How to make a digital clock from discreet logic

How to make a [DIY]digital clock from discrete logic

This is going to be one of your favorite project when u complete it! Because you will learn so many things which u can use in your other projects and its completely going to be made from scratch therefore there will be no programming or micro controller whatsoever.

Check this video for overview of this project

                            

There are N number of ways of doing this project, but will take the most difficult path where we can learn a lot about electronics and I will share some of the tricks and tips to help do this project. Before we start let’s assume you know some basic knowledge of digital electronics.

If you want to learn all the topic in detail check the links given below

Clock signal: https://www.youtube.com/watch?v=AB2iVn8aZaE&t=38s

De-bouncing: https://www.allaboutcircuits.com/technical-articles/switch-bounce-how-to-deal-with-it/

Counter: https://circuitdigest.com/tutorial/synchronous-counter

We'll start with the display, It’s a seven segment display(SSD), made of 7 leds. In some case all the negative terminal of the led is connected to ground, this type of display is called common cathode and when all the positive terminals are connected to powersupply this is called common anonde. (COM in the picture refers to the common point)

7 segment display

we’ll pick a perfboard with 53x35 holes (I use perfboard instead of printed circuit board because by using pcb it still partially look like a DIY kit and by using perfboard beginners can learn to debug there circuit and fix it!)

with a space of 3 holes vertically and 2 holes horizontally place the first 7 segment display and with interval of 2 holes horizontally place the second display, these two combined show hours and then with interval of 7 holes horizontally place the display for minutes and seconds like we did for hours.

The first tip! Make the soldering understandable so as soon as u see the circuit u get what’s going on, and try to use minimum wire for jumpers which makes it look less clumsier. For this will spread out the 7 segment display leds in order from a to g and will solder as in the image and will do the same for all the 6 SSD (I have used many 100ohms resistors and connected them to the pin on the SSD from a to g, which is not necessary  it’s just to make the circuit look more complex you can instead replace a 470ohm resistor and connect it between ground and COM of SSD)

Second tip! If you soldered SSD upside down and you try to remove them and fix it your more like to make a mess which I did and with one of the SSD. But I found a way around to fix the problem without removing the SSD! Just add a jumper from the a to pin 7 and g to pin 10 of IC4026 which I have done with the green wire. By this the circuit will still work perfect like before! Except the decimal point move to top.

Now it’s time to make counter circuit, will start will only one SSD. The circuit is fairly simple 1IC for each display. You can see the circuit diagram from below, pin 10,12,13,9,11,6 and 7 are connected to pin a,b,c,d,e,f,g  of the display respectively and the switch which act as a mono pulse does not included in the final circuit because it will be replaced by a 555ic clock pulse generator circuit. You can directly install the IC in the board but in case of any issue it will be very hard to fix so I used a 16 IC socket so that I can easily mount and unmout the IC.

Will repeat the same for the other 5 SSD, for the solder layout see the image which shows how they are connected.

Pin 2 and pin 4 is connected to ground and pin 3 is connected to +12V then pin 5 of each of the IC is connected to pin 1 on the adjacent IC in order from seconds to hours.