EMBEDDED MICROCONTROLLER BASED SYSTEM FOR MEASUREMENT OF NEURO SENSORY HEARING LOSS

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2 Νοε 2013 (πριν από 4 χρόνια και 6 μέρες)

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EMBEDDED MICROCONTROLLER

BASED SYSTEM

FOR

MEASUREMENT OF NEURO
SENSORY HEARING LOSS





ABSTRACT




ABSTRACT





Audiometry is the technique to identify & 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.


INTRODUCTION


INTRODUCTION



Accurate assessment of hearing is vital to the diagnostic
evaluation of patients with suspected otology disorders
for the determination of the underlying process, as well as
in the planning of rehabilitation of hearing loss.





An
audiometer essentially consists of a function
generator, a stereo amplifier stage, an ear phone and a
masking unit.




The embedded microcontroller based system is more
precise than the conventionally used audiometer.


PHYSIOLOGY OF THE


AUDITORY SYSTEM

PHYSIOLOGY OF AUDITORY SYSTEM

THE ORGAN OF HEARING


Parts of the Ear



Outer Ear:



It
serves to collect and channel sound to the middle ear.


Middle Ear:



It 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.


Inner Ear:



It serves to transform the energy of a compression wave
within the inner ear fluid into nerve impulses which can
be transmitted to the brain.



TESTING CARRIED

IN HUMAN EAR


TESTING CARRIED IN HUMAN EAR


Pure tone air conduction threshold testing


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.



This 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 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.



Any hearing loss measured may be due to pathology of
one or more parts of the ear.


Audiogram

BLOCK DIAGRAM

OF AUDIOMETER

FUNCTION

GENERATOR

PRE

AMPLIFIER

POWER

AMPLIFIER

ATTENUATOR

CONTROL

A/D

CONVERTER

CLAMPER

HEADPHONE

ON

PATIENT

PATIENT

RESPONSE

SWITCH

LCD DISPLAY

-
20DB TO 200DB

HEARING LEVEL

MICRO CONTROLLER

89C51

OPERATOR

SWITCH

PRE

AMPLIFIER

POWER

AMPLIFIER

HARDWARE


POWER SUPPLY


POWER

SUPPLY


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




LINEAR MODE POWER SUPPLY


OPERATION

OF

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
.


POWER SUPPLY


CIRCUIT DIAGRAM

FUNCTION
GENERATOR


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

signal

produced

by

the

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
.







There

are

three

basic

controls

on

a

function

generator
.


They

are
:



A

control

to

set

frequency



A

control

to

set

waveshape

(sinusoid,

triangle,

square)



A

control

to

set

amplitude




The function generator can be used to do the following
adjustments:


To set the frequency to a value by using a pot.


To set the amplitude to a value by using another pot.


To change the wave shape with the help of a rotary
switch.


PRE
-
AMPLIFIER


PRE

AMPLIFIER




An

amplifier

which

amplifies

the

input

without

producing

any

phase

shift

between

input

and

output

is

called

non
-
inverting

amplifier
.




The

input

is

applied

to

the

non
-
inverting

input

terminal

of

the

op
-
amp
.





The

op
-
amp

always

amplifies

the

difference

input

voltage

Vd
.





This

difference

voltage

is

the

difference

between

the

voltages

Vin

and

Vf

where

Vf

is

the

feedback

voltage
.






The

feedback

voltage

opposes

the

input

voltage

that

is,

it

is

180
°

out

of

phase

with

respect

to

the

input
.

This

indicates

that

the

feedback

is

negative
.



When the input signal and part of the output signal are in
phase, the feedback is called positive feedback. Use of
positive feedback results in oscillations and hence not
used
.


PRE AMPLIFIER


CIRCUIT DIAGRAM

POWER AMPLIFIER

POWER AMPLIFIER


CIRCUIT DIAGRAM



In general, an amplifier receives an input signal from
some transducer or other input source and provides a
large amplified signal to some output device or another
amplifier stage.



The small signal amplifiers are basically voltage
amplifiers, the voltage and current signal levels are small
in such amplifiers.




