In this instructable, we will be building an intelligent hearing aid. The goal is to build a low power, cost-effective hearing aid that has several key intelligent features. First, it has tuning functionality that allows the wearer to tune the amplification to his or her needs. It has a conversational mode which recognizes voice input and amplifies it while reducing background noise. It saves all data to memory so that the device can be quickly powered up and ready to use. This device also has a very easy user interface to keep operation quick and simple.
The block diagram above outlines how the hearing aid works. A signal picked up by the microphone first goes through a pre-amp stage which culls frequencies above 3kHz (outside hearing spectrum) and then amplifies the remaining signal for future stages. The signal then progresses to the filter stage where it goes through four parallel filters that divide the signal into four frequency ranges. This filtered signal is read by the level estimator and provided to the Arduino. The filtered signal is also passed to the gain-controlled stage where the signals are amplified based on tuning settings provided by the Arduino. The signal finally enters the output stage where it passes through a summer and the modified signal can be heard with a pair of earphones.
Step 1: Design
The circuit for the hearing aid must accomplish several key tasks. First it has to amplify the microphone signal to a large enough level to be processed by the rest of the circuit. Next the signal has to be passed through a set of filters to split up the signal into four audio bands to be level estimated and then individually scaled. Finally the bands must be recombined and sent to a pair of headphones. The Arduino reads the levels of each band and scales the bands appropriately.
This project requires about $60 worth of parts. See cost table above. Please refer to the parts list attached for a full list.