CHAPTER ONE

INTRODUCTION

1.0 Background of the Study

Counting has been a crucial activity to human beings from remote antiquity.

Counting is done for different purposes e.g. recording, planning, classifying…etc. Our

ancestors relied on their brain and physical senses to do the count. However, as noted

by Microsoft Encarta Encyclopedia (2005): “People can typically remember about

seven items (plus and minus two) from a random list.” This statement shows the

unreliability of the human brain. Broadbent, a psychologist equated the brain to a

communication channel with a limited throughput capacity. This is why beyond 100,

counting becomes difficult and the possibility of making mistakes increases. The same

thing happen when the speed of count is increased or the items being counted move at

a certain speed.

Faced with these setbacks, scientists and technologists began to do researches on

how to discover a better way of counting i.e. a machine that could count faster and

more accurately than humans. It was during the mid 17th century that a mechanical

counting machine, which uses rotating shafts and gears, was invented. This type with

little improvement was used up to the late 19th century (Wilson, 2004). However, the

mechanical counters had drawbacks as any other mechanical device such as frictions,

rust and wear to mention but a few. Eventually more researches were carried out and

in 1932 the first binary electronic counter using thyratron tubes was invented. It was

bulky and power consuming. With the advent of transistors in 1948 and Integrated

circuits (ICs) in 1960, counters in much smaller units were constructed. In 1970 even

smaller counters were achieved through microprocessors.

Since then, with the constant advancement in electronics,” many different kind of

counter ICs have been designed, leaving the circuit designer with only the task of

selecting the particular IC that best suits his needs.” (Bigelow, 2006)

Across the world, people generally count numbers or events using the decimal

system. That is why decade or decimal counters are so important. In general, a

decimal or decade counter is a device, which stores (and sometimes displays in

decimal form) the number of times a particular event or process has occurred

(Wikipedia, the free Encyclopedia, 2007).

There are two types of decimal counters:

i) The decade up counter

ii) The decade down counter

Both counters are important in several applications and the difference between

them is that the up counter counts up i.e. from zero to nine (or lowest number to

highest number) whereas the down counter counts in the opposite. The up-counter is

mostly used in many applications such as manufacturing industries, filling stations

and banks (to mention a few) where up-counting is one of the major activities.

The problem faced in many of such establishments where precision and accuracy

of count are crucial is that the possibility of ‘over count’ when a counting machine is

to be stopped by a human is always there. For instance, if in a manufacturing industry

exactly 100 goods are to be conveyed in a place at a time by a machine; and a digital

counter counts the goods up to 100; it will be easy for the operator to stop the machine

at exactly 100 if the counting is not fast. However, if the counting is fast, it becomes

difficult for the operator to stop the machine at exactly 100. In this case, a

programmable device that will automatically send the stop signal to the machine at

exactly 100 counts is necessary.

This is the reason why this study seeks to design and construct a programmable

decade counter that can be used to make a precise count of items, events or people and

stop automatically after the preset count.

The programmable decade up counter stores the preset number of counts and

compares it with the new count. If they are equal, the counter activates the output

transducer and automatically stops counting.

1.1 Statement of the Problem

Precise, programmable and auto-stop counting is very important in most

companies, industries and establishments. According to Bigelow (2006:2): “when

selecting a counter to be used in a manufacturing or production line, accuracy and

precision are the most important parameters.” Humans generally find it difficult to

count at a fast rate or grasp fast moving objects. For that reason it is difficult for them

to stop a fast running counter at a particular count.

The Researcher is therefore out to produce a digital electronic device that will be

able to automatically stop its count when it reaches the precise number, pre-

programmed or set by the user. This is in order to alleviate the problems of:

i) The inability of humans to stop a fast running counter at a particular count.

i) The non auto-stop of a machine at a precise number of items to be produced or

allowed (as the case may be) in a production line.

iii) The inaccurate count of a preset number of fast moving objects.

1.2 Purpose of the Study

The purpose of this study is to design and construct a digital electronic device that

will ensure a precise number of counts of items, events or people and stop

automatically when the preset count has been attained. This was conceived out of the

unreliability of humans in manually stopping a fast running counter when the precise

number of count has been reached.

This study aims at:

i) Designing a digital electronic up counter with programmable final count.

ii) Constructing a digital electronic device using commonly available components.

iii) Designing and constructing effective equipment capable of displaying the counts.

1.3 Significance of the Study

This study is vast in utility. It will be useful in banking sectors in the counting of a

specified amount of cash needed at a time. Manufacturing Industries and companies

(Breweries, pharmaceuticals, processing plants, etc.) will find it useful when used in

connection with their production and packaging lines, especially if a precise number

of items is expected to be produced or packaged at a time. The device can also be used

in many applications requiring precise timing, as time bombs, speedometers, on/off

timers. Filling stations and the like can incorporate it in their meters. This will prevent

undercounts and overcounts and satisfy both seller and buyer.

