Mother's Under-$30 Hearing Aid

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THE LIMITATIONS

Before I go any further, let me point out, once again, that this hearing aid won't solve every hearing loss problem. Although it has quite a bit of amplification and provides for tonal control, it obviously isn't tailored to suit an individual's specific hearing problem. Much of what you pay for when buying a commercial hearing aid is the testing and custom design that match the device to the specific hearing problem that you have. Consequently, our amplifier lacks the refinement of custom hearing aids.

On the other hand, though, MOM's hearing aid is likely to cost at least several hundred dollars less than a commercial model. So if you have a mild impairment, and if your doctor agrees that a hearing aid is likely to help, you should consider giving our design a try.

BUILD IT

At the time that this project was conceived (thanks to the suggestion of reader John S. Coe, who has built an aid of his own design), we decided that it would be next to impossible to make a concealed hearing aid, such as a behind-the-ear or eyeglass-mounted model. Even if a person were able to master the miniature-construction skills required, procuring the necessary tiny parts would be difficult indeed. Therefore, we decided to concentrate on a model that has most of its works in a compact plastic box . . . one that would fit into a pocket.

Duplicating our hearing aid is fairly simple; the device shouldn't take more than a couple of hours to construct once you've rounded up the parts. In the interest of simplicity, we decided to incorporate the amplifier part of the unit into a printed circuit board. You can make your own from the accompanying illustration or—easier still—purchase one from Danocinths (see the parts list for ordering information). Once you've got an etched and drilled board, just insert the components according to the parts layout, and solder them in place. (Be sure to pay attention to semiconductor orientation and polarity!)

There are four essential components that are not included on the circuit board: a microphone, an earphone jack, the clarity control, and a battery holder. These pieces must be mounted inside the plastic case and wired to the printed circuit board. The directions that follow will tell you how to proceed. When using them, hold the plastic case in your hand so that the long dimension is vertical and you're looking into the cavity.

The microphone goes in a hole in the upper right-hand corner of the bottom of the case. For best results, drill the hole to about 11/32" so that the 3/8"—diameter microphone will fit snugly in place. Push the microphone into the hole-you may have to file the opening a little larger-until it protrudes slightly beyond the outside of the case, then secure it with glue.

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