Thursday, December 30, 2010

Digital Clock based on 74ls90

Digital clock never get obsolete on digital electronic projects.

Many approach and design are available online but implementing it using 7490 decade counter is one of the easiest design. This can be proven by looking at its simplicity and compactness.

Check its datasheet to see it's pin configuration and how it's being implemented.

On our digital clock circuit. We will use divide-by 10, divide-by 6 and divide-by 2. This circuit design is not adjustable so you need to start the clock exactly 00:00 or 12am.

here's the circuit of 7490 to be used:

for SECONDS' ones, MINUTES' ones and HOURS' ones are divide by 10.

for SECONDS' tens and MINUTES' tens are divide by 6.

for HOURS' ones is divide by 2.

please refer to the diagram below for the appropriate circuit.

The output of the HOURS' tens digit is connected to an AND gate that will reset the counter to 00 when 12 is counted.

The clock source will depend on the designer. It can be a 60hz from the powerline, 555 astable mode, crystal oscillator or any oscillators.

here's the circuit:

Here's the simulation video using Proteus Isis 7 (Download proteus here):


Anonymous said...

the circuit is working but the problem is every time i run the circuit, the seconds starts at 44.

Circuit Desolator said...

I am wondering why your seconds hand starts at 44. As expected, it should start at 00. Kindly check the wiring and update us on your progress.

Anonymous said...

I seem to understand what is going on. Any suggestions on how to count to 24 for the hours... i.e. a 24 hour clock?

Anonymous said...

Two questions for the hours, what mods are your counters? And any suggestions on how to do a 24 hour clock... so changing the hour part from counting to 12 to counting to 24 :)

Anonymous said...

Two questions, for your hours, what mods are your counters? And do you have any suggestions on how to do a 24 hour clock? so changing to hours from counting to 11 and restarting to counting to 23 and restarting.

indran said...

How do you reset clock.Reset the HR & Mins

Anonymous said...

how do reset the time.there are no buttons to reset

Anonymous said...

Sir i am currently building the hardware of this and has the ares layout(yes. w/n this week it is now on PCB) and isis simulation. can you pls add a button to manually set the sec,min and hr? thanks.