UNIVERSITY OF NAIROBI
FACULTY OF ENGINEERING
DEPARTMENT OF ELECTRICAL AND INFORMATION ENGINEERING
PEST MANAGEMENT SYSTEM USING ULTRASOUND
PROJECT INDEX: PRJ 080
BY
EDWIN NYAKUNDI MOKAYA
F17/1766/2006
SUPERVISOR: DR. G. KAMUCHA
EXAMINER: DR. V.K. ODUOL
PROJECT REPORT SUBMITTED IN PARTIAL FULFILMENT OF THE
REQUIREMENT FOR THE AWARD OF THE DEGREE
OF
BACHELOR OF SCIENCE IN ELECTRICAL AND ELECTRONICS ENGINEERING OF
THE UNIVERSITY OF NAIROBI 2011
Submitted on: 18 TH MAY, 2011
DEDICATION
I dedicate this project work to my father Joseph and mother Martha for their continued
inspiration, my brothers Denis and Eric, and my sister Doris for their prayers and
encouragement, and my niece Emy for a radiant presence. Thank you.
i
ACKNOWLEGEMENT
My gratitude goes out to Dr. G. Kamucha for his dedicated guidance on the technical aspects
of this project. Also to the technicians and lecturers in Department of Electrical and
Electronics Engineering for the skill they have helped me acquire over my five years course.
And to my proof readers Cyrus, Cornelius and Lydia. And to my classmates and friends.
Most of all I thank God.
ii
DECLARATION AND CERTIFICATION
Except where indicated and acknowledged, I certify that the information presented in this
report is my original effort and has not been presented before for a degree award in this or
any other university to the best of my knowledge.
…………………………………..............
EDWIN NYAKUNDI MOKAYA
F17/1766/2006
Date: ……………………
This report has been submitted to the Dept. of Electrical and Information Engineering,
University of Nairobi with my approval as supervisor:
………........………………………
Dr. G. Kamucha
Date: ……………………
iii
TABLE OF CONTENTS
DEDICATION ..................................................................................................................... i
ACKNOWLEGEMENT ..................................................................................................... ii
DECLARATION AND CERTIFICATION ...................................................................... iii
LIST OF FIGURES ........................................................................................................... vi
LIST OF TABLES AND GRAPHS ................................................................................. vii
ABSTRACT...................................................................................................................... viii
CHAPTER 1: INTRODUCTION ....................................................................................... 1
1.1 Problem Statement ....................................................................................................... 1
1.2 Objective ..................................................................................................................... 1
1.3 Report organisation ...................................................................................................... 1
CHAPTER2: STUDY OF DIFFERENT PEST MANAGEMENT METHODS ............... 2
2.1 Non-electronic pest control methods ............................................................................ 2
2.1.1 Physical methods ................................................................................................... 2
2.1.2 Bio-rational methods ............................................................................................. 2
2.1.3 Chemicals ............................................................................................................. 3
2.2 Electronic pest control methods-Ultrasound pest management ..................................... 3
CHAPTER 3: STUDY OF SPEAKERS WITH CAPACITY TO PRODUCE ULTRAFREQUENCY SIGNAL ..................................................................................................... 6
3.1 Cone tweeter ................................................................................................................ 6
3.2 Dome tweeter .............................................................................................................. 6
3.3 Piezo tweeter ............................................................................................................... 7
3.4 Ribbon tweeter............................................................................................................. 7
3.5 Electrostatic tweeter ..................................................................................................... 7
3.6 Planar-magnetic tweeter ............................................................................................... 7
3.7 ATM tweeter ............................................................................................................... 8
3.8 Horn tweeter ................................................................................................................ 8
3.9 Plasma or Ion tweeter................................................................................................... 8
CHAPTER 4: DESIGN OF CIRCUIT TO PRODUCE ULTRA SOUND ....................... 9
4.1 OSCILLATOR .......................................................................................................... 10
4.1.1 The 555 timer ...................................................................................................... 10
4.1.2 555-Timer terminals ............................................................................................ 10
4.1.3 555-Timer Oscillator circuit ................................................................................ 11
iv
4.1.4 Operation ............................................................................................................ 12
4.2 DECADE COUNTER ............................................................................................... 16
4.3 CLOCK GENERATOR ............................................................................................. 18
CHAPTER 5: SIMULATION RESULTS ........................................................................ 21
5.1 Clock-pulse generator ................................................................................................ 21
5.2 High Frequency Oscillator ......................................................................................... 22
5.3 Complete Circuit of Clock Pulse Generator, Decade Counter and High Frequency
