Hearing aid. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Electronics in medicine

 Comments on the article

Over the years, my father developed hearing problems, and, according to a prescription, in the Medtekhnika store, after a whole year of waiting, he was given a "miracle of technology of the XNUMXst century" - a hearing aid. It was an ordinary hearing aid for the hearing impaired, produced by our own "and still" Soviet "radio industry.

It was made very badly: the circuit design and element base were outdated for a long time, the build quality and parts left much to be desired, and the parameters were simply none! The "miracle of technology" worked poorly (almost did not compensate for hearing loss) and not for long (miniature batteries "died" very quickly). Yes, and the very "charging" did not last long.

Recently opened "Hearing Prosthetics Center" offered a new generation device with programming parameters of the auditory canal. It seems to be good, but their prices are "biting", and, as it turned out later, they cannot compensate for a deep hearing loss either.

So I had to solve this problem myself. Where to start? From the piezoceramic microphone (can you imagine, it is still used in hearing aids!) I decided to immediately refuse, because. its frequency response is complete squalor. Now on sale there are electret microphones-tablets (with a built-in field-effect transistor amplifier) ​​from cell phones or modern telephone sets. These microphones have a flat frequency response and high sensitivity.

I also rejected the electromagnetic telephone primer, made explicitly on the model of the TM-4M (a kind of anachronism that stubbornly does not want to become a relic of the last century). Its frequency response is a match for a piezoceramic microphone, and the return (due to the high resistance of the winding) is low. With such a return, indeed, no hearing correction will work. For this purpose, I considered ordinary in-ear (in-ear) stereo headphones from portable players suitable.

As a basis for the circuit, I chose an amplifier for eavesdropping ("spy equipment"). After simplifying it a little, I got a completely working circuit of the hearing aid (Fig. 1), which fits into a standard case with dimensions of 128x66x28 mm.

(click to enlarge)

Resistor R1 sets the sensitivity of the BM1 microphone of the hearing aid. Capacitors C3 and C4 form the frequency response in the high-frequency region (they prevent self-excitation in ultrasound and prevent overloading the amplifier at higher audio frequencies). Capacitor C5 forms the frequency response at low frequencies (removes the "mumbling" of the microphone). Resistor R8 sets the operating point of the output stage: the voltage at the emitters VT4 and VT5 should be half the supply voltage.

On the transistor VT6 assembled battery status indicator GB1. Resistor R12 sets the ignition voltage of the VD2 LED at 4 V, which corresponds to the minimum allowable battery voltage. As VD2, a green LED with a diameter of 2 mm of increased light output of the Piranha series is used.

The battery consists of four cells with a capacity of 500 ... 1000 mAh. The VD3 LED indicates charging (it goes out after it is completed). Red AL3 is used as VD307. Zener diodes VD4 and VD5 are selected to limit the voltage (with the charging unit connected) at a level of 7,3. ..7.4 V. The output connector X1 uses a simple plastic stereo jack for mounting on the board. The right and left channels are paralleled on the printed circuit board in it, as this improves the return of the headphones. Since such nests do not last long, I recommend placing two of them in parallel at once. This will allow you not to waste time repairing (replacing) one jack - you just need to insert the earphone into another jack.

The shape, arrangement of parts on the board and the drawing of the printed circuit board are shown in Fig.2-4. The BM1 microphone is installed in a soft rubber yoke fixed inside the case with silicone adhesive-sealant.

(click to enlarge)

The battery charging unit is made from a universal power supply ("Chinese") for electronic equipment (Fig. 5). It uses the third (bottom) tap of the secondary winding of the transformer for operation. The idle voltage at the output is about 9,7 V, the charging current at the specified R1 rating is about 50 mA. One battery charge is enough for 3-5 days of hearing aid operation. The device allows simultaneous operation and charging.

The sound pressure created by this hearing aid (I did not have the appropriate measuring instruments) is so great that it creates pain for a normally hearing person and subsequent temporary (several minutes) deafness. My father, who has a profound hearing loss, received almost complete hearing compensation with good intelligibility with this hearing aid.

When repeating the design, special attention should be paid to the headphones. Some of them are not able to create a sufficiently large sound pressure, either due to large ohmic resistance, or due to low efficiency (read quality). On-ear headphones with a headband and soft ear cushions for Hi-Fi equipment can give a good effect. However, the use of such headphones is possible only with a good fit of the ear pads.

It is useful to install a latch on the front wall of the hearing aid housing for attaching it to the breast pocket flap. It makes sense for experienced radio amateurs to work on reducing the size of the hearing aid by switching to microcircuits and miniature batteries.

