Low-Cost Digital Hearing Aid

Electrical Engineers: Bemnet Azage, Alvin Grant

Computer Engineers: Kermit Strachan, Hansol Kim

Team Leader: Bemnet Azage (btegegnework2007@my.fit.edu)

PRELIMNARY DESIGN REVIEW

October 18, 2011

ContentsProject Description................................................................................3

Basic Visualization.................................................................................4

Person wearing an external Digital Hearing......................................4

Specifications.........................................................................................4

Figure 4: Suggested Fitting Range Chart............................................5

Expected Results...................................................................................6

Circuit Design.........................................................................................8

Features.............................................................................................9

Task Schedule......................................................................................12

Project Tasks........................................................................................12

Design Options....................................................................................13

Final Decision Rationale......................................................................14

Block Diagram......................................................................................15

Team Members & Organization Chart.................................................16

Competitive Analysis...........................................................................17

Bill of Materials...................................................................................18

Project Analysis...................................................................................19

Risk Analysis........................................................................................20

References...........................................................................................22

Competitive Analysis...........................................................................22

Project Description

The goal of our project is to design a low cost external digital hearing device, using Digital Signal

Controller (DSC) technology. The external digital hearing aid would be attached onto the user’s belt

or can be put into their pocket. A headphone would be wired from the hearing device to the user’s ear

and the device will consist of most of the advance features but at a very inexpensive price. This

device is designed for the millions of people over the world who suffer from hear loss and the many

people that cannot afford to buy any corrective aid instruments.

The finished result of our low cost external digital hearing aid is expected to have the following

features:

unidirectional and omnidirectional microphones designed to receive sounds from different

directions

Digital noise reduction

Digital feedback reduction

Digital speech enhancement

The telecoil technology that improve sound quality in device such as telephones, TVs, radios

etc

Basic Visualization

Specifications

Generally, in order for a hearing-impaired person to use a hearing aid, he/she has to go to an audiologist and take an audiogram test. A person who has perfect hearing normally hears so at a gain 25dB but this can vary drastically with a hearing-impaired person depending on the extent of hearing loss. Based on the audiogram test, the DSP of the digital hearing aid will be programmed to meet the users need. Figure 4 shows the results of the typical hearing test. Our hearing aid design would be base on the result of these results. Therefore, our digital hearing aid would be suitable for persons with the below hearing results or similar results.

A Hearing Aid for Moderate Hearing Loss

Hertz RateIf you have a

Maximum Decibel Hearing loss

125 - 500 40 dB

501 - 1K 50 dB

1K - 4K 60 dB

4k - 8K 70 dB

Figure 4: Suggested Fitting Range Chart

Our Digital hearing aid design consists of three channels. Channels are bands of frequencies that can be adjusted and programmed based on the user’s need and it consist in most hearing aids in order to achieve high sound quality.

In our design, the frequency ranges for each channel is as follows:

Low Frequency Channel – 125Hz to 500Hz (for loud sounds) Mid Frequency Channel – 500Hz to 2000Hz (for moderate sounds) High Frequency Channel – 2000Hz to 8000Hz (for soft sounds)

The DSP would be programmed to facilitate these channels. It would read the frequency of the incoming signal and know how much gain to apply to the signal. Therefore, if a sound between 125 Hz and 500 Hz is received by the hearing aid, the DSP would read the frequency and apply a gain of 15dB to 25dB

Based on the targeted model of our hearing aid design, see Figure 4, there will be different gains for each channel. Looking at Figure 4, the Low Frequency Channel requires a gain of 15dB to 25dB, Mid Frequency Channel requires a gain of 25dB to 35dB and the High Frequency Channel requires a gain of 35dB to 45dB. For example, if the incoming sound has a frequency of 400 Hz, then the sound would be processed to the mid channel that would already be programmed to apply a gain of 35db to 45 db.

There are constant and time-varying sounds; an air-conditioning unit carries a constant humming sound and a person’s voice has different tones at different times. We can program the DSP to compare whether the incoming sound is constant or time varying. Therefore, the constant humming from the air conditioning unit can be cancelled or filtered and the wanted sound, someone speaking for example, can be processed.

All sounds below 125 Hz and above 8000 Hz will be automatically cancelled out by using a band pass filter. The hearing aid will be designed with low gain for the low frequency sound, medium gain for moderate frequency sound and high gain for the high frequency sound. Therefore, a low pass filter would be used when we want to pass low frequencies but attenuate higher frequencies and high pass filter when we want to pass high frequencies but attenuates low frequency. After frequency pass the filtering, the signal can be amplified with the necessary amount of gain in each channel based on the users need.

Expected Results

What we are expecting from our prototype is summarized in the table below.