Oscillator ......................................................................................................................... 25
CHAPTER 6: PRACTICAL RESULTS .......................................................................... 28
6.1 Timer circuit. ............................................................................................................. 28
6.2 Oscillator circuit ........................................................................................................ 28
6.3 Complete circuit ........................................................................................................ 28
CHAPTER 7: DISCUSSION AND CONCLUSION ........................................................ 30
7.1 Conclusion................................................................................................................. 30
7.2 Recommendation for future work............................................................................... 30
REFERENCES ..................................................................................................................... i
v
LIST OF FIGURES
Page
Figure 2.1: Sound Sensitivity of different animals
4
Figure 4.1: 555-Timer terminals
10
Figure 4.2: Circuit of a 555-Timer oscillator
12
Figure 4.3: 555-Timer oscillator waveforms
13
Figure 4.4: Figure of internal connection of flip-flops in a decade counter
17
Figure 4.5: Terminals of a Decade counter-4017
18
Figure 4.6: 555-Timer connected for low frequency oscillation
18
Figure 4.7: Flow chart of the different stages of the Ultrasound pest
management circuit
20
Figure 5.1: Simulation of clock pulse generator using a 555-Timer circuit
21
Figure 5.2: Simulation of high frequency oscillator
23
Figure 5.3: Simulation of modified high frequency oscillator
25
Figure 5.4: Complete circuit simulation
26
Figure 6.1: Complete connected circuit
28
Figure 6.2: Oscilloscope waveforms of complete circuit output
29
vi
LIST OF TABLES AND GRAPHS
page
Table 2.1: Hearing ranges of different species
4
Table 4.1: Table of operating states of a 555-Timer
11
Graph 4.1: Graph of frequency against capacitance for different values of
resistances
14
Table 4.2: Table of Different values of RA, RB and C and the calculated output
frequency
14
Table 4.3: Table of calculated value of RA to achieve desired frequency
15
Table 4.4: Table of Flip-flops outputs and resulting count
16
Table 4.5: Table of different capacitances and resistances and calculated output
frequency
19
Table 4.6: Table of output of different values of resistances
19
Table 5.1: Table of simulation results of different values of R1against calculated
results
22
Table 5.2: Simulation results of high frequency oscillator simulation circuit
23
Table 5.3: Table of new values of RA
24
Table 5.4: Table of simulation results of modified circuit
25
Table 6.1: Table of practical frequency oscillator results
28
vii
ABSTRACT
Pests are a nuisance to human habitation. They destroy structures, consume and contaminate
food and spread diseases. This gives rise to the need to control them.
The history of pest control probably began with the first human who ever swatted a mosquito
or picked off a louse. From the study of fossil records, it is known that most major pests
already existed by the time Homo sapiens first appeared on earth. But since our primitive
ancestors were hunters and gatherers, they probably found that insects were more useful as
food than they were troublesome as pests. It was probably not until the dawn of organized
agriculture, when insects attacked the plants we grew for food, that we first recognized them
as a potential threat to our own survival. [1]
Pest control methods have been evolving, from the physical dispersion of insects by our
ancestors, to current sophisticated methods of use of chemicals and other means. A more
advanced method is use of Ultrasound as a means of pest management. Ultrasound is sound
that is beyond the human hearing range i.e. having a frequency greater than 24 kHz. Insects
and other pests are capable of hearing sound within this range, thus a device can be made to
produce this sound which will repel the pests and not affect human beings.
The design of the Ultrasound pest management system involved designing a circuit with the
capacity to produce an electric signal in the ultra-frequency range. The circuit designed had
the capacity to produce signals of 40 kHz, 50 kHz, 60 kHz, 70 kHz and 80 kHz in that order.
This was desired since not all pests would be repelled with the same frequency sound. The
frequency of variation was about 1Hz.
viii
CHAPTER 1: INTRODUCTION
1.1 Problem statement
Pests are small animals or insects that destroy structures, consume and contaminate food and
spread diseases among many other negative attributes. For example, according to World
Health Organisation, malaria affects more than 200 million people annually of whom nearly
one million become fatal cases. In their statistics, a child dies every 45 seconds due to
Malaria in Africa. Malaria is transmitted exclusively through the bites of Anopheles
mosquitoes [2]. Also, many developing countries also struggle with inadequate food for their
populations. In many of these countries, between 40-50% of crops are lost to pests and
diseases. [3]
Thus control of pests is of immense importance and especially so in developing countries.
1.2 Objective
The objective of the project was to design and implement an ultrasound based system that
will repel pests such as mice and insects.
1.3 Report organisation
This project is organised into seven chapters:
·
Chapter one gives the introduction to the project and the project’s objective.
·
Chapter two is a study of the different pest management systems that are in use and a
detailed analysis of the advantages and disadvantages of an ultrasound pest
management system in comparison with other methods.
·
In chapter three is a study of different speaker/tweeter systems which have the
capacity to produce ultrasound.
·
Chapter four details the design of the circuit to produce the ultra-frequency signal.
·
Chapter five has the simulation results and redesign of the circuit due to the
simulation.
·
Chapter six gives the practical results as achieved in the laboratory with practical
components.
·
Chapter seven contains the conclusion and recommendations for future work. The
project report concludes with the appendix.
