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 CONVERTER
CLAMPERHEADPHONE
ONPATIENT
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 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.
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
68
k
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
40
07
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