ABSTRACT

ABSTRACT

Audiometry is the technique to identify and quantitatively determine the degree of hearing loss of a person by measuring his or her hearing sensitivity, so that suitable medical treatment or one of the appropriate hearing aids and assistive devices can be prescribed. In audiological investigations, the hearing sensitivity is tested for pure tones, speech or other sound stimuli. The result, when plotted graphically, is called an audiogram. The electronic instrument used for measuring the hearing threshold level is called an audiometer. Using it, the test tones of different frequencies and levels are generated and presented to the patient and hearing thresholds are determined on the basis of patient’s response. The auditory system and its disorders are described. Audiometric test is discussed.

TABLE OF CONTENTS

CHAPTER NO.TITLE PAGE NO.

ABSTRACT v

LIST OF TABLEix

LIST OF FIGURESx

1.INTRODUCTION1

1.1 ABOUT THE PROJECT1

1.2ORGANIZATION PROFILE3

2.PHYSIOLOGY OF THE AUDITORY SYSTEM4 2.1 CAUSES FOR HEARING LOSS 6

3. HEARING TESTS 8

3.1 PURE TONE AIR CONDUCTION

THRESHOLD TESTING9

3.2 REPRESENTATION OF SOUND10

3.3 AUDIOGRAM10

4. BLOCK DIAGRAM OF THE AUDIOMETER14

4.1 BLOCK DIAGRAM DESCRIPTION15

5.HARDWARE16

5.1 POWER SUPPLY16

5.1.1 Linear Mode Power Supply16

5.2 FUNCTION GENERATOR19

5.2.1Circuit Description22

5.2.1.1 Setting Up23

5.2.2IC 8038 Description23

5.2.2.1 Features23

5.3 PRE AMPLIFIER25

5.3.1Circuit Description26

5.3.2 IC LM324 Description27

5.3.2.1 Features27

5.3.2.2 Unique Characteristics28

5.3.2.3 Advantages28

5.4 POWER AMPLIFIER29

5.4.1 Circuit Description30

5.4.2 IC LM386 Description31

5.4.2.1 Features31

5.5 ATTENUATOR CONTROL32

5.6 HEADPHONE34

5.7 CLAMPER CIRCUIT35

5.7.1 Positive Clamper35

5.8 ADC37

5.8.1 Successive Approximation ADC38

5.8.1.1 Operation39

5.8.2 Connection Diagram of ADC080442

5.8.3 IC ADC0804 Description43

5.8.3.1 Features43

6.SOFTWARE44

6.1 INTRODUCTION TO EMBEDDED SYSTEM44

6.2 IC 89C51 MICROCONTROLLER45

6.2.1 Features46

6.2.2Description46

7.LIQUID CRYSTAL DISPLAY48

8. CONCLUSION49

9. APPENDICIES 50

9.1APPENDIX 150

9.2APPENDIX 251

9.3APPENDIX 359

10.REFERENCES82

LIST OF TABLES

NO.TITLE PAGE NO.

1. Relation between Hearing Thresholds and

Degree of Hearing Loss (for adults)13

2. Relation between Regulator Names and its

Output Voltages18

3. Details of IC 89C5145

LIST OF FIGURES

NO.TITLE PAGE NO.

1.The organ of hearing5

2.Audiogram of normal ears and impaired ears11

3.Block diagram of

Embedded Microcontroller based Audiometry14

4.Basic building block of Linear Mode Power Supply17

5.Power Supply18

6.Function Generator21

7.Pre Amplifier Stage26

8.Power Amplifier30

9.BandPass Filter32

10.Frequency Response – BandPass Filter33

11.Clamper Circuit35

12.Clamping a Waveform36

13.Block diagram of

Successive Approximation A/D converter38

14.Illustration of conversion process41

15.Connection Diagram of ADC080442

INTRODUCTION

  1. INTRODUCTION

1.1. ABOUT THE PROJECT

There could be various disorders in the various parts of the ear. Audiological investigations help us to diagnose the nature of deafness and localize the site of disorder. The method by which patient's hearing sensitivity can be determined is termed as audiometry. It helps in assessing the nature, degree, and probable cause of the hearing impairment. In this technique, auditory stimuli with varying intensity levels are presented to the person who responds to these stimuli. The minimum intensity level of these stimuli to which consistent responses are obtained is taken as the threshold of hearing. Depending on this threshold, the patient’s hearing sensitivity can be estimated by obtaining an audiogram. An audiogram is a plot of threshold intensity versus frequency. Then the best-suited medical treatment or hearing aid or other assistive devices can be prescribed. There are different audiometric procedures depending on the stimuli used.

