Introduction: 24 Hr Digital Clock Only With Basic CMOS Chips

Picture of 24 Hr Digital Clock Only With Basic CMOS Chips

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 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

Picture of 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 are included in the block diagram

Step 2: PCB Layout & Explanation

Picture of PCB Layout & Explanation

The PCB is a 5x8 copper clad. Refer to the images below to understand the layout of the board. The red lines represent jumper wires. The next step will include the PCB art for the actual etching.

Caution: The 4543 BCD to decimal decoders are placed upside compared to all the other chips

Step 3: PCB Art

Picture of PCB Art

The actual PCB art for etching. It should come out as 5x8. I always like to place actual ICs on the paper to make sure everything lines up incase the page setup size needs to be increased or decreased slightly.

Etching the board:

1) Lightly sand the copper clad board. This seems to make the pattern stick better.
2) Set your laser printer on max toner density
3) Print out the PCB art on magazine paper. It may jam a few times, but it gives great results.
4) Iron the PCB art onto the board at your iron's maximum temperature. Apply alot of pressure for 15 minutes.
5) Soak in water to dissolve paper. Remove any excess paper.
6) Fix any broken traces with a sharpee.
7) Etch in ferric chloride which you can get at Radio Shack.

Step 4: Drilling Holes & Example Images

Picture of Drilling Holes & Example Images

I drilled my holes with a testors hobby hand drill. It worked out pretty well, except for a few poorly drilled places where I wasnt paying much attention.

Step 5: Populate the Board

Picture of Populate the Board

Populate the board with components. Be careful with the 4513s as they are upside down in orientation compared to the other chips on the board. Also, the crystal oscillator is a SOIC chip. I got mine on by pre-soldering the pads and having the chip melt into the pads. I am not sure if this is the best approach, but Iv never dealt with SOIC chips before.


k1200s made it! (author)2016-01-25

I made it!

AhmedO21 (author)k1200s2017-04-11

I'm trying to do this circuit but it doesn't work
Would send me your full circuit digram or a simulation for the circuit to be able to do it
Thank you very much

Roelymole (author)2016-03-21

It looks great but couldn't you just use a 4026 IC to drive the 7-segment display and as the decade counter. It could cut out up to 6 IC's.

BoraY2 (author)Roelymole2017-03-20

Resetting minutes to 00 after 59, or resetting hours to 00 after 23:59 would be a problem that way

BoraY2 (author)2017-02-13

4543 drivers has internal current limiting, no need for resistors.

Ed Marjosef (author)2017-02-05

Are the capacitors electrolytic or ceramic?... and what are the voltage of the capacitors?

flamesier (author)2015-05-28

anybody knows how to add milliseconds on this/.?

BoraY2 (author)flamesier2017-01-31

Forgot to mention, the display (and your eyes) will not be fast enough to see miliseconds displayed.

BoraY2 (author)flamesier2017-01-31

You need to copy the "seconds" portion as the miliseconds. Then cancel the AND gate for 59 to 00, and use a different clock signal (100 Hz) as this one uses 1 Hz.

AreeqA (author)2016-04-02

how the drop down resistors for each 7 segment display will be implemented ?
will each resistor be implemented at the output and input of the 4543 ?

SkyFireEX (author)AreeqA2016-04-03

Each resistor will be placed at the every output of the 4543 IC, connecting with its respective input at the 7-segment display. Use a 500Ω resistor for a bright display, or a 1000Ω resistor for a dimmer display. Not using any resistor will burn the display.

NeemY1 (author)2016-03-07

Good Day, is there any alternative for 4543 BCD to decimal Coonverter and 4020 Divide by 16384 counter??? any suggestion?? for other IC??? please reply asap thanks or email me on

k1200s (author)2016-01-24

Made the circuit, works great! Can anyone please tell me how to avoid the push buttons mechanical chatter, so when they're depressed to set hour/minute, it will only increment 1 hour or 1 minute at a time? The problem is that for each button press, it is now incrementing more than 1 hour or minute...It's the only "problem" that I'm having. Thanks!

Mattosx (author)k1200s2016-01-24

A small cap, maybe 0.1 microfarads in parallel with the switch should do the trick, mostly. Can you post a picture of the completed clock? I'd love to see :)

k1200s (author)Mattosx2016-01-25

Thanks for your advice, but unfortunately the solution that you've kindly made don't seems to work. I've done a google search about that problem (how to avoid mechanical chatter or contact bounce) and I can't fix the problem with none of those I've tried. This picture is from the 1st clock that I've made, and the second one, that is not finished yet, has the same problem.
Thanks again!
Best wishes,

bobo1313 (author)2014-12-08

Hi, Can i use a normal 32.768 KHz Crystal Oscillator instead of the CMOS one ?