Parameters Values

Maximum Output (db) 130

Minimum Output (db) 60

Battery Size Energizer ECR1025 3V Lithium Batteries

Battery Life (HR) 284

Frequency Range (Hz) 125 - 8000

Number of Channels 3

Feedback Noise Management Yes

Automatic Noise Reduction Yes

Telecoil Yes

Circuit Design

Circuit model: MPLAB dsPIC33F Digital Signal Controllers Evaluation Module

Specifications:

- dsPIC33FJ256GP506 DSC with 256 KB Flash and 16 KB RAM - 16/24/32 bit codec with a maximum sampling frequency of48KHz - Microphone and line level inputs with adjustable input gain - 100mW headphone amplifier with digital volume control- 4 Megabit serial flash memory for application use

Energizer CR1025 3V Lithium Coin Battery 700 hrs

Knowles FG/BFG Series Microphones

Features

Small size is ideal for multiple applications Rugged High resistance to mechanical shock Exceptionally low vibration sensitivity Various responses available Integral RFI suppression BFG offers improved Power Feed-through Attenuation, improved settling time, and electrical high

pass filter

Custom corner frequencies achieved through electrical high pass filter optimize noise performance at low frequencies for demanding matching and directional applications

Features Philips SHH8006/28 High performance Headset

Flexible, Rubber Ear Hooks for a Secure Fitlong 1.2-meter (47-inch) cable gives you freedom of movement, and three interchangeable rubber ear caps ensure a comfortable fit.

Passive Noise IsolationUsing passive noise isolation to deliver superb sound even at low volume levels, the SHH8006/28

eliminates distracting background noise through the snug in-ear fit, so all you'll hear is rich, clear acoustics. The tiny, efficient speaker driver provides superior audio, and the 24k gold-plated connector plug ensures a reliable connection.

Environmental Specification

The low cost digital hearing aid is designed to be used in outdoor and indoor environment.

However, hearing aid to get wet or be used in water, the rain etc.

Runtime Specification

The runtime specifications are based on the battery life of the two 3V Lithium Batteries

we will be using. (700 hours)

Battery Specifications:

Classification: "Lithium Coin" Chemical System: Lithium / Manganese Dioxide (Li/MnO2)

Designation: ANSI-5033LC, IEC-CR1025

Nominal Voltage: 3.0 Volts

Typical Capacity: 30 mAh (to 2.0 volts)

(Rated at 68K ohms at 21°C)

Typical Weight: 0.7 grams (0.02 oz.)

Typical Volume: 0.2 cubic centimeters (0.01 cubic inch)

Max Rev Charge: 1 microampere Energy Density: 124 milliwatt hr/g, 435 milliwatt hr/cc

Typical Li Content: 0.009 grams (0.0003 oz.)

Classification: "Lithium Coin" Chemical System: Lithium / Manganese Dioxide (Li/MnO2)

Designation: ANSI-5033LC, IEC- Nominal Voltage: 3.0 Volts

Condition Specifications

Temperature Industrial temperature range (-40°C to +85°C) Radiation Able to operate in full sun

Safety Specification

Kill Switch One manual power on/off button

Power Management On-chip 2.5V voltage regulator

Temperature Sensor

Task Schedule

Project Tasks

Research design and cost of the digital hearing aid.

Program the digital signal controller (DSC).

Simulating the design

Determine components that are needed for the project and order them

Building the digital hearing aid.

Below shows the Ghant Chart, that reveals the schedule of our project

Research design and cost of the digital hearing aid.

Programming DSP

Simulating the design

Determine components that are needed for the project and order them

Fusing the hardware and software

Building Digital Hearing aid

8/25/11 10/14/11 12/3/11 1/22/12 3/12/12

Start DateDays Completed

Design Options

Electronic Circuit Board:

Option A: This option uses the EVMOMAP-L137 (DSP) board just like the labs in the Microcomputer systems I, and by doing so, we could utilize the board to create filters and get the DSP board to be customized for our digital hearing aid. This option was promising due to the fact we have tried to make the filters in the lab and to some degree, succeeded.

Option B:Second option is for us to use dsPIC (DSC) board since it is more capable of being used and adapted onto the digital hearing aid’s physical form. Programming would be a little different from what we know, but we do know that it runs in C programming language and applying and designing filters should be similar.

Pros Cons:

Option A Faster processing speed Almost impossible to solder with hands

Easier implementation than DSP Easy to use

Option B Easier implementation than DSP Slower processing speed

Having fewer and solderable pins Not familiar with the interface

Final Decision Rationale

After careful consideration of the options and the component options we have, our team has

agreed upon following resolutions:

The headphone piece has to have microphones attached. Having the microphones near the

earphone speakers increases our risk of having feedbacks with loud output of the speakers, but

it’s the only way to get close to 360 degrees omni-directional input for the user. Utilizing the

headset like Philips shown above will give us chances to apply a small microphone on the plastic

part that holds the headset to the ear.

