Team Members:Noah Van FossanShareen HossainDeepthi ChandraChristina ClemenzLaura Hanley

Advisors:Prof. Mark BellProf. Carla Zoltowski

Project Partner: Prof. Robert Novak

DHA Directional Hearing Aid

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.

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.

Project Goal

Overview

DHA Directional Hearing Aid

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.

Microphone Array Theory

DHA Directional Hearing Aid

DHA Directional Hearing Aid

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.

Frequency Range Theory

DHA Directional Hearing Aid

• new circuit built, in testing phase

• Increased gain to 45 dB

• Finished auto-off design

• debugging circuit antenna problem

• redesigning the virtual ground

Semester Accomplishments

DHA Directional Hearing Aid

Current Circuit

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.

DHA Directional Hearing Aid

• Antenna Problem Input

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

Debugging Process

DHA Directional Hearing Aid

Flaws in Virtual Ground Design

• Large current cannot be drawn from current design

• Gain loss occurs when a load resistance (headphones) is attached

Debugging Process

Current Virtual Ground

DHA Directional Hearing Aid

Solution for antenna problem. • Relocate circuit to protoboard.

New virtual ground design

Proposed Solutions

DHA Directional Hearing Aid

Implementation of auto-off featureFuture Circuit Design

Producing the ProductFuture Semester Goals

DHA Directional Hearing Aid

1. Build Prototype of new circuit

2. Perform various tests

Post prototype lab test

Human subject test

3. Deliver the product

Presented by:Maggie ZhuJason KaedingGreg MooreGuy BarcelonaJamy Archer

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

SEM Sound Exposure Meter

Project Objectives Alert user when

noise level could cause hearing damage

Easy to use, easy to understand

Small size (i.e. a pager)

Desired Functionality Instantaneous indicator

• Current noise level > 85dBA

Average level indicator• Avg. noise level for 1 min. > 85dBA

Impulse noise indicator• Avg. frequency of impulses in excess of

110dBA > 1 per 3 sec.

Overview ofCircuit Design

Instantaneous IndicatorAverage Level Indicator

Impulse Noise Indicator

SemesterAccomplishments

Evaluated and consolidated impulse noise indicator section

Redesigned A-weighting filter

Created test plan

Impulse Noise Indicator

Tested current hardware configurations

Consolidated counters and comparator into PLD

Added continuous testing functionality.

Filter Design Goal: accurately model A-weighting

transfer function

Filter Design Design completed

•Three sections

• Each realizes one part of the transfer curve

• Used active Sallen and Key circuits

•SPICE simulation

• Max. deviation < 0.6dB

Test Plan

Designed for the overall circuit

Includes a standardized procedure and safety concerns

Compares circuit response to the response of Sound Level Meter

Future Plans

Individually test each functional block

Fine tune reference voltages in comparators

Complete new circuit diagram

Implement test plan for whole circuit

Tim ChuahJason FluckeyValerie Lamott

Erica LuteNate Miller

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

VLM Voice Level Meter

Problem Identification

Audiology Clinic needs a visual means of measuring speech volume.

Existing device, Spright II, has been discontinued.

Improvements

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

Design Concept

5 10-segment LED bar graphs

Range of 40-89dB

Block Diagram

Circuit Diagram

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

Future Plans

Add potentiometers Work on driver chips Work on casing