Hearing aid electronics 03 circuit diagram. Hearing aid

Many people today experience hearing problems and the scale of this disaster is impressive. In addition to the elderly, many younger generations will also face hearing loss in the future, fueled by the rampant use of headphones and youth's love of discos.

Consequently, the question of how to make a hearing aid with your own hands will always be relevant, because the cost of such branded hearing aids is often beyond the means of many people.

In fact, making a hearing aid with your own hands is quite simple, for this purpose, available tools are used that anyone can easily find.

The resulting hearing aid is compact in size and can easily fit into an ordinary Bluetooth headset.

To get started, you will need a microphone - a regular microphone from a mobile phone will do. If this is not the case, then you can successfully use a microphone from a tape recorder. The tape recorder is quite ordinary, Chinese - the main thing is that the microphone has greater sensitivity.

Now let's move on to considering the circuit of the hearing aid. As you can see, the scheme is quite simple.

You should also use an earphone from your mobile phone as a speaker. The earphone must have quite high resistance, about twenty-five to forty ohms.

To power the device, a lithium tablet is used (voltage three volts). If you couldn’t find a lithium tablet, you can use three batteries from a regular wristwatch. The battery connection configuration is in series, and the total voltage should be 4.5 volts. When assembling, special attention should be paid to the microphone and its polarity - the microphone must be connected in the correct way.

If you have the desire and opportunity, you can use a lithium-ion battery from a Bluetooth headset instead of the option discussed above. With a capacity of 80-120 milliamps and a voltage of 3.7 volts, the lithium-ion battery will allow the hearing aid to work longer and can be recharged. The following types of transistors can be used for the device: S9014 and S9018, as well as transistors KT315 and KT368.

Let's go further in studying the question of how to make a hearing aid with your own hands. To reduce the size of your device, you should use SMD components. In order to increase the sensitivity of the hearing aid, you can replace the non-polar capacitor according to the microphone used by 0.01 microfarad.

Assembling the hearing aid.

When assembling a hearing aid, you need to ensure high-quality isolation of the microphone from the speaker - otherwise, background will form during use.

Another version of the device has two cascades that enhance the operation of the microphone. Since the microphone tablet itself has a built-in amplifier (single-stage), the result is a hearing aid with increased sensitivity, about 9-10 meters. You simply need add a simple amplifier, operating on a single transistor (similar to the amplifier used in the previous stage).

The first type of hearing aid has a current of 5 milliamps per hour, the second - about 10 milliamps/hour.

Such a hearing aid will work continuously and you won't need to turn it off, so there's no need for a switch.

Similar factory-produced devices are quite expensive, while the option discussed in this article will be inexpensive and will not be inferior in quality to factory samples.

This circumstance is especially important for pensioners and people with low incomes who cannot afford to purchase a branded hearing aid. You can please your grandparents, or help a colleague or friend overcome hearing problems. It is enough just to take all the necessary elements listed above and independently construct a device that can help people fully perceive the world around them and enjoy sounds and communication with loved ones.

As you can see, a DIY hearing aid quite easy to do, there is nothing complicated about it, but the benefits are quite tangible.

It does not heat up, therefore there is no need for a heat sink. I advise you to use capacitors and resistors in the SMD version, which will significantly reduce the size of the hearing aid. The microphone, as in the first article, is used from a mobile phone headset (it is convenient due to its small size), but if you don’t have one, use any electret microphone. The power source can be a lithium tablet or watch batteries.

But since here we have not just a microphone amplifier as in our first article, but an integrated amplification microcircuit, therefore the current consumption is significantly higher - up to 20 mA, which means it would be advisable to use a lithium-ion battery from a Bluetooth headset of a mobile phone. The power supply capacitor can be excluded from the circuit; it does not play a special role. The hearing aid amplifier can be assembled on a breadboard along with a battery and placed in a suitable headset housing. You can make the case yourself from plastic cards and glue it with silicone.

As you noticed in the photo there is no amplifier volume control; without a volume control, the amplifier operates at full power; if desired, the design can be supplemented with a variable resistor to adjust the sound. If you use a battery, be sure to include a charging socket. The device can be charged using an ordinary charger from a mobile phone, or a USB port, but the best option is charging with a universal charger, since there is a controller and a charging current limiter, and this will increase the life of the battery. That's all, good luck friends - AKA.

