DHA Directional Hearing Aid

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DHA Directional Hearing Aid

• Team Members
• Noah Van Fossan
• Shareen Hossain
• Deepthi Chandra
• Christina Clemenz
• Laura Hanley
• Advisors
• Prof. Mark Bell
• Prof. Carla Zoltowski
• Project Partner
• Prof. Robert Novak

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DHA Directional Hearing Aid
Project Goal
To design and develop an inexpensive hearing aid
that will cancel out background noise so that a
person with a hearing impairment can carry out a
conversation in a noisy environment.
Overview
Four microphones forming a linear array are
embedded on an eyeglass frame and connected to a
circuit which is is largely responsible for the
noise cancellation effect.
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DHA Directional Hearing Aid
Microphone Array Theory

• All microphones must be separated by a fixed
  distance to produce maximum cancellation of
  unwanted signals.
• Input and summing stages must have similar
  impedances so they do not cause a phase shift
  inside of the circuit.
• Having the microphones spaced four centimeters
  apart increases directionality for high
  frequencies because of their short wavelength.
• Low frequencies would require a larger spacing
  between microphones.

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DHA Directional Hearing Aid
Frequency Range Theory

• The frequency range is from 500Hz to 5.5KHz.
• Adjustable lower frequency cutoff switch- 500Hz
  to 1.5KHz
• Human ear loses high frequency first so more
  emphasis must be placed upon the base.
• Cascading low and high pass filters create the
  desired frequency range.

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DHA Directional Hearing Aid
Semester Accomplishments

• new circuit built, in testing phase
• Increased gain to 45 dB
• Finished auto-off design
• debugging circuit antenna problem
• redesigning the virtual ground

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DHA Directional Hearing Aid
Current Circuit
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DHA Directional Hearing Aid

• Summing amplifier and High pass stage.
• Directionality and low frequency cutoff occur
  in this stage
• Low pass Stage
• High frequencies are cutoff at this stage.
• Gain Stage
• The output signal is amplified during this
  phase.

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DHA Directional Hearing Aid
Debugging Process

• Antenna Problem Input
• Voltage leads act as an antenna and is bringing
  in a frequency of 33KHz

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DHA Directional Hearing Aid
Debugging Process

• Flaws in Virtual Ground Design
• Large current cannot be drawn from current
  design
• Gain loss occurs when a load resistance
  (headphones) is attached

Current Virtual Ground
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DHA Directional Hearing Aid
Proposed Solutions

• Solution for antenna problem.
• Relocate circuit to protoboard.
• New virtual ground design

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DHA Directional Hearing Aid
Implementation of auto-off feature
Future Circuit Design
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DHA Directional Hearing Aid
Future Semester Goals
Producing the Product

• Build Prototype of new circuit
• 2. Perform various tests
• Post prototype lab test
• Human subject test
• 3. Deliver the product

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SEM Sound Exposure Meter

• Presented by
• Maggie Zhu
• Jason Kaeding
• Greg Moore
• Guy Barcelona
• Jamy Archer

Project Partner Dr. Robert Novak, M. D. Steer
Audiology Clinic at Purdue
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Project Objectives

• Alert user when noise level could cause hearing
  damage
• Easy to use, easy to understand
• Small size (i.e. a pager)

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Desired Functionality

• Instantaneous indicator
• Current noise level gt 85dBA
• Average level indicator
• Avg. noise level for 1 min. gt 85dBA
• Impulse noise indicator
• Avg. frequency of impulses in excess of 110dBA gt
  1 per 3 sec.

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Overview ofCircuit Design
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SemesterAccomplishments

• Evaluated and consolidated impulse noise
  indicator section
• Redesigned A-weighting filter
• Created test plan

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Impulse Noise Indicator

• Tested current hardware configurations
• Consolidated counters and comparator into PLD
• Added continuous testing functionality.

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Filter Design

• Goal accurately model A-weighting transfer
  function

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Filter Design

• Design completed
• Three sections
• Each realizes one part of the transfer curve
• Used active Sallen and Key circuits
• SPICE simulation
• Max. deviation lt 0.6dB

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Test Plan

• Designed for the overall circuit
• Includes a standardized procedure and safety
  concerns
• Compares circuit response to the response of
  Sound Level Meter

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Future Plans

• Individually test each functional block
• Fine tune reference voltages in comparators
• Complete new circuit diagram
• Implement test plan for whole circuit

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VLM Voice Level Meter

• Tim Chuah
• Jason Fluckey
• Valerie Lamott
• Erica Lute
• Nate Miller

Project Partner Dr. Robert Novak, M. D. Steer
Audiology Clinic at Purdue
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Problem Identification

• Audiology Clinic needs a visual means of
  measuring speech volume.
• Existing device, Spright II, has been
  discontinued.

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Improvements

• Existing device is not very accurate.
• Longer cord or battery operated.
• Improve LED display readability.

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Design Concept

• 5 10-segment LED bar graphs
• Range of 40-89dB

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Block Diagram
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Circuit Diagram
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Project Status

• Low pass filter has been built and it works.
• Second low pass filter was designed and it also
  has been built and works.
• Log amp has been built and it works.
• Microphone through log amp working together

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Future Plans

• Add potentiometers
• Work on driver chips
• Work on casing

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