This document describes the design of a 0-9 binary coded decimal (BCD) counter circuit. It uses a 74LS90 BCD counter integrated circuit to generate the BCD codes from 0 to 9, and a 74LS47 7-segment display driver to decode and display the codes on a 7-segment display. The circuit was designed, breadboarded, and simulated in Digital Works to verify its functioning, counting from 0-9 each time a push button switch is pressed before resetting. Cascading multiple BCD counters can extend the counting range to larger numbers.

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Index
1. INTRODUCTION.
1.1 Objective of Project
2. LITERATURE SURVEY:
1.1 Existing System
3. DESIGN.
3.1 Module design and organization
3.2 Components and Requirements.
3.3 Explanation of Working System
3. IMPLEMENTATION & RESULTS.
4. Future scopes
5. Datasheets
6. CONCLUSION OF PROJECT.
7. References

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TITLE: 0-9 Binary Coded Digit Counter.
Introduction:
Objective: To design 0-9 BCD Counter Circuit
General State Diagram:
 Then a decade counter has four flip-flops and 16 potential states, of which only 10 are
used and if we connected a series of counters together we could counter to 100 or 1,000
or whatever number we wanted.
 The total number of counts that a counter can count too is called its MODULUS. A
counter that returns to zero after n counts is called a modulo-n counter, for example a
modulo-8 (MOD-8), or modulo-16 (MOD-16) counter, etc, and for an “n-bit counter”, the
full range of the count is from 0 to 2n-1.
 But as we saw in the Asynchronous Counters tutorial, that a counter which resets after ten
counts with a divide-by-10 count sequence from binary 0000 (decimal “0”) through
to 1001 (decimal “9”) is called a binary-coded-decimal counter or BCD Counter for short
and a MOD-10 counter can be constructed using a minimum of four toggle flip-flops.
 It is called a BCD counter because its ten-state sequence is that of a BCD code and does
not have a regular pattern, unlike a straight binary counter. Then a single stage BCD
counter such as the 74LS90 counts from decimal 0 to decimal 9 and is therefore capable
of counting up to a maximum of nine pulses. Note also that a digital counter may count
up or count down or count up and down (bidirectional) depending on an input control
signal.
 Binary-coded-decimal code is an 8421-code consisting of four binary digits. The 8421
designation refers to the binary weight of the four digits or bits used. For example, 23
= 8,
22
= 4, 21
= 2 and 20
= 1. The main advantage of BCD code is that it allows for the easy
conversion between decimal and binary forms of numbers.

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Existing Systems
Integrated Circuit 74LS90 BCD Counter
 The counters four outputs are designated by the letter symbol Q with a numeric subscript
equal to the binary weight of the corresponding bit in the BCD counter circuits code. So
for example, QA, QB, QC and QD. The 74LS90 counting sequence is triggered on the
negative going edge of the clock signal, that is when the clock signal CLK goes from
logic 1 (HIGH) to logic 0 (LOW).
 The additional input pins R1 and R2 are counter “reset” pins while inputs S1 and S2 are
“set” pins. When connected to logic 1, the Reset inputs R1 and R2 reset the counter back
to zero, 0 (0000), and when the Set inputs S1 and S2 are connected to logic 1, they Set
the counter to maximum, or 9 (1001) regardless of the actual count number or position.
 As we said before, the 74LS90 counter consists of a divide-by-2 counter and a divide-by-
5 counter within the same package. Then we can use either counter to produce a divide-
by-2 frequency counter only, a divide-by-5 frequency counter only or the two together to
produce our desired divide-by-10 BCD counter.

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Integrated Circuit 74LS90 BCD Decade Counter
 Successive applications of the push-button switch, SW1 will increase the count up to
nine, 1001. At the tenth application, the outputs ABCD will reset back to zero to start a
new count sequence. With such a MOD-10 round number of pulses we can use the
decade counter to drive a digital display.
 If we want to display the count sequence using a seven-segment display, the BCD output
needs to be decoded appropriately before it can be displayed. A digital circuit that can
decode the four outputs of our 74LS90 BCD counter and light up the required segments
of the display is called a Decoder.

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Integrated Circuit 74LS47 BCD to 7-segment Driver
 Fortunately for us, someone has already designed and developed a BCD to 7-segment
Display DecoderIC such as the 74LS47 to do just that. The 74LS47 has four inputs for
the BCD digits A, B, C and D and outputs for each of the segments of the seven-segment
display.
 Note that a standard 7-segment LED display generally has 8 input connections, one for
each LED segment and one that acts as a common terminal or connection for all the
internal display segments. Some displays also have a decimal point (DP) option.
 The 74LS47 display decoder receives the BCD code and generates the necessary signals
to activate the appropriate LED segments responsible for displaying the number of pulses
applied. As the 74LS47 decoder is designed for driving a common-anode display, a LOW
(logic-0) output will illuminate an LED segment while a HIGH (logic-1) output will turn
it “OFF”. For normal operation, the LT (Lamp test), BI/RBO (Blanking Input/Ripple
Blanking Output) and RBI (Ripple Blanking Input) must all be open or connected to
logic-1 (HIGH).
 Note that while the 74LS47 has active LOW outputs and is designed to decode a common
anode 7 segment LED display, the 74LS48 decoder/driver IC is exactly the same except
that it has active HIGH outputs designed to decode a common cathode 7 segment display.
So depending upon the type of 7-segment LED display you have you may need a 74LS47
or a 74LS48 decoder IC.
 The 74LS47 binary coded decimal inputs can be connected to the corresponding outputs
of the 74LS90 BCD Counter to display the count sequence on the 7-segment display as
shown each time the push button SW1 is pressed. By changing the position of the push
button and 10kΩ resistor, the count can be made to change on the activation or release of
the push button switch, SW1.