In terms of the electronic board and the main component of the digital hearing aid, team finds the

dsPIC DSC board to be effective rather than the DSP board. The reason behind the conclusion

was made after researching the specifications of the two boards and a help from our resource,

Jacob Zurasky, the Microcomputer systems I graduate assistant kindly pointed out for us the

difficulty we would face if we decided to customize the board. With dsPIC DSC board, we are

able to easily customize it physically compared to the DSP board, but with one flaw, it’s

processing speed.

After these two main steps are finished, there are the matters of programming the board and

connecting the wire from the headset to the board. These will be the most challenging steps,

since it’s in the program used in the dsPIC DSC board isn’t familiar to us. The team believes in

the steps we’ve taken and will carry out as planned in our schedules.

Block Diagram

DSC

Team Members & Organization Chart

Bemnet Azage Team Leader

Software Design

Kermit Strachan

Sub Leader of software design

Hansol Kim

Coordinator of software and hardware design

Hardware Design

Alvin Grant

Sub Leader of Hardware design

Competitive Analysis Types of Digital Hearings Aids

Style Number of channels

DirectionalMicro-phones

Frequency Range

FeedbackCancellation

Noise Reduction

Speech Enhancement

Memories VolumeControl

Battery Cost

Low-Cost Hearing aid

Externaldevice

3 channels YES 125Hz-8000Hz YES YES YES 2 Manual 13 –(284 hrs)

$150.00

Rosebud Basic In the Ear

N/A NO 125Hz-8000Hz YES YES N/A N/A Manual 10A - (100 hrs)

$299.00

Audition Basic In the Ear

N/A NO 125Hz-8000Hz YES YES N/A N/A Manual 13 –312 hrs

$499.00

Rosebud Premium

Completely

In the Ear

N/A NO 125Hz-8000Hz YES YES N/A 4 Manual 10A –(100 hrs)

$599.00

Audition SP Basic

Behind the Ear

N/A NO 125Hz-8000Hz YES YES YES 2 Manual 13 –(284 hrs)

$499.00

Audition Super High

Power

Behind the Ear

N/A YES 125Hz-8000Hz N/A YES N/A N/A Manual(675 hrs)

$699.00

Rosebud SP Premium

Behind the Ear

12 Bands / 8 channels

Yes 125Hz-8000Hz YES YES YES 4 Manual 13 –(284 hrs)

$899.00

Rosebud Basic Open Fit Ready to

Wear

Mini Behind the Ear Open Fit

1 Band / 2 channel

Yes 125Hz-8000Hz YES YES YES 2 N/A(312 hrs)

$499.00

Audition Basic Open Fit

Mini Behind the Ear Open Fit

12 Bands / 2 channels

Yes 125Hz-8000Hz YES YES N/A 4 Manual 10A - (100 hrs)

$599.00

Rosebud Premium Open Fit

Mini Behind the Ear

12 Bands / 2 channels

Yes 125Hz-8000Hz YES YES YES 4 Manual (312 hrs) $699.00

Audition Premium AD

Open Fit

Mini Behind the Ear

12 Bands / 4 channels

Yes (2 Adaptive

Directionality)

125Hz-8000Hz YES YES YES 4 Automatic 10A - (100 hrs)

$899.00

Audition Receiver in

the Ear

Receiver in the Ear

3 Yes (1 receiver in ear

canal)

125Hz-8000Hz YES YES YES 4 Automatic(312 hrs)

$11990.00

Bill of Materials

Quantity Manufacture Description Price

1 Microchip MPLAB dsPIC33F Digital Signal Controllers

Development board

$65.00US

2 Knowles FG/BFG Series Hearing aids Microphone $30.00

2 Energizer CR1025 3V Lithium Coin Battery $10.00

1 Phillips High performance Headphones $15.00

1 Miscellaneous Company Covering $100.00

N/A Miscellaneous Companies Electronic components: battery holder, cables etc $50.00

N/A N/A Miscellaneous $50.00

Total S320.00

Project Analysis

This section of the document contains the estimated results, costs and period for the project.

Based on our proposed schedule, this project will take a maximum of 220 days to be completed.