A hearing aid is a simple sound amplification device consisting of a microphone, an input amplifier, a final amplifier and a telephone. The input amplifier is assembled on two transistors T1 and T2 according to a circuit with direct connections between the stages and is covered by a common negative DC feedback in order to stabilize the gain and improve the amplitude-frequency characteristics. Setting the modes of transistors T1 and T2 is carried out using resistors R3 and R6. It is important to use the low-noise transistor P28 in the first stage of the amplifier. In addition, the operating mode of this transistor (Ik = 0.4 mA, Uke = 1.2 V) also ensures minimal noise. The amplifier provides uniform signal amplification in the frequency band of the conversational spectrum 300...7000 Hz. From the collector of transistor T2, the signal goes to potentiometer R7, which acts as a gain regulator. Instead of the P28 transistor, you can use: MP39B, GT310B, GT322A, silicon KT104B, KT203B, KT326B, but low-noise transistors of the KT342, KT3102 and KT3107 series give especially good results. The final stage is assembled on transistor T3 according to an amplifier circuit with a floating operating point, which makes it possible to sharply reduce the current consumed by the stage in silent mode.

This hearing aid amplifier circuit is characterized by an effective shift of the cascade operating point and, accordingly, small nonlinear distortions. When a signal is applied to the input from resistor R7 through capacitor C6, the signal is sent to the base of transistor T3. The signal amplified by the transistor from the collector T3 through capacitor C8 is sent to a doubler rectifier on diodes D1 and D2. The rectified voltage accumulates on capacitor C7 and is applied to the base of transistor T3, shifting its operating point towards opening.

Resistor R8 sets the initial cascade current. The hearing aid is powered by a voltage of 9 volts from the Krona element. LED D3 serves to indicate power on. Any miniature dynamic or condenser microphone can be used as a microphone. If you are using a condenser microphone, you must supply power to it through a 3–5 kOhm resistor. You can use TM-3, TM-4 as a telephone. A suitable plastic case was selected for the hearing aid, which houses the printed circuit board and power supply. When setting up, you must first set the currents of all transistors. resistors R4 and R6 current T1 and T2, then resistor R8 with the microphone turned off, set the quiescent current of Transistor T3 to 2-2.5 mA. A signal with a frequency of 1000 Hz and an amplitude corresponding to the maximum signal amplitude at the collector of transistor T3 is supplied to the base of transistor T3 from the generator. Use resistor R9 to achieve undistorted signal amplification. In this case, the collector current of the transistor should have a value of 15-17 mA. Select the capacitance of capacitor C3 according to the best sound, the absence of harsh sounds. Author: Shimko Sergey.

The hearing aid functionally consists of a highly sensitive electret microphone and a low-noise low-frequency amplifier (LFA), loaded onto headphones (see figure).

The hearing aid amplifier must have a gain of more than 10,000 times the voltage, increase the frequency response in the range of 300-300 Hz and provide sufficient output power. Low-voltage power supply (2-3 V) forces you to carefully consider the selection of power modes based on the direct current of the transistors, the quality of the transistors themselves and other parts. Despite the reduced power supply, the problem of dealing with amplifier excitations at both audio and high frequencies remains.

Details and design. The housing under the Chinese VHF micro-receiver contains headphones, a socket for connecting them, a volume control with a switch, and a power-on LED.

When designing a printed circuit board, it is necessary to place these parts so that they coincide with the holes present in the body of the former receiver. Naturally, this design option for a hearing aid is not the only one.

Details. Small-sized electret microphone

MKE-ZZ2; transistors KT3102D, E with gain 500-800, KT31 5b, G, E with gain 100-150; resistors type MLT-0.125; capacitors of various types, the main requirement for them is as small as possible. Headphones are small-sized headphones made in China. Power supply is from galvanic elements. The current consumed by the hearing aid is almost 2 times less than that of VHF microreceivers.

The setup consists of selecting resistor R1 within the specified limits for the maximum sensitivity of the device. The maximum current consumption with fresh batteries is 9-10 mA. Evidence of a properly tuned ULF is that it remains operational at a supply voltage of 1.5 V, although the gain is significantly reduced compared to power supply from two elements.

This hearing aid has a lower noise level than hearing aids produced in the Soviet Union in the 80s; Its sensitivity and output sound pressure level are higher than those of behind-the-ear hearing aids or glasses placed in the earpiece.

The circuit of a hearing aid can be considered as basic. Although the design takes some measures to narrow the frequency band, its sound is much more natural and pleasant than that of industrial hearing aids.

parathas. However, further narrowing of the ULF frequency band may be necessary when designing devices for people with severe hearing loss.

To reduce current consumption, a “floating point” mode, etc., can be introduced into the final stage of the ULF.

Literature: 1. Amateur Radio Handbook/Ed. G.M. Tereshchuk, K.M. Tereshchuk, S.A. Sedo-va.-K.: Vishcha school, 1981.

