Hook
Ever wondered how a digital clock work without
complex mechanism unlike analogue clock.
In this video will look on how to make this
super complex digital clock without any DIY
kit or microcontroller. Will just use some
fairly basic logical circuits.
This is going to be a beginner/intermediate
tutorial so basic knowledge of electronics
is enough to watch this tutorial.
Without any further delay let’s get started.
So how does the digital clock work?
First will call digital clock as Timekeeper
to avoid confuse between the term clock in
electronics.
Working of timekeeper is way easier than u
thought of how it may work. It’s just a
counter which count clock pulse!
So u came cross 2 term clock and counter!
Clock: is a particular type of signal that
oscillates between on and off state of a circuit
at certain frequency, more likely a metronome.
Mathematically we know time is equal to inverse
of frequency, If we can generate a clock pulse
of one hertz, we can turn on and off the switch
with time interval of one second.
Counter: is a digital circuit which is usually
constructed many flip flop which is used to
The good news is we already have few IC for
these circuit so we don’t have to build
detail about the clock and counter…
If u want to learn more about these circuit
the click the I icon or link in the description
What we learned so far…
A digital timekeeper(clock) is just a circuit
that count the number of clock signal and
it uses some logic to format the time that
we see. enough of talking let’s just get
right into the fun part!
We’ll start with a display!!
I used an old-school like display called 7
segment display also known as SSD.
There are 2 types of 7 segment displays
• Common anode
• Common cathode
In this video We’ll use common cathode.
In this display all the negative terminals
are tied to a common point therefore we can
display alphanumerical value by changing the
state of pins which are named from a to g.
We need 6 of these in total. 2 for seconds,
2 for minutes and 2 for hours
There are so many different IC and methods
to work with this display.
But I will stick on to ic4026 because I just
need one of them for each of the display.
If u want to learn more about these circuit
comment below. It will be a topic for upcoming
videos.
If we see the data sheet of 4026. It gives
what each of the pin exactly do. and if we
move further we get the operation condition
which is quite useful (so we don’t blow
up the circuit like a noob).
First let’s put this on a circuit diagram.
I just connected all the pins from a to g
on the ic4026 to the respective pins on the
SSD and I built the rest of the circuit with
reference to the datasheet. After I implemented
the circuit in a bread board and added a simple
switch which act as a manual clock pulse for
the ic.
U can see the circuit start counting!!!
now we can automate the click. To do this,
there are several ways but will use 555ic
to generate a signal of one hertz because
the circuit is simple and as I’m very lazy.
But you are free to find out other methods
on internet which is more accurate and complex.
As this circuit is simple and most of them
familiar with it. we will just start building
the circuit on the bread board. For more detailed
explanation and other information check out
the link in the description or the link will
be given at the end of the video.
After completing I just removed the switch
and connected the pin 3 of 555 IC to the pin
1 on the IC 4026.
And here we go!!!
We got the output as expected! As I have added
a variable resistor in the final circuit we
can adjust the frequency of the clock pulse
to 1 hertz more precisely using an oscilloscope…
just connect the pin 3 to positive of oscilloscope
and ground to ground of oscilloscope. Then
by change the value of resistor we can adjust
the frequency to 1hz.
Next step is just to cascade them and format
the time as we need!
Now we need to build 6 similar 4026 circuit
without the clock input. and once done connect
the pin 5 of 6th 4026ic to pin 1 of 5th 4026ic
and pin 5 of 4th 4026ic to pin 1 of 4th 4026ic,
pin 5 of 2nd 4026ic to pin 1 of 1st 4026ic.
(I know many couldn’t get that, but If u
did your genius! For those don’t, Just Check
the link which explain all these in detail)
What we actually did is, we just cascaded
the display individually so each of 2 of six
SSD can count up to 99 individually….
Now we need a logic which can control the
flow and trigger the minute when the seconds
reach 60 and trigger the hours when the minute
reaches 60.
First we are going to check whether the tens
place of seconds display reach 6. Keep an
eye on the 3 leds they are lit only when the
digit 6 appears. So here we go!! We got a
hint. now we should just reset seconds and
increment the minute when all this 3 leds
are lit…
This is applicable only for minutes and seconds.
For hours look at this 3 leds they are lit
when the digit is 24…u can also use the
same concept and make It for 12 …
To implement this logic in our circuit will
use a IC 7411 which have triple 3 input AND
gates. The output of the gate is high only
if all the inputs of the gate is high. Or
in other words when all the 3 leds are lit
they are going to output an on state.
So now we just need few buttons to set the
time manually so we can use them in a more
practical way. So will add the switch to the
minute and hour before that I added a couple
of diode which controls the back flow and
allows current to flow through only one direction…so
it won’t affect the seconds when minute
is changed and same goes for the hours. The
switches are connected to pin 1 of the minute
and the hours IC.
There is one problem. That’s, bouncing of
the circuit!
Bouncing is the tendency of ant two metal
contacts in an electronic device to generate
multiple signals as the contacts close or
open;
De-bouncing is any king of hardware or software
that ensures that only a single signal will
be acted upon for a single opening or closing
of a contact.
The circuit is fairly simple than the definition,
it’s just made of a resistor and a capacitor.
Will just replace the switch with this circuit.
If you see my circuit you can see an extra
additional IC (7414) which I used for de-bouncing
circuit… Actually it was over kill.. I Faced
many issues when I used this circuit and I
used many resistor and diode to solve the
problem So I prefer using the easier one.
So are we done?
There is one thing missing! The power supply.
Will use a 12 volt 1A power brick. So we have
to do some minor changes to the circuit. Will
place a small socket then connecting it to
the power supply line and ground. Now we are
done with the circuit!
It’s time for the case!
Will grab some sheet of paper a draw a reference
layout for the case. The values of the measurement
may vary from yours, depending on your circuit
size. Now will you this as a reference and
cut this out from an acrylic sheet. Once we
have the sheet will draw a square of 1.5cm
and will mark the midpoint to the diagonal
and drill with a 3mm drill bit and increase
the size with a 5mm drill bit. Then will cut
some small pieces acrylic for holding the
circuit. Then will use some acrylic glue and
paste the small pieces. Once done we can fasten
the case with few nuts and bolts.
You can see the case is designed such that
we can access the hours…. And as well as
minutes , and also access both the frequency
of the clock and power socket without taking
it of the case….
There are so many effective ways of doing
it… u can improve so many things in the
circuit …like changing the clock circuit,
by changing the SSD driver circuit, by changing
the de-bouncing circuit etc… With proper
tools you can fix the issues I had in making
the case like I couldn’t have perfect cut….and
I made couple of scratches which you can avoid.
And importantly… the clock will reset after
the power is removed.
The cost of building this circuit may be slightly
high compared to a DIY kit… But you can
learn a lot and you will have very good solder
practice.
You can drop your questions and doubts in
the comment section…
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By clicking the link on the screen u can check
out other videos.
As always see you guys later.
