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 SYSTEMTHE 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

FUNCTIONGENERATOR

PRE AMPLIFIER

POWERAMPLIFIER

ATTENUATORCONTROL

A/D CONVERTERCLAMPER

HEADPHONEON

PATIENT

PATIENTRESPONSE

SWITCH

LCD DISPLAY-20DB TO 200DB

HEARING LEVEL

MICRO CONTROLLER89C51

OPERATORSWITCH

PRE AMPLIFIER

POWERAMPLIFIER

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 convertorb)      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.

N1N2

N3

1N4007

10

u

10

u

10

u

10

u

10

u

10

u

10

u

10

u

7809 7805

7909

230 VAC

5 V9 V

-9 V

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.

100k

10u

22k

200n

22

k

100k

10u

22k

200n

22

k

10

n

200n-

+ +

LM324/NS -

+ +

LM324/NS

FromBuffer

To PowerAmplifier

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.

-

+ +

!OPAMP

470k

10n 10n

10n 6

8k

InputOutput

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

10u 1k

D1

1N

400

7 10kInput Output

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 89C51 MICROCONTROLLER

The AT89C51 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