An audiometer is an instrument, which is used for carrying out these audiometric tests. The device would be portable, easy to use and can be used by a single person. This makes it ideal for demonstration purposes.

The functionality offered by the audiometer consists of automatic frequency and loudness selection that’s done during a typical test procedure. The user is only required to raise his or her hand when he or she hears a sound. This makes the product easy to use and user friendly. Once a test is complete, the results are displayed in the form of an audiogram that can be used to assess a person’s hearing ability. The basic functionality of the product was used to break it down to simple electronic components that could be designed to work together to create the complete system.

A summary of the detailed technical specifications is given below:

  • Test frequencies: 250Hz, 500Hz, 1000Hz, 2000Hz, 4000Hz and 8000Hz
  • Intensity: -20dB HL to 200dB HL
  • Input: Pure tone

A vital necessity of obtaining the most accurate results from the audiometer is achieved by performing the test in a location with little or no background noise. The type of environment is not easily possible in today’s rooms plagued with noise from electronic devices such as an air conditioner, fridge and a computer. To add more value to the product and making its results more reliable, the test must be conducted in a sound proof room. This reduces the background noise heard by the human ear. This feature makes the product more desirable, hence enhancing the overall system.

This report deals with the detailed electronic circuit diagrams and the practical application of the audiometer.

1.1.ORGANAIZATION PROFILE

Electronic Engineering Corporation is a leading Indian Manufacturer of a wide range ofbio-medical electronic instruments and scientific pumps.

With over a decade of experience and service to the scientific and medical profession, EEC's products are acknowledged for excellent performance and long-term reliability.

These medical and scientific instruments are used by reputed medical professionals and scientists in many clinics, hospitals government organizations, defense establishments, educational institutions and research laboratories. Rigid quality control and utmost care is exercised in the selection of materials that go into each instrument. All products are futurist in design and speciallybuilt to withstand rigorous use. Common features of these instruments are latest technology, high reliability components, compact design and simple operation.

The Registered Office and Factory details are as follows:-

Address

Electronic Engineering Corporation,
T-4, Dr.Vikram Sarabai Instronic Estate, Chennai – 600 041, Tamilnadu, India.

Telephone Numbers : 091 -044- 4925853
091-044- 4481680

Fax: 091-044-4925853

E-Mail:

Website:

PHYSIOLOGY

OF THE AUDITORY SYSTEM

  1. PHYSIOLOGY OF AUDITORY SYSTEM

Fig.1. The organ of hearing

The ear consists of three basic parts - the outer ear, the middle ear, and the inner ear. Each part of the ear serves a specific purpose in the task of detecting and interpreting sound. The outer ear serves to collect and channel sound to the middle ear. The middle ear serves to transform the energy of a sound wave into the internal vibrations of the bone structure of the middle ear and ultimately transform these vibrations into a compression wave in the inner ear. The inner ear serves to transform the energy of a compression wave within the inner ear fluid into nerve impulses which can be transmitted to the brain.

Generally, the lowest sound level that people of excellent hearing can discern has an acoustic sound power about 10-12 W, 0 dB

The loudest sound generally encountered is that of a jet aircraft with a sound power of 105 W, 170 dB.

2.1. CAUSES FOR HEARING LOSS

Each section of the ear has diseases specific to it and specific tests (investigations) are there to identify disorders in each portion. The common cause of disorder in the external auditory meatus is collection of either wax or fungal debris or foreign body in it. To diagnose this no investigation is required and your doctor can see it directly and clean it with instruments. This deafness due to blockage of the external ear is usually very slight.

The middle ear comprises of the eardrum, the ossicles, and the air space within the cavity of the middle ear. The common diseases affecting this portion are perforation in the ear drum, a stiffness or damage to the chain of small bones in the ear, and collection of fluid in the middle ear space (called middle ear effusion). A perforation can usually be diagnosed just by visualizing the ear-drum; however the other middle ear disorders require special investigations for confirmation.

