Hearing Profiles

Hearing profiles, or audiograms, vary from person to person. The audiogram specifies the minimum amplitude of sound an invididual is able to hear. For example, in Figure 1, the blue line delineates what the minimum amplitude of the sound at the specified frequency the individual is able to hear. In this case, the individual's needs a sound at 4000 Hz to be a minimum of 60 dB to be hear, which is very poor. The ideal range for minimum dB level is above 20 dB across all frequencies.

The goal of our hearing aid is to be tunable to accomodate these various audiograms. The following is an example of a common type of audiogram for a hearing impaired person. 

Figure 2: Sensorineural Hearing Loss

In Figure 1, you will see an example of sensorineural hearing loss, which is the most common type of hearing loss. 90% of hearing impaired people have this type of hearing loss in which there is damage to the inner ear. 

Figure 2: Conductive Hearing Loss

Figure 2 is an example of conductive hearing loss in which the outer or middle ear are not properly working. This causes a block. 

Figure 3: Mixed Hearing Loss

Figure 3 is an example of mixed hearing loss. Expectedly, this is a mix of both conductive and sensorineural hearing loss. 

Our ideal tunable hearing aid system would attempt to amplify the frequencies for which the individual requires a larger minimum amplitude. In particular, a set of selectively tuned band pass filters would amplify the frequency ranges in which the individual has poor hearing. This set of band pass filters will be tuned by modifying programmable resistor values within each bandpass filter circuit. In particular, the band pass filters can be modified for a different corner frequency, quality factor (or width), and amplitude. 

Based on the above, we may want to focus more on improving the hearing aid performance for sensorineural hearing profiles, since the vast majority of hearing impaired people suffer from this type of hearing loss. Sensorineural hearing may require also having the ability to increase decrease the attenuation of the filter and having a large amplitude, which may require using higher order band pass filters. 

Project Proposal

Project Title: Tunable Analog Hearing Aid

Team Members: Golam Kibria, Alex Perry

Motivation: Current hearing aid solutions amplify all frequencies of sound. However, hearing frequency profiles vary depending on the user. A programmable hearing aid solution would allow the user to customize the hearing aid to their preferences and needs. Additionally, it would allow the user to modify the hearing aid as the user’s hearing abilities change, for example, due to aging.

Goals:

1. Design a hearing aid that can be modified by the user to amplify a certain set of frequency ranges
2. Allow the user to program the hearing aid through a simple mechanism, such as USB
3. Create a microcontroller based interface for the user to input the frequency ranges they desire to amplify and the magnitude of amplification
4. Create a gui that displays the characteristics of the amplifier, allows the user to modify the parameters, and generate code to enact the change

Methodology

1. Research hearing profiles of those who use hearing aid to determine number of variable bandpass filters required to get the necessary distribution
2. Research various types of bandpass filters to determine ideal types for this application
1. Power consumption
2. Signal quality
3. Number of components
4. Configurability using digital potentiometers
3. Use circuit simulations to compare potential circuits (CircuitLab frequency analysis)
4. breadboard chosen circuit for real world testing
5. Prototype programming software to take user input, compute necessary variable parameters, and program hearing aid

Testing and Evaluation

Circuit simulation

• We will simulate potential circuits in CircuitLab to characterize performance and determine the most ideal circuits

Physical Prototype

• We will create a breadboard prototype to determine real world performance of the chosen circuit. We will test the signal outputs through an oscilloscope and the audio quality of the output

Project Components

Hardware

Band pass filters(capacitors, op amps, programmable potentiometers, resistors)

Summing Amplifier circuit

Microphone

Speaker

Mbed for programming circuit elements.

Software

Python GUI to allow user to specify (frequency range and?) amount of amplification

Microcontroller software to take gui input over USB and translate into a series of I2C or SPI commands to send to programmable circuit elements

Deliverables

Baseline:

Breadboard prototype using programmable components

Basic software to generate I2C or SPI messages

Reach:

PCB with low power components

GUI to program various components

Timeline

By 4/8	Perform research on hearing profiles and bandpass filters Create circuit simulation to test various band pass filters
4/9-4/15	Finish simulation testing and breadboard circuit with fixed components Order programmable parts
4/16-4/22	Breadboard circuit with programmable circuits. Build simple UI to program components. Design PCB
4/23-4/28	DEMO DAY - Finalize initial prototype
4/29-5/6	Assemble PCB Program GUI for interfacing with circuit.
5/10	Hand in report and github.