Today we will make a hearing aid. The video will consist of two parts. In this one I will describe the electrical part, and in this one I will describe the manufacture of the case and installation of electronics into it.

A little background

My grandfather is entering his ninth decade. Over time, he became hard of hearing. For a couple of years he used a miniature BTE hearing aid from Siemens. Until I successfully lost it. It would seem that they bought a new one and forgot about the problem, but I decided to get confused and make a homemade one. There are several reasons for this decision. Firstly, the price issue. As the dollar has risen, hearing aids have increased in price significantly. Secondly, the mentioned specimen had an extremely short operating time on button batteries. They had to be changed once or twice a week. Thirdly, wearing a headdress caused extraneous noise that made it difficult to hear the conversation. Fourthly, the monoblock design and close proximity of the speaker and microphone caused constant squeaks at maximum volume, but nothing was audible at an average sound level. Therefore, I decided to kill all the birds with one stone and make a device using AAA batteries, consisting of several blocks.
The earphone and microphone will be located according to the principle of a wired headset. And the case, which will contain batteries and a printed circuit board, will be carried in a trouser pocket or on a belt. It will have to perform the function of the screen and protect the internal elements from damage due to accidental falls or steps on it.

Hearing aid diagram

I looked up the circuit design on the radioskot website http://radioskot.ru/publ/unch/karmannyj_slukhovoj_apparat/6-1-0-627 The circuit is quite confusing. I tried to simplify it.

The main amplifier is a Motorola MC34119 microcircuit. Let's take a look at the datasheet. The mikruha consists of 45 transistors and can operate on 2V, for example from 2 NiMH batteries, which, when completely discharged, will have a voltage of 1V each, i.e. the total amount we need is 2V. At the same time, the microcircuit consumes extremely little. 2.7 mA stated. And it can deliver up to 250 mW of power per 32-ohm headphone. Quite good indicators.

The simplest inclusion option has minimal weight. But I, like the author of the mentioned circuit, realized during experiments on a breadboard that it is best to use the option with suppression of high-frequency sounds.

I empirically selected an electret microphone from an old Philips phone based on sound quality; it turned out to be noticeably better than other microphones.

My version

I managed . (KiCAD project file) A few words about the preamplifier. Because I didn’t have the preamplifier parts indicated on the diagram, so I decided to experiment with what I had. And in stock I had the banal KT315B. During the experiments, it turned out that the very first option with just one transistor turned out to be the most successful, and all subsequent ones had poor sound quality and poor amplification. But at the same time, if a common power supply was applied to the microphone and the preamplifier, the preamplifier began to self-excite. All my attempts to solve this problem only led to worse sound. In the end, after weighing all the pros and cons, I decided that the elegance of the technical solution had less priority over the sound, and used a second battery pack to power the preamplifier. Yes, my weight and dimensions have increased, but I am making the first experimental sample and this is forgivable. This is the compromise.

The circuit also contains another transistor - BC547, which switches the amplifier chip to a low-power mode when the supply voltage drops below 2.0V. This prevents the main batteries from being completely discharged. This doesn’t work with preamplifier batteries, and although this issue could have been solved, I decided that it was not so critical. Because Measurements of current consumption showed that the preamplifier consumes 10 times less current, namely 0.6 mA and 6.3 mA, respectively. Taking this into account, we can make the assumption that the preamplifier batteries will be charged once every ten charges of the main batteries, which is quite acceptable. Having a main battery capacity of 1000 mAh, we have about 160 hours of continuous operation. We can make the assumption that this charge will be enough for 2-3 weeks of work for 8-10 hours a day. Which is quite a good indicator. The circuit also contains a volume control that regulates the voltage on the electret microphone.

Signet

Everything according to the plan. Let's move on to the seal. Because I initially assembled the parts on a breadboard, I decided to rearrange them on the board without any problems, so our board is THT - pin mounting - much more convenient for experimental things. It is quite possible that there will be an SMD option later. The board was laid out in the KiCAD program, then exported to SVG and printed from a vector editor. I used single-sided fiberglass. The drawing was translated using the LLT method. Those. I printed on photo paper using a laser printer, and warmed it up using a laminator. Initially I tried to separate the paper using isopropyl alcohol - I always used this option with thermal transfer paper, but then I failed. The second time I used soaking in water, I cleaned off the remaining film with a toothbrush and toothpaste. It turned out very well. Etched in ferric chloride. Covered with Rose alloy in boiling water. I drilled with a machine using a microscope. There were no particular problems with the installation, but as always, I messed up with the mirror image, so the mikruhi’s legs had to be turned inside out.

In the next episode