The output current capability of such amplifier is limited.
The amount of power handling capacity and power
efficiency are of little concern for the small signal
amplifiers.




The output current capability of such amplifier is limited.




The amount of power handling capacity and power
efficiency are of little concern for the small signal
amplifiers




The power amplifier is basically used to amplify an audio
signal faithfully.




The loads to such amplifiers are generally loud speakers,
headphones and servomotors



ATTENUATOR
CONTROL


ATTENUATOR CONTROL



The attenuator control acts as a band pass filter.




A band pass filter is basically a frequency selector.



It allows one particular band of frequencies to pass.



Thus, the pass band is between the two cut
-
off
frequencies fH and fL where fH>fL.




Any frequency outside this band gets attenuated.


ATTENUATOR CONTROL


CIRCUIT DIAGRAM

CLAMPER

CIRCUIT


CLAMPER

CIRCUIT



Clamper

is

a

circuit

that

"clamps"

a

signal

to

a

different

dc

level
.



The

different

types

of

clampers

are

positive

negative

and

biased

clampers
.




A

clamping

network

must

have

a

capacitor,

a

diode

and

a

resistive

element
.




The

magnitude

R

and

C

must

be

chosen

such

that

the

time

constant

RC

is

large

enough

to

ensure

that

the

voltage

across

the

capacitor

does

not

discharge

significantly

during

the

interval

the

diode

is

non
-

conducting
.


CLAMPER CIRCUIT DIAGRAM

ANALOG

TO DIGITAL
CONVERTER



ADC



Analog

to

digital

converter

are

classified

into

two

general

groups

based

on

the

conversion

techniques



One

technique

involves

comparing

a

given

analog

signal

with

the

internally

generated

reference

voltages
.




This

group

includes

successive

approximation,

flash,

delta

modulated

(DM),

adaptive

delta

modulated

and

flash

type

converters
.





Another

technique

involves

changing

an

analog

signal

into

time

or

frequency

and

comparing

these

new

parameters

against

known

values
.




This

group

includes

integrator

converters

and

voltage
-
to
-
frequency

converters
.



SUCCESSIVE APPROXIMATION ADC


SOFTWARE

INTRODUCTION TO
EMBEDDED SYSTEM


INTRODUCTION

TO

EMBEDDED

SYSTEM



Microprocessors

and

microcontrollers

are

widely

used

in

embedded

system

products
.

An

embedded

product

uses

a

microprocessor

or

microcontroller

to

do

one

and

task

only
.




A

printer

is

an

example

of

embedded

system

since

the

processor

inside

it

performs

one

task

only

;

namely,

getting

the

data

and

printing

it
.




In

embedded

system,

there

is

only

one

application

software

that

is

typically

built

in

ROM
.



IC

89
C
51

MICROCONTROLLER



The

AT
89
C
51

is

a

low
-
power,

high
-
performance

CMOS

8
-
bit

Microcomputer

with

4

Kbytes

of

Flash

Programmable

and

Erasable

Read

Only

Memory(PEROM)
.



The

on
-
chip

Flash

allows

the

program

memory

to

be

reprogrammed

in
-
system

or

by

a

conventional

nonvolatile

memory

programmer
.



It

is

a

powerful

microcomputer

which

provides

a

highly

flexible

and

cost

effective

solution

to

many

embedded

control

applications
.


ROM



4k



RAM



128



I/O Pins



32



Timer



2



Interrupt



6



Vcc



5V


Packaging


40


Details of IC89C51

CONCLUSION

CONCLUSION




Thus the Embedded Microcontroller Based
Audiometer is used to determine the sensitivity of the human
ear. Accurate assessment of the hearing loss can be done using
this device.



The conventional audiometer is analog in nature. In this
project the embedded micro
-
controller concepts are
implemented to make audiometery more versatile, cost
effective and simpler in design.




In future, we can enhance the system by having
additional graphic features, data storage and signal processing
advantage of a PC based system, with the added benefit of
economy and portability.

The Kit designed by us