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 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

 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 feature Future Circuit Design

Producing the Product Future 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 Zhu Jason Kaeding Greg Moore Guy Barcelona Jamy 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 of Circuit Design Instantaneous Indicator Average Level Indicator Impulse Noise Indicator

Semester Accomplishments 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 Chuah Jason Fluckey Valerie Lamott Erica Lute Nate 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