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TRANSCRIPT
Low-Cost Digital Hearing Aid
Electrical Engineers: Bemnet Azage, Alvin Grant
Computer Engineers: Kermit Strachan, Hansol Kim
Team Leader: Bemnet Azage ([email protected])
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