Design and Analysis Study for a Cost Effective and/or Better Quality Hearing Aid Device

Abstract

World Health Organization report (2012) shows that 360 million people are suffering from disabling hearing loss worldwide. Hearing loss affects the developing and learning processes in children, while in adults, it affects and creates problems in the education, employment and general wellbeing. Hearing aid is the solution to it but a large number of hearing impaired people in Pakistan, either cannot afford the high prices of digital hearing aids, or they do not know how to choose a better quality hearing aid which suits their requirements. Moreover, since the analog hearing aids amplify the speech and noise signals equally, they are not much flexible and also have functional limitations. This research work is focused to primarily assist the hearing impaired people to choose better quality hearing aid devices keeping in view their budget. The research work also includes analysis, design and testing of a cost effective digital hearing aid. More than hundred digital hearing aids from different brands have been studied and comparatively analyzed. For user/patient, a selection procedure has been proposed in order to choose a better quality device keeping in view his/her budget/ hearing profile. Following the above objective, a microcontroller based cost effective, flexible, portable and small sized digital hearing aid has been designed and tested. The main components of the proposed system are sound detection circuit, a microcontroller and a digital to analog (DAC) converter. Audio signal from the microphone is amplified and converted to digital signal by 10 bit built-in analog to digital converter (ADC) of AVR atmega32 microcontroller and after the desired processing, the 8 bit DAC converts the signal back to analog signal and feed it to earphone. The internal clock of the microcontroller and built-in ADC avoids the extra circuitry and the external DAC helps in suppressing the low intensity background noise. The device is aimed to process the human voice frequencies only. It is tested in lab, implemented on PCB and it shows satisfactory results for the low frequency signals up to 3.5 kHz, which caters for the frequency range of most human voices. The minimum power (gain) of the device is 40 dB and has an adjustable gain of up to 80 dB. Based on the power range, this device is comparable to most of the lower cost digital hearing aids (mentioned in chapter 3) and the goal is to match it with Lotus Pro M device. Thus in future, the system will be developed for more effective noise suppression and broader frequency range, by adding frequency channels.