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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
CLAMPER
OPERATOR
SWITCH
POWER
AMPLIFIER
A/D
CONVERTER
MICRO CONTROLLER
89C51
LCD DISPLAY
-20DB TO 200DB
HEARING LEVEL
ATTENUATOR
CONTROL
HEADPHONE
ON
PATIENT
PATIENT
RESPONSE
SWITCH
HARDWARE
POWER SUPPLY
POWER SUPPLY
1.
2.
Linear Mode Power Supply:
ac/dc power supply convertor
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-tofrequency 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 89C51 MICROCONTROLLER
 The AT89C51 is a low-power, high-performance CMOS 8bit 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.
Details of IC89C51
ROM
4k
RAM
128
I/O Pins
32
Timer
2
Interrupt
6
Vcc
5V
Packaging
40
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