><p>2)In final picture of your project where is Oscillator located ? i mean in schemetic oscillator is before 4020 counter but in PCB lay out and final project picture oscillator is not soldered in that position..</p>
<p>please any one can help me placing the oscillator. oscillator used in this have four pins out but i got from market the crystal oscillator with two pins out just looks like capacitor but how do i place it instead of that four pin oscillator ? anyone help plz</p>
<p>Aren't you supposed to use all chips from the same family?</p>
<p>I mean, using 74HC family should be fine.</p>
<p>Can you(or anyone else) link me/show me what type of crystal oscilator you used please?</p>
<p>I wrote the DigiKey part in the discription.</p>
<p>very good!! :)</p>
<p>wowow very good</p>
<p>what is the diode code?</p>
<p>How to make it without the second ?</p>
<p>anyone know how to make the led blink to indicate the second?</p>
<p>anybody knows how to add milliseconds on this/.?</p>
<p>Can anyone send a multisim schematic of this please?</p><p>houseestateaq@gmail.com</p>
<p>I don't have that, sorry.</p>
Can't seem to get the diagram version to work the lcd won't light up
Didn't you use the PCB art? Is it getting power?
<p>can anyone send me the schematic of this digital clock..plz..</p><p>johnny_farjo@live.com</p>
<p>Switches don't work on Proteus, any body else?</p>
<p>Hi, Can i use a normal 32.768 KHz Crystal Oscillator instead of the CMOS one ?</p><p>i mean i want to buy and use a normal Crystal Oscillator NOT the CMOS Crystal Oscillator,and what would be the part number on digikey?</p>
<p>Hi, I just want to ask if what is the purpose of the momentary switch you have? And if the circuit has an on-off switch? If yes, will the time still be accurate after it was turned off and then turned on again?</p>
<p>Where should I connect the 5volt input? Thank you.</p>
<p>how to add rtc module, its be?</p>
<p>Roughly how much did this build cost altogother?</p>
<p>It depends. If you already have the base equipment then the materials only is maybe $25</p>
Hello, I am very keen on making this but i am a novice and are affraid of messing it up badly. i am also wondering, will it keep time for a long time or should i expect to lose time? tfeedback would be much appreciated (:
<p>You could always just build it on a breadboard so you don't have to solder anything. It wont be as pretty but until you get it right would be the easiest way. </p>
<p>I have had mine running now for nearly two years and it keeps time great. Maybe a few seconds every several months is lost if it all.</p><p>My advice is that if you take your time and make sure you do it &quot;cleanly&quot; it should work, that is, nice solder connections and everything is tidy. We could always trouble shoot if here because I know the circuit so well.</p>
Hello.. Is this a countdown clock display?
<p>No, it counts up as a 24 hour clock.</p>
<p>Where can you submit designed PCB's and get them printed?</p><p>And what kind of voltage source are you using? Wall outlet into a transformer or batteries?</p>
<p>The voltage supply is around 5V. A lot of old cell phone chargers work great because they're around 5-6V and the circuit works with fairly small current.</p><p>And for circuits boards, I never found a good place to get just one or a few printed economically. This board is 40 square inches (8x5) and some places $3-$4 per square inch! So I make my own.</p>
clock has been keeping perfect time for about for about 4 month now.. but recently has been resetting the hours every 20 minutes..in other words the minutes are only counting to 19 instead of 60 as before. Any clue as to what could be happening?
Yes, I know why. The 74HC390 decade counter has outputs Q0, Q1, Q2, and Q3 outputs a six when Q1 and Q2 go high which feeds into the AND gate. Likely there is a poor electrical connection between Q2 and the AND gate. This is occurring on the IC in the middle row, third from the left. <br>
Thank you very much for sharing this great project. I had to give it a try and had a blast. very inspiring. Here's the one I made. http://www.instructables.com/files/deriv/FZF/6VD8/HJ5ZVU76/FZF6VD8HJ5ZVU76.MEDIUM.jpg
can any one tell me if I want to add the alarm in this clock then what will be its logic and how can i do that??????&quot;plzzzz zzzz&quot;
make a clock
Excellent work! <br> <br>Do you know what the average current draw is?
Yes, I seem to recall it's hovering around 150 mA. One of the nice thing about this clock is that when the power goes out which it did during a thunder storm two days ago, it keeps the time. The logic seems to run off the 100 uF smoothing cap for a while. The ICs appear to use next to nothing for current.
Cool, thanks for the reply. That current draw is way less than I was expecting.<br> <br> Having never been formally taught electronics logic, I've been trying to teach myself a bit, and a CMOS/TTL clock is what I'm hoping to achieve next. I think my biggest stumbling block has been the 60sec/60minute reset, so I'm studying your layout. Can't say I understand it yet, so standby for more questions :-)<br> <br> I've been planning on using 4026's (<a href="http://www.ti.com/lit/ds/symlink/cd4026b.pdf" rel="nofollow">http://www.ti.com/lit/ds/symlink/cd4026b.pdf</a>) for my clock - they seem to be a combination of the 390's and 4543's (as in decade counter + 7 seg driver) you use. I'm still comparing datasheets, but can you comment on any advantage/disadvantage of the two options? Seems like using 4026's would save one chip per digit - note that this may not be a good thing if you are going for geek cred :-). The 4026's do have a very small output current limit which might mean transistors are needed before the LEDs, which means you lose the advantage of a smaller part count.<br> <br> Thanks again
You would have a boatload of transistors if you use the 4026. You need a transistor for each segment and 6x7 = 42 transistors = 126 PCB holes for the transistors. The six 4543s would have 6x16 = 96 PCB holes. And I bet the transistors used as switches would consume more current. <br> <br>Regarding the logic, the decade counter does what it says, it counts from 0-9. Such a decade counter handles the right digit of something like 59. Now we want the left hand digit to only go up to 5 obviously. So when the left digit hits six, or 0110, we feed the 11 of 0110 into an AND gate and the AND resets the 6 back to 0. It happens so amazingly fast that you never see the 6 on the display.
According to this website it says many different 7 - segment displays can be powered from the 4026 when operating it on 9V. We used this IC at school and we powered 7 - segment displays from it just fine. To me it seems a little at that a 7 - segment display counter IC would exist if it wasn't suitable for connecting it straight to an output?
I think I was trying to take the reset signal off the lines between the BCD-&gt;7seg chip and the display, rather than straight after the decade counter. I couldn't get these to reliably trigger an AND gate, so reset never happened. I have no idea why I didn't try it at the decade counter output, when I saw yours it was an aha! moment. <br> <br>Looking more at the 74HC390 chip, it's a DUAL decade ripple counter, with totally separate inputs, outputs and resets. It seems like you could use a single 390 to drive two 7seg displays (i.e. seconds and 10's of seconds using the same chip). Any thoughts on this? (Still waiting for my 390's to arrive to test it myself).

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