1
CHAPTER2: STUDY OF DIFFERENT PEST MANAGEMENT
METHODS
Pest management methods can be broadly classified in two groups;
·
Non-electronic pest control methods
·
Electric pest control methods
2.1 Non-electronic pest control methods
2.1.1 Physical methods
These involve the physical removal of pests from their location e.g. use of traps like rats traps
fall under this category of pest management methods. In case of insects in a farm, one may
physically remove the plant and replace it with another one that will not be affected by the
pest i.e. a pest resistant variety of the crop. [4] Use of a flywhisk by a butcher is also a
physical pest management method.
2.1.2 Bio-rational methods
Bio-rational methods can be divided into two groups. The first group is use of living
organisms that can kill the pest. The second group is naturally occurring biochemicals that
are harmful to the pest yet often are harmless to other living organisms. [4]
On the first method, insect pests frequently have natural enemies that are beneficial to the
landscape. These beneficial insects often exist in the landscape naturally, but they also can be
introduced. "Beneficials" may be predators or parasites. One common example of a beneficial
predator is the lady beetle. Both the larvae and adult lady beetles eat aphids and other softbodied insects. [4] Another common example is raring of cats in homes to prevent infestation
by rats and mice.
For the second method, an example of a naturally occurring biochemical is the bacterium
Bacillus thuringiensis (Bt). Bt contains a protein that is poisonous to specific insects and
harmless to other organisms. Bt can be sprayed on plants and insects which feed on the
sprayed portions of the plant will die. [4]
2
2.1.3 Chemicals
Chemicals used to control pests are called pesticides. Chemicals are usually used as the last
resort, but sometimes they are the most effective means of pest control. They work by
poisoning the pests. Some pesticides may be toxic to unintended organisms. Common
pesticides include rat poison to control rats and mice, and insecticides control insects such as
mosquitoes, houseflies and cockroaches. [4]
The above conventional methods have major setbacks. Physical methods can only be used in
small scale. Biorational methods are environmentally friendly, but in case of household pests,
only the rats and mice can be controlled while insects are left unchecked. And while use of
chemical is more effective, it comes with many health hazards as the chemicals might be
harmful to unintended organisms, including human beings. Some pesticides can only be
administered by trained personnel due to the huge danger they poise. And even household
insecticides like mosquito sprays have a nasty smell and their effectiveness wears off with
time.
A more revolutionary method of pest control is the electronic pest control in the use of
ultrasound.
2.2 Electronic pest control methods-Ultrasound pest management
Ultrasound is high frequency sound. Human beings have a hearing range of from 20Hz to
about 23,000Hz so that ultra sound is sound beyond 23 kHz. Human beings cannot hear
sound within the ultra sound range.
Figure 2.1 and table 2.1 show the sound sensitivity of different animals.
3
Figure 2.1: Sound Sensitivity of different animals
Table 2.1: Hearing ranges of different species
Species
Hearing Range
Human
64Hz-23,000Hz
Rat
200Hz-76,000Hz
Mouse
1,000Hz -91,000Hz
Mosquito
5Hz -80,000Hz
Housefly
10Hz -80,000Hz
Cockroach
3Hz-80,000Hz
Bat
2,000Hz -110,000Hz
Chicken
125Hz -2,000Hz
Goldfish
20Hz -3,000Hz
sheep
100Hz-30,000Hz
Ultrasound pest management makes use of the concept that different species have different
hearing ranges.
4
The use of ultrasound based pest management system comes with the following advantages:
·
It is non toxic and does not smell.
·
With mass production the device will be cheap.
·
Does not require repurchase and only occasional maintenance when fault occurs.
·
Can be made to operate from battery power and thus become portable and immune to
power shortages.
·
Does not kill the pests and merely repels them.
5
CHAPTER 3: STUDY OF SPEAKERS WITH CAPACITY TO
PRODUCE ULTRA-SOUND
Production of high frequency sound can be achieved through the use of tweeter. A tweeter is
a loudspeaker that has the capability to produce high frequency sounds. Tweeters that can
produce sound within the ultra range are called super tweeters. [5]
The tweeters operate using the same basic principle of a loudspeaker. A coil is suspended
within a fixed magnetic field. The coil is supplied with a current from an amplifier thereby
becoming energized. This energized coil forms a varying magnetic field which works against
the fixed magnetic field causing the coil to move. The coil is fixed to a diaphragm which
creates a sound as is vibrates within air. The mechanical movement of the coil resembles the
waveform of the current signal supplied coil. [5]
There are several types of tweeters;
3.1 Cone tweeter
A cone tweeter is simply a cone speaker optimized for high frequency capability.