Author: V.Zakharenko, UA4HRV, Samara

See other articles Section Electronics in medicine.

Read and write useful comments on this article.

<< Back

Latest news of science and technology, new electronics:

The world's tallest astronomical observatory opened 04.05.2024

Exploring space and its mysteries is a task that attracts the attention of astronomers from all over the world. In the fresh air of the high mountains, far from city light pollution, the stars and planets reveal their secrets with greater clarity. A new page is opening in the history of astronomy with the opening of the world's highest astronomical observatory - the Atacama Observatory of the University of Tokyo. The Atacama Observatory, located at an altitude of 5640 meters above sea level, opens up new opportunities for astronomers in the study of space. This site has become the highest location for a ground-based telescope, providing researchers with a unique tool for studying infrared waves in the Universe. Although the high altitude location provides clearer skies and less interference from the atmosphere, building an observatory on a high mountain poses enormous difficulties and challenges. However, despite the difficulties, the new observatory opens up broad research prospects for astronomers. ... >>

Controlling objects using air currents 04.05.2024

The development of robotics continues to open up new prospects for us in the field of automation and control of various objects. Recently, Finnish scientists presented an innovative approach to controlling humanoid robots using air currents. This method promises to revolutionize the way objects are manipulated and open new horizons in the field of robotics. The idea of ​​controlling objects using air currents is not new, but until recently, implementing such concepts remained a challenge. Finnish researchers have developed an innovative method that allows robots to manipulate objects using special air jets as "air fingers". The air flow control algorithm, developed by a team of specialists, is based on a thorough study of the movement of objects in the air flow. The air jet control system, carried out using special motors, allows you to direct objects without resorting to physical ... >>

Purebred dogs get sick no more often than purebred dogs 03.05.2024

Caring for the health of our pets is an important aspect of the life of every dog ​​owner. However, there is a common assumption that purebred dogs are more susceptible to diseases compared to mixed dogs. New research led by researchers at the Texas School of Veterinary Medicine and Biomedical Sciences brings new perspective to this question. A study conducted by the Dog Aging Project (DAP) of more than 27 companion dogs found that purebred and mixed dogs were generally equally likely to experience various diseases. Although some breeds may be more susceptible to certain diseases, the overall diagnosis rate is virtually the same between both groups. The Dog Aging Project's chief veterinarian, Dr. Keith Creevy, notes that there are several well-known diseases that are more common in certain breeds of dogs, which supports the notion that purebred dogs are more susceptible to disease. ... >>

Random news from the Archive Volcanoes and plague 23.04.2001 Climatologist Richard Stothers from the Goddard Institute for Space Research (USA), having studied historical documents, ice samples drilled from great depths of the Greenland glaciers, and rings on cuts of old trees, claims to have found a connection between large volcanic eruptions and plague epidemics. Over the past 2000 years, there have been seven powerful eruptions, each of which has thrown at least one hundred million tons of dust and gases into the atmosphere. And in five cases out of seven, an epidemic of bubonic plague swept through the Old World shortly after the eruption. Volcanic dust brought into the upper atmosphere weakens the solar radiation reaching the Earth's surface. As a result, cold air currents are shifting to the south, in Europe and the Middle East the climate becomes colder and more humid, which contributes to the spread of plague bacilli. Plague-carrying rats try to stay closer to human dwellings and food supplies because of the cold snap. Then the epidemic begins.

Other interesting news:

▪ Protein semiconductor

▪ Silver nanowire instead of ITO film

▪ A cow the size of a dog was bred

▪ LMX9838 - Bluetooth module with serial port profile

▪ Apple's eye-tracking 3D interface

News feed of science and technology, new electronics

Interesting materials of the Free Technical Library:

▪ section of the site Reference materials. Article selection

▪ article Oh, it's not an easy job to drag a hippopotamus out of the swamp! Popular expression

▪ article When will the sun go out? Detailed answer

▪ article Rosehip. Legends, cultivation, methods of application

▪ article Radar. Encyclopedia of radio electronics and electrical engineering

▪ article Frequency divider by 5000. Encyclopedia of radio electronics and electrical engineering

Leave your comment on this article:

All languages ​​of this page

Arabic	Hebrew	Polish
Bengali	Hindi	Portuguese
Chinese	Italian	Spanish
English	Japanese	Turkish
French	Korean	Ukrainian
German	Malay	Vietnamese

Home page | Library | Articles | Website map | Site Reviews

www.diagram.com.ua
2000-2024