Make A Digital Clock From Scratch

Step 2 The Seven Segment Display

The clock is made of six seven segment displays which make up the display.
Each digit made of seven segments and every segment made of 3 LEDs in parallel.
So a simple calculation gives that there are 21 LEDs in each seven segment display.
And all six digits take 126 LEDs.
But as I said In the parts list you will need 130 LEDs and the other 4 LEDs are going to be used as dots that separate the hours, minutes and the seconds.
I made a common cathode display which means the all the negatives leads are connected together.

Now you will need to choose the right resistor for current limiting to 3 LEDs in parallel.
The calculation is simple and gos like this : 
R=(Vcc-Vled)/(Iled*3)
R= the resistor value
Vcc = The voltage that is supplied
Vled = the forward voltage on the LED
Iled =the current the LED takes

You should always take a value a little bit bigger then the one in your calculation just to be on the safe side.
 

Comments

[glado]

hi im new here i really like your project and i was study yours diagrams but the displays connection to drivers are unclear for me ..i understand that the segments are connected together as one digit and they drive by transistors this is clear,, but i can understand connection of (4017) transistors to displays ..could you post any diagrams of good connection drivers and displays please ? this will be helpful to understand your project i love way of using arduino and programing it makes this project so simple thanks for sharing you knowledge! if you can email me via my account that would be great thanks a lot !!

[robot797]

the displays are common cathode that means all the - wires come to one point inside the display the counter cycles between every display to get a stable and image to the human eye

[Syst3mX]

The idea is that every every transistor that is connected to the 4017 has a "free" collector pin. You need to connect this pin to the negative connection on the segments(in each segment you have a common negative rail).
So the first transistor is connected to the first segment ,and the second transistor is connected to the second segment and so on.

I will make a new digram on the weekend but until then I hope my explanation helped.

[adil.ali2010]

Could you please send me the PDF file. I want to make it.
my email is [e-mail]

[glado]

thanks a lot ....could you check diagram placed below ? i would like to know if i understood you correctly ....is this work like on this diagram ? or in some different way thanks again thanks for help im just starting with electronics .....

[Syst3mX]

Yep thats right