The Design and Construction of the Hearing Aid Device

The Design and Construction of the Hearing Aid Device

Chapter One

AIM AND OBJECTIVES

This project aims to design and construct a hearing aid and, the objectives are as follows:

To design a hearing aid
To construction of the designed hearing aid and
To test the constructed device

CHAPTER TWO

LITERATURE REVIEW

REVIEW OF PREVIOUS WORK ON DESIGN OF HEARING AID

Schum,(2004)) designed and constructed a low-cost hearing aid to produce an amplified sound for people with hearing loss. A 9V dc was used as the power supply. The condenser microphone was used as input transducer to pick up sound from the environment for conversion to electrical signal, NPN transistor (BC548C) along with three capacitors and five resistors were used as pre-amplifier.to amplify. The integrated circuit (IC) TDA2822M, available in 8-pin mini chip package and specially designed for portable power amplification was used for the amplification function. A 32 ohms ear phone was used as the output transducer to convert the amplified electrical signals back to sound. Also, Levitt (1986) worked on A Digital Master hearing aid. They used computer simulation in evaluating conventional and experimental hearing aids. Two illustrative examples are provided. The first involves the simulation of a convention of a master hearing aid and its application in evaluating different adaptive strategies in the prescriptive fitting of hearing aids. The second example involves the simulation of the hearing aid embodying modern digital signal-processing techniques for the reduction of background noise. A high-speed array processor is used in order to accomplish these simulations in real time.

Yusuf,(2013) designed and constructed a Hearing Aid Device. In their work they used TDA 2822M IC configured to produce an audio amplification which is converted to audio signal through a headphone. Design equations were employed to calculate the physical parameters of the circuit. They employed bridge type amplifier for their amplification.After the design, the circuit was constructed and tested on 5 people with partial hearing problem. The result showed that there was a significant improvement in the hearing ability of all the patients tested. Recommendations were proposed for further improvement.

The design of hearing aid carried out in this work will employ stereo type amplification method using commonly available components so as to make it cost effective.

HISTORY OF HEARING AID DEVICE

The first hearing aid was created in the 17^th century. The movement toward modern hearing aids began with the creation of the telephone, and first electric hearing aid was created in 1898. (Howard and Alexander., 1998) By the late 20^th century, the digital hearing aid was distributed to the public commercially. Some of the first hearing aids were external hearing aids. External hearing aids which directed sounds in front of the ear would fit behind or in the ear.

The first electric hearing aids were constructed after the invention of the telephone and microphone in the 1870s and 1880s. The technology within the telephone increased how acoustic signal could be altered. Telephones were able to control the loudness, frequency, and distortion of sounds. These abilities were used in the creation of the hearing aid. The first electric hearing aid, called the Akouphone, was created by Miller Reese Hutchison in (1898). It used a carbon transmitter, so that the hearing aid could be portable. (Wikipedia.org)

The development of transistors in 1948 by bell laboratories led to major improvements in the hearing aid design. The transistor was invented by John Bardeen, Walter Brattain, and William Shockley. Transistors were created to replace vacuum tubes: they were small, required less battery power and had less distortion and heat than their predecessor. These vacuum tubes were typically hot and fragile, so the transistor was the ideal replacement.

HEARING IMPAIRMENT OR HEARING LOSS

Hearing loss may occur in one or both ears. In children hearing problems can affect the ability to learn spoken language and in adults it can cause work related difficulties. Causes of hearing loss include.

Earwax
Infection
Disease
Circulatory problems
Trauma, noise exposure
Toxic medications, and
Heredity or hereditary weakness.

CHAPTER THREE

MATERIALS AND METHOD

MATERIALS

The materials used in the design of the unit mentioned above includes

5V DC battery
Diode
Condenser Microphone
Capacitors
Resistors
Transistor
TDA2822M Integrated circuit
Switch
Ear phone

METHOD

1.5V DC battery, Diode, condenser Microphone, Capacitors, Resistors, Transistor, TDA2822M Integrated circuit, Switch, and Ear phone were used in designed and constructed of the hearing aid device. The condenser microphone was used as input transducer to pick up sound from the environment to converted the pick up sound signal in to electrical signal, the NPN transistor (BC548C) was used as a pre-amplifier in order saved as an amplifying the signal device, the integrated circuit (IC) TDA2822M, available in 8-pin mini chip package which is the heart of the circuit were specially designed for portable power amplification function. A 32 ohms ear phone Was used as the output transducer to convert the amplified electrical signals back to sound.

Also this work is done by designing the following units.

Power supply unit
Design analysis of input transducer
Pre-amplifier stage
Medium power amplifier stage

POWER SUPLY UNIT

The entire circuit of hearing aid device designed in this project work consumes a very small amount of power within the range of 10 mill watts. Furthermore, the voltageRequirement of every major component is within the range of 1.8 volts and 15 volts. Therefore, for portability, a 1.5V DC battery is used to power the circuit.

CHAPTER FOUR

RESULT AND DISCISSION

RESULT

Result of Test of Amplifier Gain against Frequency

The result of the test on the frequency response of the amplifier is tabulated in Table 1 and plotted in as shown in fig 4.3

CHAPTER FIVE

SUMMARY, CONCLUSION AND RECOMMENDATIONS

SUMMARY OF THE WORK

This research on the design and construction of a hearing aid device was designed based on different methods which include Stereo and Bridge amplifiers methods. The units that made up the hearing aid device were designed based on theoretical calculations. The designed units were the constructed and cased. The result of the frequency response shows that the frequency response of the stereo design is 10 KHz. This shows that it has low frequency response compared to bridge with 20 KHz. The bridge type though more efficient with respect to clarity of sound was discovered to consume more power. It also required more components thereby making it more expensive than stereo hearing aid. Hence both methods can be utilized in the design of hearing aid. But the stereo time is recommended due to its low power consumption and low cost. However, the aim of the project was achieved.

CONCLUSION

The aim of this work was to design a hearing aid system that pre-amplifies an acoustic signal Picked up by a condenser microphone; the pre-amplified signal is then further amplified before being converted to sound by another transducer (speaker). The designed and constructed circuit was tested on different set of people with different degree of hearing problem. The final test showed that the device could prove very useful for people with partial hearing problems. However, the device had no impact on persons suffering from complete deepness.

RECOMMENDATIONS

For further improvement, it is recommended that a wireless hearing aid device should be designed and constructed to reduce the weight. The casing of the hearing aid should be made up of more portable, qualitative and lighter plastic material so as to reduce the overall weight and size. During the design, more care should be taken so as to avoid feedback signal between the microphone and the headphone which may result in noisy signal.

REFERENCES

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(American Speech-Language-Hearing Association [ASHA], 2005), ’’ www.ASHa.int/en/’’
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