One workday is the equivalent of 8 hours of work, which can span over multiple days, weeks or

months. With 4 members on the team, each member will contribute an average of 23 workdays

or 184 hours each on the project. Workday estimates are based on previous tasks, the complexity

of the task, and the amount of people working on it. The actual amount of time spent may be

significantly less than the man-day estimate, as the man-day is the maximum amount of time that

is estimated to complete the task. This estimate does not take into consideration any other

responsibilities or issues that may arise outside of the project scope.

Financially, it is expected that this project will have a low-cost budget. The reason for this is

that the project consists mainly of design and simulation of the digital hearing aid device.

Finding and utilizing the most appropriate and efficient software for this project, maybe the only

financial concern temporarily. After more thorough research, we expect to compare and contrast

prices, performance and durability of components, materials and chips that may be used in the

building phase of the device. Overall, one of the goals is to produce a device that performs well,

but has a lower cost compared to those on the market; thus the proposed budget is expected to be

low-cost.

The project team trusts that this project will be completed on time. Each member has been

assigned to a specific department and is responsible for the tasks assigned to them by the project

leader. Dr. Venton Kepuska, known for his work in speech recognition and voice processing,

will be advising and providing assistance. The focus is to gather as much information as possible

to optimize and produce a more accurate and efficient final product. The final, expected result is

a working simulation of a digital hearing aid. The team hopes that the final simulation can then

be transformed into the physical device.

Risk Analysis To win you have to risk loss. ~Jean-Claude Killy.

Our project is challenging, and it needs the combined effort from everyone in order to

successful. Our project requires a lot of time for research for each stage the design. We have to

compare and contrast which materials are better suited to accomplish our goal of a more

affordable digital hearing aid. The main uniqueness of digital hearing aid relies on the Digital

Signal Processing (DSP), which needs extensive work to be programmed to fulfill all the desire

functions needed. Finally yet importantly, our project requires the suitable software for the

simulation and design of the hearing aid so we can precisely observe our results.

Schedule:-

One of the reasons for project failure is not finding appropriate time to communicate

between team members. Since the each team member works extensively on campus along

with our class work, it has been difficult finding a good time to meet with each other. We

still have not found a regular time to meet weekly and discuss about the project.

Technical:-

Each member in our team is familiar with PSPICE, MULTSIM for computer simulation

but our project requires more advanced software simulation. Furthermore, we have not

found the best software for simulating this project.

Resource:-

As we mentioned before, the Digital Signal Processing is the key part of our project and

so far we have not found find extensive information about the programming language

that needs to use and how to implement it.

In addition, this project is the first time Florida Tech has engaged in a project on digital

hearing aids therefore, we do not have resources of past projects to help us.

Generally, we are hoping to work out these problems and any other issues that might arise. In

case the group members do not find time to meet, we agreed to contact each other through email

and by using Google Document Sharing to update each other with the progress of the project. If

we do not find suitable software that can help us simulate our digital hearing aid, we would have

to use our project budget to purchase the software. In addition, Associate Professor Dr. Venton

Kepuska has shown much interest in our project and he is willing to help us as much as he can.

Dr. Kepuska specializes in speech recognition and voice processing so he would be an excellent

resource.

References

Project Webpage: http://my.fit.edu/~kstrachan2008/JuniorDesign/index.html

Suggested Fitting Range Chart

http://hearingaidscentral.com/Details_Open_Ear_Hearing_Aid_Melody_A1.asp

Prototype of the Digital Hearing Aid to be designed http://www.youtube.com/watch? v=D1XnaqNKaMo&playnext=1&list=PL449C260AFE37FF94

Budget

http://www.altex.com/Semiconductors-Diodes-C10676.aspx

http://www.microcenter.com/single_product_results.phtml?product_id=0350262

Competitive Analysis

http://deafness.about.com/od/hearingaids/tp/Hearing-Aid-Manufacturers.htm

***Other useful sources of information***

Wireless Hearing Aid System Simulations using Advanced Design System™: A Behavioral Modeling ApproachRam Singh Rana1, Tang Bin2, Zhang Liang3, Garg Hari Krishna4, Wang De Yun5

Bond Graph Based Sensitivity and Uncertainty Analysis Modelling for Micro-Scale Multiphysics Robust Engineering Design

M. A. Perry, a,_ M. A. Atherton, b R. A. Bates, a H. P. Wynn. a

Design of a Digital Hearing AidKeith A. Mullins

Low-Power Real-Time Programmable DSP Development Platform for Digital Hearing AidsTrudy Stetzler, Neeraj Magotra, Pedro Gelabert, Preethi Kasthuri, Sridevi Bangalore

Digital Signal Processing of Speech for the Hearing ImpairedN. Magotra, F. Livingston, S. Savadatti, S. Kamath

Design of high-performance digital hearing aid processorYoung-cheol Park, Dong-wook Kim and In-young Kim