Design And Construction Of A Hearing Aid

ABSTRACT

This work is on a hearing aid. A hearing aid is a device designed to improve hearing. Hearing aids are classified as medical devices in most countries, and regulated by the respective regulations. Hearing aids are the best option for correcting hearing loss and resuming a high quality of life. Hearing aids contain at least one microphone to pick up sound, a computer chip that amplifies and processes sound, a speaker that sends the signal to your ear and a battery for power. Hearing aids are incapable of truly correcting a hearing loss; they are an aid to make sounds more accessible.

TABLE OF CONTENTS

COVER PAGE

TITLE PAGE

APPROVAL PAGE

DEDICATION

ACKNOWELDGEMENT

ABSTRACT

CHAPTER ONE

• INTRODUCTION
• BACKGROUND OF THE PROJECT
• OBJECTIVE OF THE STUDY
• SIGNIFICANCE OF THE STUDY
• SCOPE OF THE PROJECT
• APPLICATION OF THE PROJECT
• METHODOLOGY
• PROJECT ORGANISATION

CHAPTER TWO

LITERATURE REVIEW

• OVERVIEW OF THE STUDY
• USES OF THE STUDY
• REVIEW OF CANDIDACY AND ACQUISITION OF THE STUDY
• REVIEW OF DIFFERENT TYPES OF HEARING AID
• HISTORICAL BACKGROUND OF HEARING AIDS

CHAPTER THREE

METHODOLOGY

• BASICS OF THE SYSTEM
• SYSTEM BLOCK DIAGRAM
• POWER SUPPLY UNIT
• DESIGN ANALYSIS OF INPUT TRANSDUCER
• PRE-AMPLIFIER DESIGN
• MEDIUM POWER AMPLIFIER STAGE
• RC DECOUPLING UNIT
• OUTPUT UNIT
• MATERIALS USED AND CONSTRUCTION

CHAPTER FOUR

TEST AND RESULT ANALYSIS

• CONSTRUCTION PROCEDURE
• ASSEMBLING OF SECTIONS
• PACKAGING
• TESTS
• RESULTS

CHAPTER FIVE

• DISCUSSION
• CONCLUSION
• RECOMMENDATION
• REFERENCES

CHAPTER ONE

1.0                                                       INTRODUCTION

An electronic hearing aid is a small device placed in or around the ear to improve the hearing of those with hearing loss. The basic components of a hearing aid are a microphone, signal conditioning, a receiver also known as a speaker, and a battery. The microphone converts the sound into an electric signal. The signal then undergoes conditioning that can be as simple as amplifying all of the sound equally, to more advanced equalization involving a digital signal processor. The receiver converts the electronic signal back to sound, and the battery powers the electronics (Schum, D.J. 2004).

There are four main styles of hearing aids on the market today. From largest to smallest, they are behind the ear (BTE), in the ear (ITE), in the canal (ITC), and completely in the canal (CIC). The BTE style sits behind the ear with a clear tube going to an earmold in the ear to deliver the sound. A variation on this style is called an open-fit-behind-the-ear (OTE) where the earmold is replaced by a small tip, resulting in a more open feeling. Other variations include replacing the tube with wires and moving the receiver from the behind the ear to inside the ear. The ITE style moves the hearing aid into the outer ear, where it becomes a single unit with the earmold. This style fills up most of the outer ear and appears as a solid mass. The ITC style moves some of the hearing aid into the ear canal and reduces the space taken up in the outer ear, but is still plainly visible. The CIC style is the smallest of them all, as it fits completely inside the ear canal, thus nearly disappearing from view.

There are many features available for today’s hearing aids, including volume control, remote control, telecoil, direct audio input, FM reception, Bluetoothcapabilities, directional microphone, compression, clipping, frequency shifting, wind-noise management, data logging, self-learning, moisture resistance, and earmold venting. Some of these features require external area to implement and become more difficult to include as the size of hearing aids shrinks, while other features can be implemented in all hearing aids.

Volume control is performed manually with buttons or a rotary dial on the hearing aid. A remote control eliminates the need for buttons and dials on the hearing aid and can be used to control all the features of the hearing aid. A telecoil is an alternate input other than the microphone, and it originally picked up the magnetic signal generated by older telephones with speakers driven by magnetic coils so that listeners could hear better when talking on the telephone. Today’s telephones and other alternate listening devices build-in this capability in order to work with a telecoil and specifically indicate that they are hearing aid compatible. Direct audio input and FM reception are other ways to input sound or speech into the hearing aid, the first using a wired connector as an input, and the other an FM radio receiver. An emerging trend is to include Bluetooth capability to receive sound from a cell phone or music player. The Bluetooth device can either be integral to the hearing aid or an add-on device through the telecoil or FM input (Schum, D.J. 2004).

A hearing aid with directional microphones uses two or more microphones to receive sound from multiple directions. This improves the signal-to-noise ratio (SNR) of speech when heard in a noisy environment, and enhances the quality of speech further when used with digital signal processing. Compression and clipping both increase listening comfort by reducing portions of the sound that are too loud but, in some cases, just clip or limit the sound. Frequency shifting uses digital signal processing to shift speech to a lower frequency, which is helpful for people with high-frequency hearing loss. Wind-noise management detects wind and eliminates the feedback that would otherwise cause ringing sounds to be heard by the hearing aid wearer (Paul, S. 2000).

Data logging records the listening environment and how the hearing aid is used. A hearing professional can use this information to fine-tune hearing aid performance. Self-learning uses the data logs and fine-tunes the performance on its own over time. Moisture resistance helps reduce repairs due to exposure to moisture, and earmold vents provide additional comfort by reducing the closed-in sensation felt when wearing an earmold type of hearing aid (Schum, D.J. 2004).