These optimizations are; small size and light cone so as to enable rapid motion, stiff
cone material (e.g. ceramic cones), or materials with good damping properties (e.g.,
silk or coated fabric) or both, stiffer suspension (or spider) than for other driver thus
less flexibility which is required for high frequency reproduction, small coils (3/4 inch
is typical) and light (thin) wire, also to help the tweeter cone to move rapidly. Cone
Tweeters are relatively cheap but have poor dispersion properties. [5]
3.2 Dome tweeter
A dome tweeter is constructed by attaching a voice coil to a dome (made of woven
fabric, thin metal or other suitable material), which is attached to the magnet or the
top plate via a low compliance suspension. These tweeters typically do not have a
frame or basket, but a simple front plate attached to the magnet assembly. Dome
tweeters are categorized by their voice coil diameter, and range from 19 mm, through
38 mm. [5]
6
3.3 Piezo tweeter
A piezo (or piezo-electric) tweeter contains a piezoelectric crystal coupled to a
mechanical diaphragm. When a signal is applied to the crystal, the crystal responds by
flexing in proportion to the voltage applied across its surfaces, thus converting
electrical energy into mechanical. The conversion of electrical pulses to mechanical
vibrations and in turn the conversion of mechanical vibrations back into electrical
energy is the basis of piezo mechanism. The active piezo element is basically a
polarized material with some parts of the molecule positively charged and others
negatively charged, and with electrodes attached to two of its opposite faces. Some
materials used as the crystal are quartz (SiO2) and barium titanate (BaTiO3). [5]
3.4 Ribbon tweeter
Ribbon tweeters consist of a thin metal ribbon stretched between poles of a magnetic
structure with the magnetic field in the plane of the ribbon. A current is then passed
through the ribbon at right angles to the magnetic field resulting in a force normal to
the surface of the ribbon. Usually aluminium alloys are used for their relatively low
density and good electrical conductivity. The width of the ribbon is limited to about 1
cm in order to maintain a high field. Thus the efficiency of ribbon tweeters is about
10%, limiting the power outputs thus making them only useful in research. [6]
3.5 Electrostatic tweeter
Electrostatic tweeters/loudspeakers are sometimes known as high-voltage
loudspeakers. This is because they require a high polarization voltage, which is 1-3
kilovolts. These speakers consist of an insulating dielectric (air), a membrane (usually
plastic) which has a thin conductive layer, and electrodes on both sides of the
membrane. The current is applied to the electrodes which then drive the membrane.
At high frequencies the maximum power radiated reduces due to the mass reactance
of the membrane. [6]
3.6 Planar-magnetic tweeter
Some loudspeaker designers use a planar-magnetic tweeter, sometimes called a quasiribbon. Planar magnetic tweeters are generally less expensive than true ribbon
tweeters, but are not precisely equivalent because a metal foil ribbon is lighter than
7
the diaphragm in a planar magnetic tweeter and the magnetic structures are different.
Usually a thin piece of PET film or plastic with a voice coil wire running numerous
times vertically on the material is used. The magnet structure is less expensive than
for ribbon tweeters. The concept is most similar to that of electrostatic tweeters, with
the advantage that there is no DC voltage field needed as in electrostatics or arcing
thus does not attract dust. [5]
3.7 ATM tweeter
The Air Motion Transformer (ATM) tweeter works by pushing air out
perpendicularly from the pleated diaphragm. Its diaphragm is the folded pleats of film
around aluminium struts held in a strong magnetic field. In past decades, a series of
hybrid loudspeakers using such tweeters have been produced, along with conventional
woofers, referred to as Heil transducers after their inventor, Oskar Heil. They are
capable of considerable output levels and are rather sturdier than electrostatics or
ribbons, but have similar low-mass moving elements. [5]
3.8 Horn tweeter
A horn tweeter is any of the above tweeters coupled to a flared or horn structure.
Horns are used for two purposes; to control dispersion and to couple the tweeter
diaphragm to the air for higher efficiency. [5]
3.9 Plasma or Ion tweeter
Because ionized gas is electrically charged and so can be manipulated by a variable
electrical field, it is possible to use a small sphere of plasma as a tweeter. Such
tweeters are called a "plasma" tweeter or "ion" tweeter. They are more complex than
other tweeters, but offer the advantage that the moving 'diaphragm' is optimally low
mass, and so very responsive to the signal input. These types of tweeters are not
capable of high output, or of other than very high frequency reproduction, and so are
usually used at the throat of a horn structure to manage usable output levels. One
disadvantage is that the plasma arc typically produces ozone, a poison gas, in small
quantities as a by-product. [5]
8
CHAPTER 4: DESIGN OF CIRCUIT TO PRODUCE ULTRAFREQUENCY SIGNAL
To effectively repel a range of pests, it was desired that the ultra-sound circuit be able to
produce a signal with a varying frequency. The upper sound threshold for grasshoppers from
table is about 50 kHz and that for rodents and rats was in the range of 80 kHz. Thus it was
preferred that the circuit produced frequencies between 40 kHz to 80 kHz in steps of 10 kHz.
Thus; 40 kHz, 50 kHz, 60 kHz, 70 kHz and 80 kHz.
An extremely simple way to achieve a high frequency signal that would produce ultra sound
when fed to a tweeter would be to use a signal generator and set it to the desired frequency.
