Digital clock notes

*** Explain the construction, working of Digital clock

·           A 60Hz time base power line is needed to operate Digital Clock.

·           A bridge rectifier is used to convert A.C to D.C

·           7805 IC voltage regulator is used for a constant voltage.

·           A least four 7490 counters, two 7447 binary to 7-segment converters are used for construction.

·           330Ω  resisters 20, some normal LED’s, two common-anode 7-segment LED displays are wanted  to design a Digital Clock.

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Construction:-

·           A decade counter  (7490) is used to count from 0 to 9 in a natural mode as a cyclic.

·           We get the 4-bit binary number in Q_A ,Q_B,Q_C and Q_D  pins as output.

·           Up mode counting process is going on it, after getting the maximum count (number) then returns to zero.

·           We “set it Up” by writing the R0₁,R0₂ ,R9₁ and R9₂  lines.

·           If both R0₁  and R0₂  are connected to 5V or logic1 and either  R9_{1  ,}  R9₂   are connected to ground (logic 0)

·           Then counter will reset. i.e Q_A ,Q_B,Q_C and Q_D   become zero.

·           If both  R9₁ and R9₂  are connected to 5V (logic1), then the count on  Q_A ,Q_B,Q_C and Q_D goes to 1001.

 Working

To create a divide by 10- counter:

 ·           First connect pin 5 to  5V and pin-10 to ground.

·           Then connect pin-12 to pin-1 & pins 2,3,6,7 are    connected to ground.

·           Then run the input clock signal from the time base or a previous counter on pin 14.

·           The output appears on Q_A ,Q_B,Q_C and Q_D   .

·            The output of pin-11 is connected to the next stage.

To create a divide by 6- counter:

·           First connect pin-5 to 5V and pin-10 to ground.

·            Then connect pin-12 to pin-1 & pin-2 to pin-9 & pin-3 to pin-8.

·           Pin- 6 and pin-7 are connected to ground.

·           Run the input clock signal from the time base or a previous counter on pin-14.

·            The output appears on Q_A ,Q_B and  Q_C.

·            The output of Pin-8 is connected to next stage.

Creating the second Hand:

·           In this diagram the top two 7490’s divide the 60 Hz signal from the    power supply down by a factor of 60.

·           The 3^rd  7490 takes 1Hz signal as input and divide by 10.

·           Its 4  output’s drive normal LED’s in this diagram.

·           The 4^TH  7490 divides the output of the third by 6 and its three outputs drive normal LED’s as well.

Displaying the time as Numerals:

·           To display  the time as numerals we use the 7447 to connect 7490.

·           To power on the 7447 pin-16 is connect to 5V and pin-8 to ground.

·           Connect Q_A ,Q_B,Q_C and Q_D    from 7490 to pin-7,1,2, &6 of 7447.

·                 Connect 330Ω resistors to pins 13,12,11,10,9,15,14 of the   7447.

·           Connect resistors through a, b, c, d, e, f & g segments to the 7-segmentLED.

·            Connect the common anode of the 7-Segment LED to 5V.

To create the minute hand section:

·           We need duplicate “Second hand” portion to create the “Minute hand” section

·           To create the “Hour Hand” portion we want to use an AND gate or inputs of the 7490.

·           After recognizing the binary number 24 ,the hour counter reset to zero.

For a setting mechanism:-

·           For  setting the clock ( digital clock system ) just move the input wires to drive higher- frequency signals into the “minute-hand” section of the clock.

·           In a real clock we use push buttons (or) switches and gates to do the same operation (working).

·           In clocks (or) watches for the alarm & other features we (connected) including low-power chips.

·            The chip is probably embedded directly into the circuit board.