1.1                                            BACKGROUND TO THE STUDY

Hearing is one of the five senses along with vision, taste, smell and touch. The ear serves asa receiver of incoming sounds. Although the ear receives sound and is the sense organ for hearing, it is the brain and central nervous system that interpret the sound. The human auditory system can generally hear sounds within the frequency range of 20 Hz and 20 kHz but the frequency range between 100Hz and 6 kHz contains most of the information of human voice (Sergei Kochkin, 2015). Although the sensation of hearing requires an intact and functioning auditory portion of the central nervous system as well as working ear, human deafness (extreme insensitivity to sound) and hearing loss most commonly occur because of damages of the ear, rather than the central auditory system.

Hearing aid device is a small electronic gadget that is fit in or behind the ear to improve one’s hearing and consequently communication ability (J., Moore, Brian C., 2007). While some people are born with hearing problem some others develop it as they grow. This problem can occur as a result of disease, aging, and injury from noise or intake of certain medicines (J., Moore, Brian C., 2007). Hearing problems could be that of complete deafness or partially impaired type. Hearing problem could occur after a person learned to talk (post lingual) or those with trilingual deafness that is, deafness that occurs before a person learns to talk. Deafness, whatever the degree or course, is generally a source of worry and frustration to the patient concerned as it affects almost all aspects of one’s life.

Hearing loss is usually reserved for people who have relative insensitivity to sound in the speech Frequency range. A hearing loss can happen when any part of the auditory system is not working in the usual way (J., Moore, Brian C., 2007)

The design and constructed hearing aid device can improve the quality of sound for people with hearing loss. The heart of the circuit is an integrated circuit which amplifies all the signals picked by the condenser microphone and converts them back into sound and sent to the ear. It is a battery-powered electronic device that can amplify sound for people with hearing loss. The amplification function of the hearing aid is made possible with several components; a microphone (input transducer) which picks up sound an amplifier which increases the volume or the sound, a receiver (output transducer) which changes the electrical signal back into sound and sends it to the ear (Schum, D.J. 2004).

Hearing aids have been available in four styles: body, eyeglass, behind-the-ear (BTE), and in-the-ear (ITE) hearing aid. Included in the category of ITE hearing aids are in-the- canal (ITC) and completely-in-the-canal (CIC) styles. While body and eyeglass style hearing aids were regularly used 40-50 years ago, they comprise only about 1% of all hearing aids marketed today. Instead, most individuals choose ITE (approximately 80%) or BTE (approximately 20%) style hearing aids. This transition in style, use, and preference is occurring for a number of reasons, including the reduction in the size of the components, durability, and cosmetic concerns on the part of the consumer (Theradja, B.L., 2003).

1.2                                    OBJECTIVE OF THE PROJECT

The objective of this work is to design an electroacoustic device which amplify sound for the wearer, usually with the aim of making speech more intelligible, and to correct impaired hearing as measured by audiometry. Hearing aids are considered medical devices. Ordinary small audio amplifiers or other plain sound reinforcing systems cannot be sold as “hearing aids”.

1.3                                   SIGNIFICANCE OF THE PROJECT

Hearing aids are incapable of truly correcting a hearing loss; they are an aid to make sounds more accessible. Two primary issues minimize the effectiveness of hearing aids:

When the primary auditory cortex does not receive regular stimulation, this part of the brain loses cells which process sound. Cell loss increases as the degree of hearing loss increases.

Damage to the hair cells of the inner ear results in sensorineural hearing loss, which affects the ability to discriminate between sounds. This often manifests as a decreased ability to understand speech, and simply amplifying speech (as a hearing aid does) is often insufficient to improve speech perception.

1.4                                   SCOPE OF THE PROJECT

Hearing aid to help people who have hearing loss. This hearing aid device circuit works using four transistors and several passive electronic components. Hearing Aids Central offers the best variety of digital in ear and behind the ear of basic parts as shown in the following diagram: A tone control circuit for a transistorized hearing aid.

1.5                                                                                          LIMITATION OF THE PROJECT

Some hearing aid comes with non-replaceable battery which can only be dispose when the battery dies, this means that hearing aid with non-replaceable battery can be costly than the one that has replaceable battery because if the battery dies one have to dispose it. Hearing aid can be noisy when the battery gets low.

1.6                                    APPLICATION OF THE PROJECT

These hearing aids are designed for medical practitioners with hearing loss who use stethoscopes. The hearing aid is built into the speaker of the stethoscope, which amplifies the sound. Hearing aid can also be used by aged people or people suffering from problem to improve their hearing.

1.7                                         METHODOLOGY

To achieve the aim and objectives of this work, the following are the steps involved:

1. Study of the previous work on the project so as to improve it efficiency.
2. Draw a block diagram.

• Test for continuity of components and devices,

1. Design and calculation for the device was carried out.
2. Studying of various component used in circuit.
3. Construction of the circuit was carried out.

• Finally, the whole device was cased and final test was carried out.

1.8                                PROJECT WORK ORGANISATION

The various stages involved in the development of this project have been properly put into five chapters to enhance comprehensive and concise reading. In this project thesis, the project is organized sequentially as follows:

Chapter one of this work is on the introduction to this work. In this chapter, the background, significance, objective limitation and problem of this work were discussed.

Chapter two is on literature review of this work. In this chapter, all the literature pertaining to this work was reviewed.

Chapter three is on design methodology. In this chapter all the method involved during the design and construction were discussed.

Chapter four is on testing analysis. All testing that result accurate functionality was analyzed.

Chapter five is on conclusion, recommendation and references.