But signal generators are expensive and bulky, and it would be comical to have one in the
home for the sole purpose of repelling pests. Also, the change of frequencies will not be
automatic, requiring manual manipulation. Thus an electronic circuit was designed to
produce the ultra frequency signal. Electronic circuits are small, inexpensive and can be
designed to automatically switch between the desired frequencies. A circuit that produces a
repetitive or alternating electric waveform is called an oscillator.
Oscillators can either be made by use of individual components or use of integrated circuits,
ICs.
There are several circuits that make use of individual components to achieve oscillations.
Examples; Armstrong oscillator, Hartley circuit, Colpitts circuit and Clapp circuit. [8]
Use of IC was chosen due to the following advantages; [8]
·
Compactness. ICs are more compact that equivalent circuits made of transistors,
diodes, capacitors and resistors. This saves space.
·
High speed. Due to the fact that interconnections between components is physically
tiny, high switching speeds can be achieved as the electric charges require less time to
travel between the minimized spaces.
·
Low power requirement. ICs require very little current to operate, thus they will
produce less heat than their discrete-component equivalents.
·
Reliability. IC circuits have longer time spans due to the fact that all the components
are sealed within the IC case. This is in comparison to circuits made of discrete
components which are exposed to corrosion and intrusion of dust.
9
555 timer connected as an astable multivibrator can be used as an oscillator.
4.1 OSCILLATOR
4.1.1 The 555 timer
A 555 timer is functional block on IC that can perform several functions. Its working is as
follows; the output goes HIGH (a value close to Vcc) when the 555 timer receives a
TRIGGER input, and stays HIGH until the THRESHOLD input is driven at which point the
output goes LOW (a value close to ground) and the DISCHARGE is turned ON. The
TRIGGER input is by an input lever level above 1/3 Vcc, and the THRESHOLD is driven by
a signal at a level above 2/3 Vcc. [9]
Figure 4.1: 555-Timer terminals
A 555 timer can be used for precision timing, pulse generation, sequential timing, time delay
generation, pulse width modulation, pulse position modulation and linear ramp generation.
[9]
4.1.2 555-Timer terminals
Pin 1- Is the common/ground terminal. [11]
Pin 3- Output terminal. Can be a source or a sink. When a floating supply load is ON the
output is LOW and when OFF when the output is HIGH. A grounded load is ON when the
output is HIGH and OFF when the output is LOW. [11]
10
Pin 4- Reset terminal. It allows for the 555 timer to disable and override command signals to
the trigger input. When not to be used, it is connected to Vcc. When in use, it is grounded,
holding the output at LOW regardless of the input. [11]
Pin 5- Control voltage terminal. A 0.01 uF filter capacitor is usually connected from this
terminal to ground. The capacitor bypasses noise and/or ripple voltages from the power
supply to minimize their effect on the threshold voltage. The control voltage terminal may
also be used to change both the threshold and trigger voltages levels. [11]
Pin 2 and Pin 6- Trigger terminal and threshold terminal respectively. These two terminals
determine the state of the 555-Timer. The 555-Timer has two possible operation states and
one memory state. The Trigger input is compared with a lower threshold voltage that is
Vcc/3. The threshold input is compared with a higher threshold voltage that is 2Vcc/3. Table
4.1 shows the resulting states. [11]
Table 4.1: Table of operating states of a 555-Timer
Operating
Trigger pin 2
Threshold pin 6 State of terminals
State
Output 3
Discharge 7
A
Below VLT
Below VUT
HIGH
OPEN
B
Below VLT
Above VUT
HIGH
OPEN
C
Above VLT
Below VUT
REMEMBERS LAST STATE
D
Above VLT
Above VUT
LOW
GROUNDED
Pin 7- Discharge terminal. Used to discharge an external timing capacitor during the time the
output is LOW. When the output is high, this pin acts like an open circuit and allows the
externally connected capacitor to charge through an externally connected resistor. [11]
Pin 8- Positive supply voltage, Vcc. Can vary from +5V (when powered by existing digital
logic supplies) to +18V (when powered by linear IC supplies). [11]
4.1.3 555-Timer Oscillator circuit
Figure 4.2 shows a 555 timer connected to as an oscillator. In this mode of operation, the
capacitor, C, charges and discharges between 1/3 Vcc and 2/3 Vcc. The charge and discharge
times, and therefore the frequency of operation, are independent of the supply voltage. [10]
11
Figure 4.2: Circuit of a 555-Timer oscillator
4.1.4 Operation
Initially, pins 2 and 6 are below VLT and output pin 3 goes HIGH and pin 7 is OPEN so
capacitor C charges through RA and RB. This is state A. The capacitor charges beyond
1/3VCC. In the region between VCC /3 and 2 VCC /3, the 555 timer is in state C, memory state.