The disease of the inner ear, i.e. the cochlea is difficult to treat. Disorders of the inner ear not only causes a deafness called sensorineural (perceptive) deafness but also may case a peculiar sensation of buzzing sounds in the ear called tinnitus. Deafness due to disorders of the inner ear is commonly refractory to medical and surgical methods and usually hearing aids are the only option. Deafness may also occur due to diseases of the nerve carrying the sensation from the cochlea to the brain. Deafness due to disorder of the nerve is called retrocochlear deafness and deafness due to disorders of the nerves which carry the sensation of hearing still higher up to auditory cortex are called central deafness.

The common symptoms of disorders in the auditory system are difficulty in hearing normal conversation from a distance of 8 feet or a whisper from a distance of 3 feet, can hear people talk but have difficulty in understanding what they say i.e. spoken word appear jumbled up, hear comparatively less in one ear, require to raise the volume of which is uncomfortable to other people, hear whistling/buzzing sounds in the ear or in the head when actually such sounds are not there, have a sensation of blockage/heaviness in one or both ears.

HEARING TESTS

3. HEARING TESTS

Hearing test helps to detect hearing loss, identify how severe it is, and determine what is causing it. It also measures the ability of sound to reach the brain. Sounds are actually vibrations of different frequencies and intensities in the air around us; air in the ear canals and bones in the ears and skull helps these vibrations to travel from the ear to the brain, where we "hear" them. By measuring our ability to hear sounds that reach the inner ear through the ear canal (air-conducted sounds) and sounds transmitted through bones (bone-conducted sounds), hearing tests helps us to determine what kind of hearing loss we have.

Most hearing tests require a response to a series of tones or words. These tests include:

  • Whispered speech testing, which is a simple screening test that assesses our ability to hear whispered speech across a short distance.
  • Pure tone audiometry, which measures our ability to hear sounds that reach the inner ear through the ear canal (air conduction). By using vibrations, this test can also measure hearing through bone (bone conduction).
  • Tuning fork testing, this assesses how well the sound moves through our ear.
  • Speech reception and word recognition testing, which measure our ability to hear and understand speech.

An ear examination may be done:

  • As part of a routine physical examination.
  • To screen infants and children for hearing loss.
  • To determine the cause of symptoms such as earache, a feeling of pressure or fullness in the ear, or hearing loss.
  • To detect excess wax or a foreign object in the ear canal.
  • To detect the location of an ear infection. The infection may involve only the external ear canal (otitis externa) or the middle ear behind the eardrum (otitis media or otitis media with effusion).
  • To monitor the effectiveness of treatment for an ear problem.

3.1. PURE TONE AIR CONDUCTION THRESHOLD TESTING

To assess sensitivity, a series of 0.5 s bursts of single-frequency stimuli are presented to the subject through calibrated earphones worn on the head. The subject is requested to respond (by hand raising or button pushing) each time a beep is heard, even if it is faint. Pure tone testing is performed separately for each ear and for frequencies from 250 to 8000 Hz. The audiometer attenuator is adjusted until the person responds correctly to 50% of the test beeps presented. The smallest increment step on the attenuator is usually 5 dB. The threshold (50% correct responses) is recorded on the audiogram using a (red) “o” for the right ear and a (blue) “x” for the left ear. The test signal passes through the outer ear, the middle ear, and the inner ear and is further processed by the central auditory system. Any hearing loss measured may be due to pathology of one or more parts of the ear.

3.2. REPRESENTATION OF SOUND

  • Sound is described in terms of frequency and intensity.
  • Frequency, or pitch (whether a sound is low or high), is measured in vibrations per second, or hertz (Hz). The frequencies of normal conversations in a quiet place are 500 to 2,000 Hz.
  • Intensity, or loudness, is measured in decibels (dB). The intensities of some common sounds are 15 to 25 dB for a whisper, 40 to 60 dB for background noise in the home or office, 100 to 120 dB for loud music, and 140 to 180 dB for a jet aero plane.

3.3. AUDIOGRAM

An audiogram is a plot of threshold intensity versus frequency. The intensity scale in HL increases downwards, and hence the audiogram resembles like an attenuation response, a lower point on the audiogram indicating higher loss. A typical audiogram (dB HL vs. frequency graph) comparing normal and impaired hearing is shown in Fig.2. The dip or notch at 4 kHz as shown, or at 6 kHz, is a symptom of noise-induced hearing loss.

Fig.2. Audiogram of normal ears and impaired ears

Most thresholds are approximately 0 dB HL for a normal ear. Points below 0 dB HL on the scale denote louder threshold levels, whereas those above, expressed in negative decibels with respect to the zero level, are less intense levels which, because of individual hearing differences, some people may normally hear. Four separate curves can be obtained - right ear air conduction (AC), right ear bone conduction (BC), left ear AC, and left ear BC. This comprises the audiogram.