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?

ChauH1 (author)bobo13132016-01-04

Yeah. Of course you can. But you have to use also 4060 and JK or D FF to divide pulse to standard 1Hz for your circuit.

flamesier (author)2015-05-29

anyone know how to make the led blink to indicate the second?

ChauH1 (author)flamesier2016-01-04

You can use CLK pulse from pin 9 of 2nd 4020 IC, through 1 or 2 Transistor connected series with LED. That'll make LED blink as you want.

Yit HengT (author)2015-06-12

what is the diode code?

ChauH1 (author)Yit HengT2016-01-04

I think 1N4148 is fine for this circuit. Trust me.

ChauH1 (author)Yit HengT2016-01-04

I think 1N4148 is fine for this circuit. Trust me.

sibu8222 (author)2015-11-20

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.

Grimm6Jack (author)sibu82222015-11-25

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.

Mattosx (author)Grimm6Jack2015-11-28

Correct. There is no throughole equivalent for this part. I literally let the pins melt into the pads with the pads being pre-soldered.

ZainA20 (author)Mattosx2015-11-30

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

MuhammadY34 (author)ZainA202015-12-09

i want to know how to put the oscillator and the input could you please help me with this problem

MuhammadY34 (author)Grimm6Jack2015-12-11

and the input is it gonna be from oscilloscopeor just a 5v power supply

and i wanna know if i able to remove the oscillator and get the clock and the voltage from the oscilloscope?

ZainA20 (author)MuhammadY342015-12-09

which oscillator do you have ?

about supply you can put it on two black boxes on uper left corner look in pcb design uper box as positive and lower as negative

sibu8222 (author)Mattosx2015-11-30

Thank you for the response! I still have a couple questions.

1. How would I solder this to work with a breadboard? I am assuming just solder a couple wires on it and then hook it in? The Oscillator only hooks into the first 4020 correct? So would it matter which of the 4 "pins" I connect to the 4020, versus what I connect a capacitor across?

2. Is the block diagram accurate enough to wire up this project onto a breadboard?

Grimm6Jack (author)sibu82222015-12-09

In the diagram you have the pins which are out to the 4020 or you can check it here:

About putting it on the breadboard, yes, you can solder some tin into the pins and put some wires and then put them in the breadboard, but it can have some bad contacts so be careful when soldering them. The SMD pins are very small as well which makes it even more difficulty.

trialex (author)2012-10-08

Hey I finally finished mine!

I made a few changes:
- I used a 4060 to divide a 32.678 crystal down to 2Hz - Which was then divided by a 4024 to 1Hz
- Used both "sides" of the 390's to save three ICs
- Used some ex-military displays that I salvaged from an old work project. They had the binary to 7 seg portion built in.
- Used point to point wiring

Still need to sort out a case / way to display it and what power supply I want to use.

Anyways thanks again for your help, I don't ever think I would have got the 60/24 reset working.

Photo attached (I think)

MuhammadY34 (author)trialex2015-12-09

could you please send me your shematic and your simulation file

Mattosx (author)trialex2012-10-21

Cute design! You really kept the component count down with those embedded chips in the displays themselves. That really cuts down on a lot of wiring. great implementation.

I chose to only use one side of each 390 to reduce the trace complexity on my PCB. It made it more linear.

How goes the time keeping? I am happy after two months mine has kept excellent time

MuhammadY34 (author)2015-12-09

please i want to know how you connect the crystal to the pcb ?

and which program you use to make the pcb?

MøhàmMáðÎ (author)2015-11-28

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

Mattosx (author)MøhàmMáðÎ2015-11-28

I don't have a proteus schematic. I drew the thing as a picture in Adobe Illustrator.

MøhàmMáðÎ (author)Mattosx2015-11-29

kindly answer these questions i have to submit this project next week but confused on two points..

I have two Questions from you

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

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..

ZainA20 (author)2015-11-29

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

shreddder999. (author)2015-10-09

Aren't you supposed to use all chips from the same family?

Mattosx (author)shreddder999.2015-11-28

I mean, using 74HC family should be fine.

Grimm6Jack (author)2015-11-11

Can you(or anyone else) link me/show me what type of crystal oscilator you used please?

Mattosx (author)Grimm6Jack2015-11-28

I wrote the DigiKey part in the discription.

Yit HengT (author)2015-06-11

How to make it without the second ?

Yit HengT (author)2015-06-11

jesse.tao.7 (author)2015-04-14

Can anyone send a multisim schematic of this please?

Mattosx (author)jesse.tao.72015-04-25

I don't have that, sorry.

clint.c.dillard (author)2015-04-25

Can't seem to get the diagram version to work the lcd won't light up

About This Instructable




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