Hotels and industries with multilevel structures (sky scrapers) can also use it in

their lifts for precision of the particular floor one is intending to go. Schools can also

use it to determine the number of people that should enter a class in a day. When the

number is reached, the door closes automatically. Educators will also use it as

instructional media.

Finally, it will eradicate the problem encountered by human beings in trying to

manually stop a fast running counter at a specified count.

1.4 Delimitation of the Study

Other digital integrated circuit families such as Resistor-Transistor-Logic (RTL)

and Diode-Transistor-Logic (DTL) could as well be used to design the study. More so,

there are digital decade up-counters with more than four digits. However this study

has been restricted to the use of Transistor-Transistor-Logic (TTL) and

Complimentary Metal Oxide Semiconductor (CMOS) devices for easy interfacing and

four digits in order to reduce construction cost.

1.5 Limitation of the Study

The Researcher intended to design and construct a minimized, low power-

consuming device, which will have a wide range of application. However, because the

components and materials used were locally sourced, there is limitation in its

application. It cannot be used where micro or miniature size is of utmost importance.

1.6 Definition of Terms

i) Data Book: A book that describes the configuration and ratings of components.

ii) Decade Counter: An electronic device that counts in base ten.

iii) Magnitude Comparator: An electronic device that compares two binary

numbers.

CHAPTER TWO

REVIEW OF RELATED LITTERATURE

2.0 Introduction

This chapter review literatures that are related to the study under the following

subheadings:

i) Brief history of Counters

ii) Details on the programmable digital decade up counter

iii) Previous projects on digital decade up-counters

2.1 Brief History of Counters

Counting is a long age activity. In remote antiquity, our ancestors using their brain

and physical senses did counting. It was time consuming and inaccurate especially

when the counting was fast and numerous: practically impossible if the objects being

counted moved at a frequency, which the human eye failed to perceive (Microsoft

Encarta Encyclopedia, 2005).

These inabilities propelled scientists and technologists to go on researches and in

mid 17th century a mechanical counting machine using rotating shafts and gears was

invented. It became the major counting device till in the late 19th century. (Wilson,

2004) However the disadvantages posed by the machine such as friction, rust and

wear lead humans into more researches and in 1932 E.Wynn-Williams, at Cambridge,

England, used thyratron tubes to construct the first binary digital counter, for use in

connection with physics experiments. The counter was later improved by replacing

thyratron tubes by vacuum tubes in 1945. Their disadvantage was that of bulkiness

and high power consumption.

In the late 1950 transistors were discovered and used to replace vacuum tubes.

These new developments lead to a reduction in the size and power consumption of

digital counters. In the late 1960, IC was introduced and in 1970 Microprocessors

became a reality. (Microsoft Encarta Encyclopedia, 2005) The discovery of ICs and

Microprocessors lead to the “design of different kind of Counter ICs, with a vast list

of capabilities leaving the circuit designer with only the task of selecting the particular

IC that best suits the need.” (Bigelow, 2006)

2.2 Details on the Programmable Digital Decade Up-Counter

2.2.0 Definitions

Josef et al (1996) defines counting as “the continuous adding or subtracting and

storing of binary values. The Wikipedia Free Encyclopedia (2007) defines a counter

as “a device, which stores (and sometimes displays) the number of times a particular

event or process has occurred, often in relationship to a clock signal.” GlobalSpec

(2007) defines digital counters as “integrated circuits that counts events in computers

and other digital systems.”

From these definitions it can be inferred that:

A) A counter consists of three parts: a clock signal, a store or memory, and a display

or readout of the counts.

B) There are generally two types of counters:

i) Up-counters, which count by adding a unit to a stored sum and stores the new

sum.

ii) Down-counters, which subtract a unit from a stored sum and stores the new sum.

The Wikipedia Free Encyclopedia (2007) further classifies the two types of

counters into binary and binary coded decimal (BCD or Decade) counters. The

difference between the two being that: the Decade counter counts in tens rather than

having a binary representation.

Merging all these definitions together, we can define a digital programmable

decade up-counter as an electronic device that counts in base ten from zero up to the

preprogrammed count and stops automatically.

The Four Digit Programmable Decade Up-Counter has all the stages described

above i.e. input, store or memory and display readout as we can see from the block

diagram below, in fig2.1.

2.2.1 Principle of Operation of a Programmable Decade Up-Counter

As we see in the block diagram, the input device consists of a square wave

oscillator used to preset the counter and a sensor, which senses events, items or

people to be counted. The input sends the clock signal to the counter whose counts

(output) can be read directly through the display devices. After the oscillator is used

to preset the count, the preset count is stored in the memory devices. Any new count

is compared with the preset count by the comparators; which send a command signal

to the stop mechanism when the new count is equal to the preset count. Once this is

done, the stop mechanism prevents any further count.

2.2.2 Details on the Programmable Decade Up-Counter

The stages of the counter are six excluding the power supply section. We shall

review related literature to each stage.