The symbols used on most audiograms are

x - Left air conduction

o - Right air conduction

In normal individuals, a small discrepancy is often seen between air and bone conduction thresholds, the "AC-BC gap". At any given frequency the threshold for AC is somewhat lower than BC (i.e., a stronger signal is needed for BC).

The following table relates hearing thresholds (how loud a sound of certain frequency must be for a person to hear it) to the degree of hearing loss for adults.

Table.1. Relation between Hearing Thresholds and Degree of Hearing Loss (for adults)

Hearing Thresholds (in decibels, dB) / Degree of hearing loss / Ability to hear speech
0-25dB / None / No significant difficulty
26-40dB / Mild / Difficulty with faint or distant speech
41-55dB / Moderate / Difficulty with conversational speech
56-70dB / Moderate to severe / Speech must be loud; difficulty with group conversation
71-90dB / Severe / Difficulty with loud speech; understands only shouted or amplified speech
91+ dB / Profound / May not understand amplified speech

BLOCK

DIAGRAM

OF THE AUDIOMETER

4. BLOCK DIAGRAM

Fig.3. Block diagram of Embedded Microcontroller based Audiometry

4.1. BLOCK DIAGRAM DESCRIPTION

The block diagram for audiometer consists of

  • Function Generator
  • Pre Amplifier
  • Power Amplifier
  • Attenuator Control
  • Head Phone
  • Clamper Circuit
  • A/D Converter
  • Microcontroller-89C51
  • Liquid Crystal Display

The signals generated by the function generator are given to the pre-amplifier. The square wave is amplified and is given to the clamper circuit which in turn converts the square wave to positive going pulses. The pulses are given to the A/D Converter. In the meantime, the sine wave is amplified by the pre-amplifier and the output is given to power amplifier. The output of power amplifier is given to the attenuator control. The attenuator control allows only a certain band of frequencies to the Head Phone (which should be placed on the patient) and to A/D Converter. The output of ADC is given to the Microcontroller and finally the output is displayed with the help of Liquid Crystal Display.

HARDWARE

5. HARDWARE

5.1. POWER SUPPLY

All electronic circuits need dc power supply either from battery or power back units. It may not be economical and convenient to depend upon battery power supply. Hence, many electronic equipment contain circuits which convert the ac supply into dc voltage at the required level. The unit containing these circuits is called the Linear Mode Power Supply (LPS). In the absence of ac main supply the dc supply from battery can be converted into required ac voltage which may be used by computer and other electronic systems for their operation. Also, in certain applications dc to dc conversion is required. Such a power supply unit that converts dc into ac or dc is called Switched Mode Power Supply (SMPS).

  1. Linear Mode Power Supply: ac/dc power supply convertor
  2. Switched Mode Power Suppy:

a)dc/dc power supply convertor

b)dc/ac power supply convertor

5.1.1. Linear Mode Power Supply

An ac/dc power supply converts ac mains (230V, 50Hz) into required dc voltages (and is found in all mains operable system). The basic building blocks of the linear power supply are shown in figure.

Fig.4. Basic building block of Linear Mode Power Supply

A transformer supplies ac voltage at the required level. This bidirectional ac voltage is converted into an unidirectional pulsating dc using a rectifier. The unwanted ripple contents of this pulsating dc are removed by a filter to get dc voltage. The output of the filter is fed to a regulator which gives a steady dc output independent of load variations and input supply fluctuations.

Fig.5. Power Supply

This circuit can give

Table.2. Relation between regulator names and its output voltages

Name / Voltage
LM7809 / + 9 volts
LM7905 / - 5 volts
LM7909 / - 9 volts

5.2. FUNCTION GENERATOR

A function generator is an instrument that generates signals for use in electronic test situations.

  • A function generator generates signals. We may also find that another common name for the instrument is signal generator.
  • The signals produced by a function generator can have many waveshapes. We may find
  • Sinusoidal signals
  • Square wave signals
  • Triangle signals
  • Ramp signals
  • Pulses
  • Noise signals
  • User-defined signals
  • The frequency of the signals can be controlled.
  • The amplitude of the signals can be controlled.

Not all of the signals above are found on every function generator, and there are more specialized functions that can be performed. In general, a generator that produces the first three signals may be called a signal generator, and with more functions the generator may be called a function generator.