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Seven segment display also known as seven segment indicator ,is
an electronic device  that display
decimal numbers. It is used in many things; for example digital watches  , electronic meters ,and basic calculators.

The seven segment consists of seven LEDs( light emitting diode) arranged
in rectangular fashion. Each of the seven LEDs is called segment because when illuminated
the segment forms parts of numerical digit to be displayed. An additional 8th
LED is sometimes used within the same package thus allowing the indication of a
decimal point ,when two or more seven segment display are connected together to
display numbers greater than ten.

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The display common pin is
generally used to identify which type of seven segment display it is .As each LED
has two connecting pins, one called the Anode and the other called Cathode .the
difference between the Common Anode and the Common Cathode is the way of
connecting of the seven segments .

2.2 Counters

Counters are
specially designed synchronous sequential circuits. They are usually
constructed of a number of flip flops connected in cascade, and they are very widely
used for measuring frequency and time. Counters are also similar to shift registers and other combinational circuits.

Counters are also known as digital circuit or timers. They are examples
for flip flop applications ;and here is an  example of how counter works ;4-bit counter is consists of 4 stages of cascaded J-K flip-flops. This
is a binary counter, since the output is in binary system format, i.e., only
two digits are used to represent the count, i.e., ‘1’ and ‘0’.  With only
4 bits, it can only count up to ‘1111’, or decimal number 15.

The output of counters is based on the clock
pulse application it can be used to count the number of pulses. We have two types of counters; the first one is when the counter has
only one clock ip  given to all flip flops
it is a synchronous counter, otherwise if the counter op the flip flops is the
clock signal nearby one it is asynchronous counter.

(You should write few (two to three)

2.3 Types of Counters

2.3.1 Asynchronous counter

In a 2 bit asynchronous counter, the exterior clock is connected
to the clock of the first flip flop and it changes the state at a decreasing
edge of every clock pulse, however in the second flip flop it changes only when
it is activated by the decreasing edge of Q of the first flip flop. The circuit
diagram of the two-bit ripple counter includes four different states each one
is consisting with a count value. Likewise, a counter with n flip flops can have
2n states. The number of state in a counter is called as its mod number. Therefore,
a two-bit counter is a mod-4 counter.

2.3.2 synchronous counter

In the synchronous counter , the CLK i/ps of all the FFs are connected
together and are activated by the i/p pulses. So, all the FFs change states
instantaneously. The circuit diagram below is a three bit synchronous counter.
The inputs J and K of flip-flop0 are connected to HIGH. Flip-flop 1 has its J
&K i/ps connected to the o/p of flip-flop0 (FF0), and the inputs J & K
of flip-flop2 (FF2) are connected to the o/p of an AND gate that is fed by the
o/ps of flip-flop0 and flip-flop1. When the both the outputs of FF0 & FF1
are HIGH. The positive edge of the fourth CLK pulse will cause FF2 to alter its
state because of the AND gate.

In the end this is
some proptes for each one

Asynchronous
counters:
a. Are also known as ripple counters;
b. are very simple;
c. use the minimum possible hardware (logic gates); employ flip-flops connected
serially, with each one triggering (clocking) the next;

d. have an overall
count which ‘ripples’ through, meaning the overall operation
is relatively slow;
e. require virtually no design.

Synchronous counters:
a. use interconnected flip-flops, but all are clocked together by the system
clock;
b. use the outputs from the flip-flops, to determine the next states of the
following flip-flops (rather than simply clocking them);
c. require no settling time due to rippling (as all flip-flops are clocked
synchronously);
d. need designing, to determine how the present state of the circuit must be
used to determine the next state (i.e. count);

1.4  Application of Counters

2.
From the given list of various
components at the left hand side of the screen of Cedar logic simulator select
“Registers” option and add 4-Bit counting register on the work area of the
simulator.

3.
From the list select “Input and
output” option and add 4-Bit LED display on the work area of the simulator.

4.
Connect the four outputs of
register with the corresponding four inputs of the LED display.

5.
From the list select “Input and
output” option and add “Variable rate square wave clock” to the work area of
the simulator.

6.
Connect the clock with the ^-shaped
input pin of the register.

7.
From the list select “Input and
output” option and add “Ground” to the work area of the simulator.

8.
Connect “Ground” with the “L”
output pin of the register.

9.
From the list select “Input and
output” option and add “Power (VDD)” to the work area of the simulator.

10. Connect
“Power” with the “C” and “U” output pins of the register using a 4-way junction
from the “Invert and connect” option of the list.

a 2-input AND gate on the work area of the simulator.

12. If
you want to reset the display of LED to 0 after displaying the output 5, you should
connect the output pins of the register for digits 1 and 4 with the inputs of
AND gate using two 4-way junctions.

13. Connect
the output of the AND gate with the “Reset” input pin of the register.

14. The
entire circuit will look like the following:

15.
Design Steps

We want to design a counter  that counts from 0-59

So we will make two counters and one counts
from 0-9 and the other from 0-5 and d-flip flop .

0-5 counter

Step 1 :
select “Registers” option and add 4-Bit counting register on the work area of
the simulator.

Step2:
From the list select “Input and output” option and add 4-Bit LED display on the
work area of the simulator.

Step 3:
Connect the four outputs of register with the corresponding four inputs of the
LED display.

Step4:From the list select “flip flop” option and add
“D-flip flop” to the work area of the simulator.

Step5: Connect the  Q in the D-flip flop with the ^-shaped input
pin of the register.

Step6:From the list select “Input and output” option
and add “Ground” to the work area of the simulator.

Step7:Connect “Ground” with the “L” output pin of the
register.

Step8:From the list select “Input and output” option
and add “Power (VDD)” to the work area of the simulator.

Step9:Connect “Power” with the “C” and “U” output pins
of the register using a 4-way junction from the “Invert and connect” option of
the list.

Step10:Add a 2-input AND gate on the work area of the
simulator.

Step11:Connect the R input pin of the register to the
out put of the And gate

Step12:Connect the first input in the and gate with
the third output pin pf the register.

Step13:Connect the second input in the and gate with the
first output pin in the register.

0-9 counter

Step 1 :
select “Registers” option and add 4-Bit counting register on the work area of
the simulator.

Step2:
From the list select “Input and output” option and add 4-Bit LED display on the
work area of the simulator.

Step 3:
Connect the four outputs of register with the corresponding four inputs of the
LED display.

Step 4:
From the list select “Input and output” option and add “Variable rate square
wave clock” to the work area of the simulator.

Connect the clock with the ^-shaped input pin of the
register. 