Pure tone audiometer design

Abstract

Audiometry ia a technique which is used to measure where the hearing deficit stems from in aural way and whwt the degree of severity of deficit is. This thesis work basically focused on a prototype of pure tone audiometer generating pure tone, wide and narrow band noise and warble tone. Direct Digital Synthesis (DDS) and logarithmic shaping methods are utilized for sine wave generation. For noise, firstly wide band noise is generated and then it is filtered by switched capacitor filter for narrow band noise. Warble tone is frequency modulated signal. Frequency modulation is implemented by Voltage Controlled Oscillator. All the obtained signals are made suitable to ouyput appratus and opening (80 dB) level via Digitally Controlled Potentiometer (DCP). Desired signal is selected via the multiplexer for right or left channel. Sequentially in order to match the signal between the -10 dB and 100 dB, its volume is readjusted in a special functional unit. Ultimately to supply the desired current drive for the TDH39 and bone vibrator, a current feedback operational amplifier is used. All the functional units are managed with the microcontroller coded as MSP430FG439 and the status of the device is showed on Liquid Crystal Display (LCD). In Turkey, audiometer is not manufactured. Despite the fact that this prototype of audiometer is not appropriate to come on the market, it may give idea for production of more complex ones. Moreover, because of the fact that many hearing testing devices have analogous units with this protype, inspecting this work carefully may give useful ideas about implementation of those devices. This protype is tried to work out based on the standard of TS 9595-1-4 (EN60645-1-4) of Turkish Standards Institution.|Keywords: Pure tone audiometer, MSP430, DDS, Warble tone, Narrow band noise.