It thus remembers the previous HIGH state and remains HIGH. When capacitor voltage, VC,
goes just above VUT (2Vcc/3), the 555 timer enters state D and the output goes LOW. Thus
pin 7 becomes a short circuit to ground and capacitor discharged through RB. During the
discharge period when VC is between Vcc/3 and 2 VCC /3, the timer is in state C and
remembers the previous state, thus output stays LOW. When Vc drops below VLT the
sequence repeats itself and oscillation occurs. [11]
Waveforms generated in this mode of operation are as in figure 4.3; top trace is the output
waveform, bottom trace is the capacitor voltage.
12
Figure 4.3: 555-Timer oscillator waveforms
Discharge equation starting at 2/3 Vcc is given by
(4.1)
The capacitor discharges to 1/3 Vcc at time =tD so that
(4.2)
Thus,
.
.
(4.3)
Thus charge time (output high) is given by:
.
(4.4)
And the discharge time (output low) by:
.
(4.5)
Thus the total period is:
.
(4.6)
And the frequency of oscillation is:
13
.
(4.7)
Easy determination of R and C values can be done by the following graph [8]
Graph 4.1: Graph of frequency against capacitance for different values of resistances
Table 4.2 shows different values of RA, RB and C and the resulting frequencies.
Table 4.2: Table of Different values of RA, RB and C and the calculated output frequency
555 oscillator frequencies
RB = 10k
RB = 100k
RB = 1M
RA = 1k
RA = 10k
RA = 100k
0.001µF
68 kHz
6.8 kHz
680Hz
0.01µF
6.8 kHz
680Hz
68Hz
0.1µF
680Hz
68Hz
6.8Hz
1µF
68Hz
6.8Hz
0.68Hz
10µF
6.8Hz
0.68Hz
0.068Hz
(41 per min.)
(4 per min.)
C
Example
14
=
=
=
.
+
(
)
.
+
x
.
µ
=
A 555-timer connected in the oscillation mode produce a single frequency waveform
determined by values of RA, RB and C. As stated previously, different pests are most
effectively repelled at different frequencies. Thus there should be a means for the circuit to
change frequencies of the output signal.
From the study of hearing capabilities of different animals, a range of frequencies from 40
kHz (upper band of grasshoppers) to 80 kHz (upper band of houseflies and rodents) was seen
to be most ideal. Intervals of 10 kHz would mean 5 steps i.e. 40 kHz, 50 kHz, 60 kHz, 70
kHz, and 80 kHz.
Since we want frequencies in the region of 40-80 kHz, C is chosen to be 0.001 µF.
There was a choice to vary either RA or RB. The position of RA in the circuit makes it easier
to vary compared to RB as it hangs i.e. one side is connected to pin 7 and the other to the
biasing voltage, compared to RB which is connected to pin 7 and pin 8 on either side.
Table 4.3: Table of calculated value of RA to achieve desired frequency
Frequency
Capacitor C
RA (ohms)
RB (ohms)
40 kHz
1nF
24k
6k
50 kHz
1nF
16.8k
6k
60 kHz
1nF
12k
6k
70 kHz
1nF
8.5k
6k
80 kHz
1nF
6k
6k
Example
=
=
=
.
+
(
)
.
+
.
15
µ
=
A simple way to achieve variation in the value of RA would be to use a decade counter where
each of the sequential outputs is connected to a resistor with the required value of RA.
4.2 DECADE COUNTER
A decade counter is a Binary Count-Down (BCD) counter which counts from 0 to 9 then
returns to 0. The term counter is used to describe a register that goes through a prescribed
sequence of states upon the application of input pulses. The input pulses may be clock pulses
or may originate from some external source and occur at fixed or random intervals of time.
[12]
Further, a decade counter belongs to the family of binary ripple counters. These counters
consist of a series connections of flip-flops, with the output of each flip-flop connected to the
Clock input of the next higher order flip-flop. The flip-flop holding the least significant bit
receives the incoming count pulses. [12]
Table 4.4: Table of Flip-flops outputs and resulting count
Flip-Flop Outputs
Decimal Digit
D
C
B
A
0
0
0
0
0
0
0
0
1
1
0
0
1
0
2
0
0
1
1
3
0
1
0
0
4
0
1
0
1
5
0
1
1
0
6
0
1
1
1
7
1
0
0
0
8
1
0
0
1
9
16
Figure 4.4: Figure of internal connection of flip-flops in a decade counter
Figure above shows the J-K flip-flop connections in a decade counter. The four outputs are
designated A, B, C and D, with A having the least significant bit. The clock of FF1 is
connected to the counting pulse. Since the J and K pins are connected to a HIGH, when the
clock goes from 1 to 0, the flip-flop is complemented, meaning it’s output goes to 1, and
when it goes from 0 to 1, the output of FF1 goes to 0. Thus the output A of FF1 is as shown.
FF2 receives its clock pulse from the output A of FF1. When A goes from 1 to 0, the output B
of FF2 is complemented. Thus it takes twice as long to change state compared to A.
FF3 receives its clock pulse from FF2 and thus its output C takes twice as long as B to
change state.
