Description and concept behind digital clock
This digital alarm clock project use 4026 IC which is decade counter as well as seven segment driver . Seven segment display is used for displaying number from 0 to 9 and it will display number when the enable pin of 4026 is high on the rising edge of clock ie the circuit start counting and displaying result when the enable pin is made high. Each seven segment display need very few current to glow LED inside it so we have to use 500-ohm resistor on each segment so that we would not be blown off the LED.
7806 is voltage regulator IC this part of the circuit is used to maintain power supply to the circuit but if you are using simulation tool like Proteus you will not need this circuit.
Another important thing to be noted is counting less than 9 can be achieved by connecting that pin to the reset. For example, to count from 0 to 5 6 should be connected to reset pin so that if the counter reaches to threshold ie 5 then it goes to reset in next counting step.
And the last thing to remember is this circuit uses external clock source of 1 Hz frequency. If you want to make your own clock please refer this diagram of 555 timer ic. This will produce exact of 1 Hz clock. if this is not 1 Hz frequency please maintain it by changing variable resistor or capacitor.