2.2.2.1 The Input Devices

The input device is made up of a square wave oscillator and a light sensor.

i) A square wave oscillator is an electronic device that generates a varying

output signal is similar to a square shape. According to Josef et al (1996:2), “ac

voltages with a square waveform have become of considerable importance as clock

pulse and control signals.” Square wave oscillators can be constructed using

transistors and ICs. The IC type is more reliable and more stable than the

transistor type (Floyd, 1996)

An example of a square wave oscillator using an operational amplifier is shown

below in fig 2.2. The capacitor C1 and resistor R1 determine the frequency of

oscillation (the switching of the output from low to high),and resistor R determines

the charging and discharging of the capacitor.

ii) Light sensor is an electronic device whose electrical characteristics are

affected by the presence and intensity of light. A light sensor becomes active or

inactive with the presence of light. Microsoft Encarta Encyclopedia (2005) lists

different types of light sensors as photodiodes, phototransistors, light dependant

resistors (LDR or photo resistors), light activated silicon controlled rectifiers

(LASCR) and phototriacs. However, as pointed out by The Wikipedia free

Encyclopedia (2007); the LDR is the most common and cheapest. The LDR combined

with an operational amplifier and a light source as shown in fig 2.3 below, is

an effective input sensor/clock signal for digital circuits.

2.2.2 Decade Up-Counters

According to GlobalSpec (2007), “digital counters are available in a variety of

IC package types and with different numbers of pins and flip-flops; and the list of

capabilities and option is quite large, leaving the circuit designer with only the task of

selecting the particular IC that best suits the need.’ (Bigelow, 2006:2).

74HCT390 is a decade up-counter; cheap, reliable, and low-power consuming. It

has two-decade up-counters, which make it good for any design where two will

largely suffice. (Texas Instrument, 1990) The proposed circuit diagram of a sample

counter using this device is shown below. The counting sequence follows that of a

BCD with “H” standing for a high logic level (1), and “L” standing for a low logic

level (0). As we can see the counting is done in an ascending order; from “LLLL” to

“HLLH” (i.e. 0000 to 1001), which are the binary equivalent of numbers 0 and 9.

2.2.3 Display Devices.

The display device is a combination of a BCD to Decimal decoder, and a 7-

segment Light Emitting Diode (LED) display. The decoders are sometimes called 7-

segment display drivers.

Hewes (2007:6) described the operation of the display drivers thus: “the inputs

A-D of a display driver are connected to the BCD (Binary Coded Decimal) outputs

(A-D) from a decade counter. The display makes its outputs a-g become high or low

as appropriate to light the required segments a-g of a 7-segments display.” Nave

(2007) gives an example of the Interconnection between 74HC48 Display Driver

(decoder) and a 7-segment LED display, as shown below:

Fig 2.5 74HC90 Counter, 7-segment LED Display, and its Display Driver

74HC48

2.2.4 The Memory Devices

The memory devices are similar to shift registers. Maddock and Calcutt

(1998:265) define register as “a group of flip-flops (multivibrators) used to store

binary data.” They went ahead to note that when the data stored in the register can be

shifted from one storage location to another by a control signal, and then the register

is referred to as shift register.

The Wikipedia Free Encyclopedia (2007) rated the D-type flip-flop as the

mostly used for shift registers because of its fewer inputs compared to JK and RS

flip-flops. For instance, it is easy to find 8 D-flip-flops (e.g. 74HCT374) as shown

below by Philips Semiconductors than it is obtainable with JK and RS types.

2.2.5 Magnitude Comparators

The TTL data book for design engineers defines magnitude comparators as

“digital electronics devices that performs straight binary and straight BCD data.”

Such device has two sets of inputs and three outputs (>, <, =) to indicate the

comparison between them. Philips Semiconductors describe the operation of

74HCT85 magnitude comparator thus “When two binary numbers A and B are equal,

the output A=B will be activated. If number A is greater than number B, the output

A>B will be activated. It applies also to output A<B.” The sample circuit for the

comparison of two binary data is shown in fig 2.7 below.

2.3 Previous Researches on Decade Up-Counters

G. Fait constructed a 1 digit Decade Up-Counter in 1984. He had a good design,

which includes adjustable counter speed and a 7segment display of the counts. The

drawbacks in his designs were:

i) It has only one digit

ii) There is no provision for presetting the final count

iii) It has no input count sensor.

Wikipedia gives us a one digit up decade counter with digital readout. His

model makes use of 4 ICs for only one-decade count. This makes it power

consuming and unnecessarily bulky. Like the former, it makes no provision for

presetting the count, as has no input sensor.

Danladi B. Idris incorporated a 3digit decade Up-Counter in Rewinding Machine

in 2004. His model could count up to 999, had a 3digit display and an Input Sensor.

Its limitations are: only 3digit display and no provision for a programmable count

hence no auto stop.

Summary

In this chapter related literature to the study were reviewed. The Researcher

traced literature on: the history of counters; details of different stages of a

programmable decade Up-Counter and three past researches on a decade Up-

Counters. The major limitation of those researches is their lack of provision for a

programmable final count. The Researcher’s device is expected to overcome this

limitation.