FF4 receives its clock pulse from FF3 and thus its output D takes twice as long as C to
change state.
The NAND gate is connected to B and D. When both B and B are high, the output of the
NAND gate is low, thus clearing all the flip-flops and the counting starts again.
17
Figure 4.5: Terminals of a Decade counter-4017
The duration of each output pin remaining HIGH depends on the frequency of the input
clock. A 555timer connected as a low frequency oscillator was used to generate the clock.
4.3 CLOCK GENERATOR
The 555-timer was connected as the timer circuit. This was because the IC was already used
as the oscillator and its reuse would create economies of scale.
Figure 4.6: 555-Timer connected for low frequency oscillation
From previous treatment of charge and discharge time of a 555 timer, charge time is give
by
.
(4.8)
And the discharge time by:
18
.
(4.9)
Thus the total period is:
.
.
(4.10)
And the frequency of oscillation is:
.
(4.11)
Table 4.5 shows the different values of C1 and R1 and resulting calculated output
frequencies
Table 4.5: Table of different capacitances and resistances and calculated output
frequency
R1 = 10k
R1 = 100k
R1 = 1M
R1 = 10M
0.001µF
71630Hz
7163Hz
716.3Hz
71.63Hz
0.01µF
7163Hz
716.3Hz
71.63Hz
7.163Hz
0.1µF
716.3Hz
71.63Hz
1µF
71.63Hz
7.163Hz
0.7163Hz
0.07163Hz
10µF
7.163Hz
0.7163Hz
0.07163Hz
0.007163Hz
C1
7.163Hz
(43 per min)
(430 per min)
0.7163Hz
(25 per hour)
(4 per min)
1µF capacitor for C1was chosen. For different values of R1, the calculated output
frequency using formula above is;
Table 4.6: Table of output of different values of resistances
R1
C1
Calculated Output Frequency
10k
0.1µF
71.63Hz
50k
0.1µF
14.33Hz
100k
0.1µF
7.16Hz
200k
0.1µF
3.58Hz
300k
0.1µF
2.39Hz
400k
0.1µF
1.79Hz
19
500k
0.1µF
1.43Hz
1M
0.1µF
0.72Hz
FLOW DIAGRAM
CLOCKPULSE
GENERATOR
DECADE
COUNTER
OSCILLATOR
(555-TIMER)
TWEETER
Figure 4.7: Flow chart of the different stages of the Ultrasound pest management circuit
20
CHAPTER 5: SIMULATION RESULTS
First, the separate circuits i.e. timing circuit and oscillator circuit were simulated using
National Instruments Multisim version 10.0.1 Education edition. Then the complete circuit
was simulated.
Simulation Results
5.1 Clock-pulse generator
Circuit was simulated as shown in figure 5.1
Figure 5.1: Simulation of clock pulse generator using a 555-Timer circuit
21
A 1µF capacitor was used as C1 due to the range of frequencies it provided. Different values
of were simulated and the results tabulated in table 5.1
Table 5.1: Table of simulation results of different values of R1against calculated results.
R1
C1
Calculated Output
Simulation Output
Simulation Output
Frequency
Frequency
signal period
10k
1µF
71.63Hz
72.1Hz
1.39ms
50k
1µF
14.33Hz
13.8Hz
7.25ms
100k
1µF
7.16Hz
7.0Hz
14.29ms
200k
1µF
3.58Hz
3.42Hz
29.24ms
300k
1µF
2.39Hz
2.4Hz
41.67ms
400k
1µF
1.79Hz
1.63Hz
61.34ms
500k
1µF
1.43Hz
1.5Hz
66.67ms
1M
1µF
0.72Hz
0.7Hz
1.43s
Clocking frequency of around 1Hz was desired. The 1M resistor was chosen to be used in the
main circuit.
5.2 High Frequency Oscillator
Circuit in figure 5.2 was simulated.
22
Figure 5.2: Simulation of high frequency oscillator
Table 5.2: Simulation results of high frequency oscillator simulation circuit
Capacitor C
RA
RB
Calculated Frequency
Simulation Frequency
1nF
24k
6k
40 kHz
25.4 kHz
1nF
16.8k
6k
50 kHz
28.8 kHz
1nF
12k
6k
60 kHz
34.1 kHz
1nF
8.5k
6k
70 kHz
38.1 kHz
1nF
6k
6k
80 kHz
41.1 kHz
The circuit did not produce the desired frequencies. This was speculated to be due to the fact
that during charge, the terminal 7 (discharge) was not an ideal open circuit thus leading to an
increased charge time and therefore the simulated frequency was lower than expected e.g.
instead of 40kHz, what was achieved was 25.4kHz.
23
A solution was devised as connecting a diode across RB. During charge time, the current
will bypass RB and charge the capacitor through RA and the diode. During discharge the
capacitor discharges through resistor RB. Thus the time and hence frequency now
depends on RA and C.
New formulas are.
.
(5.1)
And the discharge time (output low) is given by:
.
(5.2)
Thus the total period is:
.
