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ELECTRONIC STETHOSCOPE ARRAY Groupe 70 Robin GUIGNY & Fatima Zohra HASNAOUI ECE 445 Spring 2016
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INTRODUCTION 2/5 medical misdiagnosis & underdiagnosis per year Traditional stethoscopes only provide qualitative diagnosis Find a way to provide a more accurate diagnosis
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Objectives Have a quantitative assessment of lung activity Capturing and processing the lung signal to identify symptoms Easy-to-read output for the doctor
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Overall System Patient Sound capture&treatment Signal analysis and diagnosis
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Table of contents 1.Block diagram 2.Microphone 3.Filter 4. Bluetooth module 5 Headphone amplifier 6. Power supply 7. Software
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Block diagram
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Choosing the microphone Sensitivity and frequency response Cost Interferences Power
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Microphones comparison MEMSCondenserFiber optic Sensitivity & freq response >100Hz Cost$400 Interferences Power Acceptable Very bad Good Final choice!
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Choosing the filter High attenuation in the stopbands Flat passband Easy design for multiple modifications Requirements: Attenuation < 6 dB in the passband [50Hz ; 2500 Hz] Attenuation > 12 dB in [0 - 30 Hz] and 6000Hz +
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Filter design Butterworth filter : maximally flat in the passband. 3rd order : to obtain desired attenuation in the stopband. Sallen-Key design : easy to implement and modify.
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Identification Butterworth 2 nd cutoff frequency : f=2500Hz Q=1/√2
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Schematics
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LTSpice Bode diagram
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Results
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Attenuation < 6dB passband Vs/Ve > 1/2 at 2500 Hz and at 50Hz ✔
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Attenuation > 12dB Vs/Ve < 1/4 for 6000Hz+ and [0 – 30 Hz] ✔
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Bluetooth module choice Analog input Resolution > 8 bits
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Numato’s GPIO BT Module 10 bits resolution 3,3V ADC range RN-42 2.4GHz Bluetooth module Command through HyperTerminal
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Headphone amplifier design Able to drive low-impedance output found in headphones (9Ω to hundreds of Ω). Provide >0,5mW to 9Ω earphones (96dBSPL/mW) for the loudest expected sound. This corresponds to 67mV output. Requirement
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Cmoy audio amplifier
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Results ≈70mV Pk-Pk for loudest sound ->93dBSPL : tolerated for 8 hours X100 amplification
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Power unit Relatively small in-use time (estimated <30 min/day) No particular need for rechargeable battery. Able to provide +/-9V to all the opamps Requirement The battery must allow 10 hours of use (last about a month)
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Power supply schematics
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Battery life 2 x 9V alkaline batteries + 3V coin cell battery Battery life calculation : LT082 opamps : 2,5mA Absolute max for BT module : 95mA
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Software overview Aim : visualize lung sounds and spot symptoms How? According to lung sounds features (FFT, shape, length) Two main abnormal sounds are linked to lung diseases: Wheezes Crackles Fine crackles Coarse crackles
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Lung sounds features SoundsMax peak frequencyWaveformDuration Normal200Hz Breath in = Cycle*2/3 Breath in = breath out + 11dB 2s<cycle length<10S Wheezes400HzSinusoid>80 ms Fine Crackle650HzDampened wave deflectionAround 5ms Coarse Crackle350HzDampened wave deflectionAround 15 ms Focus of the software
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Steps Pick the soundPress a buttonCompute fft Find max peak’s frequency (f>200Hz) Conclusion
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Flowchart
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User interface Scroll bar
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Example
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Requirements Latency : 2 to 10 s 95% success
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Verifications Latency : ok ✓ 95% success rate : ok on lung sounds files provided by medical research articles -> need for a bigger sample
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Issues Bluetooth : not able to connect the bluetooth module Analog identification can be possibly implemented if we take into account localization : A) Fine crackles B) Wheezes C) Coarse crackles Lung sound preferential spots
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Conclusion Hardware Software Link between the two?
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Further work Bluetooth transmission between hardware and software Add microphones (multiple inputs) Take microphone localization into account Try with other type of filters (FIR..) Design stethoscope head for better acoustic clarity
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Thank You!
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