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Components Required and Datasheets of IC 74LS90 and IC 74LS47
7 - Segment Display

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Design Of 4 Bit 0-9 Decade Counter:
 Note that a 7-segment display is made of seven individual light emitting diodes to form
the display. The best method of limiting the current through a seven-segment display is to
use a current limiting resistor in series with each of the seven LED’s as shown. But we
can do this in two ways.
 Our circuit shows a simple 0 to 9 digital counters using a 74LS90 BCD Counter and a
74LS47 7-segment display driver. To count above 10 and produce a 2-digit base-ten
counter and display, we would need to cascade two separate divide-by-ten counters
together. A 2-digit BCD counter would count in decimal from 00 to 99 (0000 0000 to
1001 1001) and then reset back to 00. Note that although it will be a 2-digit counter,
values representing Hexadecimal numbers from A through F are not valid in this code.
 Likewise, if we wanted to count from 0 up to 999 (0000 0000 0000 to 1001 1001 1001),
then three cascaded decade counters are required. In fact, multiple decade counters can be
constructed simply by cascading together individual BCD counter circuits

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Simplified Circuit Diagram:

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Bread Board Implementation:
General Purpose PCB:

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Working of Counter from 0 to 9:

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Digital Works Simulation:

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Conclusion and Summary Of 0-9 BCD Counter:
 we have seen that a BCD Counter is a device that goes through a sequence of ten states
when it is clocked and returns to 0 after the count of 9. In our simple example above, the
input clock pulses are from a push button switch but counters can be used to count many
real-world events such as counting moving objects.
 However, suitable circuitry may be required to generate the electrical pulses for each
event to be counted as these events may occur at discrete time intervals or they may be
completely random.
 In many digital electronic circuits and applications, digital counters are implemented
using Toggle flip-flops or with any other type of flip-flop that can be connected to give
the required switching function, or with the use of dedicated counting IC’s such as the
74LS90. Binary counters are counters that go through a binary sequence and an n-bit
binary counter is made of “n” number of flip-flops counting from 0 to 2n-1.
 BCD counters follow a sequence of ten states and count using BCD numbers
from 0000to 1001 and then returns to 0000 and repeats. Such a counter must have at least
four flip-flops to represent each decimal digit, since a decimal digit is represented by a
binary code with at least four bits giving a MOD-10 count.
 We have also seen that the BCD coded output can be displayed using four LED’s or with
a digital display. But to display each number from 0 to 9 requires a decoder circuit, which
translates a binary coded number representation into the appropriate logic levels on each
of the display segments.
 Display decoder circuits can be constructed from combinational logic elements and there
are many dedicated integrated circuits on the market to perform this function such as the
74LS47 BCD to 7-segment decoder/driver IC.
 Most 7-segment displays are usually used in multi-digit counting applications so by
cascading together more BCD counters, 4-digit counters giving displays with a maximum
reading of 9999 can be constructed.
 The 74LS90 BCD Counter is a very flexible counting circuit and can be used as a
frequency divider or made to divide any whole number count from 2 to 9 by feeding the
appropriate outputs back to the IC’s Reset and Set inputs.

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Applications Of 0-9 Decade Counter:
 Bank Token Counters at cashier section.
 Couting system on automated production line.
 Digital Clocks
 Digital stop watches.
 Timers for automated water supply .
 Sensor controlled counters.
 Counting general objects in a any system.
Advantages :
 More Number of counters can be increased by increasing number of counter
IC and 7 segment displays.
 Cascading ensures that value of counter can be increased or decreased as per
applications and use.
 Counter Circuit can be used with other circuits to perform automated control
actions.
Disadvantages:
 As the number of counter size increases the complexity of building circuit
also increases.
 Costalso increases because the use of more ICs and 7 segments takes place.

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Datasheet of IC 74LS90

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Pin diagram Of IC74LS90:

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Pin Diagram of IC74LS47

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Datasheet of IC74LS47

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Future Scope and Improvements:
2-digit BCD Counter from 00 to 99
We Can improve our existing design by making changes by cascading more
counter IC and 7 segmentdisplays.

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References:
 http://www.electronics-tutorials.ws/counter/bcd-counter-circuit.html
 https://youtu.be/fU6sMNam2yM
 https://youtu.be/InvaoZduE4g
 https://youtu.be/2n7nM001Oi4
 http://www.electronicshub.org/decade-counterbcd-counter/
 Texas Instruments Datasheets IC 74LS90 andIC 74LS47
 http://www.daenotes.com/electronics/digital-electronics/counters-types-of-
counters
 https://en.wikipedia.org/wiki/Binary-coded_decimal