= .
(5.3)
And the frequency of oscillation is:
.
(5.4)
Values of RA From calculation
Table 5.3: Table of new values of RA
Frequency
Capacitor C
RA
40 kHz
1nF
18k
50 kHz
1nF
14.4k
60 kHz
1nF
12k
70 kHz
1nF
10.3k
80 kHz
1nF
9k
Circuit was simulated as shown in figure 5.3
24
Figure 5.3: Simulation of modified high frequency oscillator
Simulation frequency results
Table 5.4: Table of simulation results of modified circuit
Capacitor C
RA
RB
Calculated Frequency
Simulation Frequency
1nF
18k
6k
40 kHz
41.6 kHz
1nF
14.4k
6k
50 kHz
49.5 kHz
1nF
12k
6k
60 kHz
61.3 kHz
1nF
10.3k
6k
70 kHz
71.3kHz
1nF
9k
6k
80 kHz
83.5 kHz
5.3 Complete Circuit of Clock Pulse Generator, Decade Counter and High
Frequency Oscillator
25
Figure 5.4: Complete circuit simulation
26
The output of the circuit had frequencies between 41.6kHz and 83.5kHz. The frequency
varied in five steps.
27
CHAPTER 6: PRACTICAL RESULTS
6.1 Timer circuit.
R1=1M
and C1=1µF
Vcc=12V
Vo=11.48V
6.2 Oscillator circuit
Instead of diodes 1BH62 being used, diodes IN4148 were used. Both are signal diodes.
Close valued resistors were used also instead of the calculation and simulation resistors.
Capacitor C
RA
RB
Required Frequency
Actual achieved Frequency
1.12nF
17.88k
5.66k
40kHz
38.9kHz
1.12nF
15.00k
5.66k
50kHz
47.8kHz
1.12nF
12.02k
5.66k
60kHz
59.7kHz
1.12nF
9.95k
5.66k
70kHz
68.3kHz
1.12nF
8.17k
5.66k
80kHz
79.2kHz
6.3 Complete circuit
Figure 6.1: Complete connected circuit
28
Figure 6.2: Oscilloscope waveforms of High freq. Oscillator output
Vcc =12V
Vo (oscillator) =11.36V
Resistance of Piezo tweeter =4
Current Io = Vo /R=11.36/4=2.84A
Output power = Vo Io =11.48X2.87 =32.26Watts
Frequency of Vo changed approximately every 1s.
29
CHAPTER 7: DISCUSSION AND CONCLUSION
7.1 Conclusion
The design of an ultrasound pest management system was done successfully. The electronic
circuit was designed and tested. It produced signals of frequencies 40kHz, 50kHz, 60kHz,
70kHz and 80kHz, which are in the ultrasound range and are irritating to pests such as mice
and insects. The output signal was found to be of about 32 watts when connected to a 4 ohms
piezo tweeter.
7.2 Recommendation for future work
The super tweeters with the capacity to produce ultrasound (above 24kHz) are not readily
available in the market. Thus manufacturers and developers should invest in the production of
such super tweeters which have high efficiency and are low cost.
For mass production of these ultrasound pest management systems for end use, a circuit that
steps down main power supply and converts it to 12V dc will be required to be incorporated
into the system to supply the 12V dc required as Vcc for the system ICs. This will enable the
ultrasound pest management system to operate from mains sockets.
30
REFERENCES
[1]
John R. Meyer, “Introduction to Pest Control Tactics”, Department of Entomology
NC State University, 2003.
[2]
http://www.who.int/mediacentre/factsheets, retrieved on 21st January 2011.
[3]
http://www.cabi.org, retrieved on 21 st January 2011.
[4]
Stevie Daniels, Gregory Hoover, "Pest Management Methods, Creating Healthy
Landscapes”, Penn State College of Agricultural Sciences, The Pennsylvania State
University, Publications Distribution Center, Fact Sheet (#7), 2008.
[5]
www.wikipedia.org/tweeter, retrieved on 18th January 2011.
[6]
R.W. Leonard, Encyclopedia of Physics; Acoustics -Generation and Measurement
of Sound in Gases, Springer-Verlag, 1962.
[7]
A. Barone, Encyclopedia of Physics; Acoustics - Generation, Detection and
Measurement of Ultrasound, Springer-Verlag, 1962.
[8]
Stan Gilbilisco, Teach Yourself Electricity and Electronics, Third Edition,
McGraw-Hill, 2002.
[9]
Paul Horowitz, Winfield Hill; The Art of Electronics, Second Edition, Cambridge
University Press, 1980.
[10]
National Semiconductor , LM 555 Timer, July 2006.
[11]
Robert F. Coughlin, Fredrick F. Driscoll, Operational Amplifiers and Linear
Integrated Circuits, Fourth Edition, Prentice-Hall, 1991.
[12]
M. Morris Mano, Michael D. Ciletti, Digital Design, Fourth Edition, Prentice-Hall,
2007.
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