Is it possible to make a hearing aid with your own hands. DIY Hearing Aid Hearing Aid Preamplifier Circuit
The hearing aid is a simple sound amplifying device consisting of a microphone, an input amplifier, a power amplifier and a telephone. The input amplifier is assembled on two transistors T1 and T2 according to a circuit with direct connections between the cascades and is covered by a common negative DC feedback in order to stabilize the gain and improve the frequency response. 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 operation mode of this transistor (Ik=0.4 mA, Uke=1.2 V) also provides 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 is fed to the 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 the T3 transistor according to the floating operating point amplifier circuit, which makes it possible to drastically reduce the current consumed by the stage in silent mode.
This hearing aid amplifier circuit is characterized by an effective shift of the operating point of the cascade and, accordingly, small non-linear distortions. When a signal is applied to the input from the resistor R7 through the capacitor C6, the signal enters the base of the transistor T3. The signal amplified by the transistor from the collector T3 through the capacitor C8 is fed to the rectifier-doubler on diodes D1 and D2. The rectified voltage is accumulated on the capacitor C7 and applied to the base of the transistor T3, shifting its operating point towards opening.
Resistor R8 sets the initial current of the cascade. 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. In the case of using a condenser microphone, it is necessary to supply power to it through a 3-5 kΩ resistor. As a phone, you can use TM-3, TM-4. A suitable plastic case was selected for the hearing aid, which houses the printed circuit board and the power supply. When establishing, it is necessary first of all to set the currents of all transistors. resistors R4 and R6 currents 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 amplitude of the signal at the collector of transistor T3 is supplied to the base of the transistor T3 from the generator. 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 the capacitor C3 according to the best sound, the absence of sharp sounds. Author: Shimko Sergey.
V. Muravin
Hearing aids (HA) help people with hearing loss to communicate with the outside world, take an active part in work and social activities. For some, it is the only way to reproduce human speech, for others it is a means of increasing speech intelligibility and even makes it possible to improve the quality of listening to music.
In our country, the industry produces several types of hearing aids with different technical characteristics and in different designs.
Currently, work is underway to transfer hearing aids to a new element base, to improve their technical characteristics and operational conveniences. So, a specialized microcircuit for SA K538UN2 has been developed. The amplifier of this chip has low noise, power consumption and is designed to connect a phone with a resistance of 1 kOhm.
However, industrially produced SAs have the following disadvantages:
insufficient acoustic amplification. Hearing loss in people with damage to the sound reproducing apparatus can reach 80 ... 90 dB at a frequency of 4 kHz, which is considered the minimum acceptable upper passband frequency in terms of ensuring satisfactory (92%) speech intelligibility;
flat frequency response of the device, which, according to GOST 10893-69, should have an unevenness of not more than 30 dB in the frequency band of 400 ... 3000 Hz (people with different types of hearing loss have different audiograms);
low cost efficiency. Consumption currents have a strength of about 5 ... 12 mA, which, when using power supplies with a capacity of 0.05 ... 0.15 mA / h, ensures the operation of the device for 10 ... 12 hours. linear mode, and this leads to the fact that the current consumption in silent mode is the same as at maximum volume;
lack of limiters of the maximum level. Only one SA model has AGC, which is also ineffective. Peak limiters and compressors are not used in industrial hearing aids;
the absence of noticeable (clearly visible) turn-on indicators, which is especially important at relatively high consumption currents. As a rule, the CA has a mark on the volume control, combined with the power switch.
Among the SA parameters, the amplitude-frequency response (AFC) of the hearing aid and the noise level have the greatest influence on the quality of sound reproduction and speech intelligibility, and, consequently, on the real effect in hearing prosthetics.
Let's dwell on this in more detail. As already noted, commercially available hearing aids have a poor frequency response, and hearing loss can be characterized by various audiograms. If, with damage to the sound-reproducing apparatus, the audiogram is flat and has an unevenness of about 20 dB, then with damage to the sound-perceiving apparatus and combined damage, the audiogram has a decline in the frequency range of 500 ... 4000 Hz with a slope reaching 30 dB / oct. .
In addition, it should be taken into account that microphones and telephones used in SA also have a drop in the frequency response with a slope reaching 30 dB/oct in the frequency range of 2000...4000 Hz. Some CAs are equipped with frequency response controls, but these are the simplest circuits and do not provide the required correction.
The second important factor influencing the quality of the SA is the noise level. It is known that for intelligible speech perception it is necessary that a signal-to-noise ratio of more than 20 dB is observed. If we take the minimum sound intensity level of 40 dB, then the voltage of the noise brought to the input should be no more than 3 μV.
The internal noise of the SA can be reduced by using low-noise transistors in the input stages.
It is more difficult to isolate the useful signal against the background of surrounding noise. If a healthy ear perceives ambient noise selectively in direction, that is, it selects useful information from them coming from a certain direction, then SA amplifies sounds coming from all directions; as a result, the signal-to-noise ratio at the entrance of the auditory canal is insufficient.
When improving SA and creating new models, it is necessary to take into account all of the above factors that affect the quality of sound reproduction and speech intelligibility.
Consider the block diagram of the hearing aid.
A hearing aid is, as a rule, a device consisting of a microphone, an input amplifier, a correction device, a final amplifier, and a telephone (Fig. 1).
Rice. 1 Hearing aid block diagram
The correction device can be combined with one of the amplifiers, however, it will not be functionally and structurally complete and fully meet the rather high requirements for correcting the frequency response of the SA.
In addition, the CA can additionally include a limiter for the maximum output level, an indicator for turning on the CA, an indicator for low batteries, etc.
The technical requirements for both the entire hearing aid and its constituent devices are determined by the characteristics of the patient's hearing.
The most detailed and accurate measurement of hearing characteristics is provided by the audiometric method of measurement, in which tones of various frequencies and loudness are applied to the ear under examination through electrodynamic telephones. Electrodynamic phones are suitable in this case, since they have the lowest acoustic impedance and therefore provide less dependence of sound pressure on individual differences in the size of the outer ear. In addition, this satisfies the requirement of uniformity of measurements, when the results can be compared and do not depend on the place, time and conditions of the performance.
You can go the other way: take an audiogram with the phone that will be used with the hearing aid. Then the audiogram will take into account both the frequency characteristics of this phone and the individual characteristics of the ear canal, which will allow you to create a more effective scheme for correcting the frequency response of the hearing aid. The second way is acceptable when creating SA for a particular patient. In the event that CAs are created on a modular basis, a number of correction device modules can be developed, one of which, after taking an audiogram, is built into the device.
Input amplifier CA must have a gain sufficient to drive the final stage. Low noise is also an important requirement, since the signal source for the input amplifier is a microphone with a relatively low sensitivity (about 4 mV/Pa). A feature of the operation of the input amplifiers SA are low operating currents and voltages.
Typically, CA input amplifiers are built according to a two- or three-stage circuit, in which transistors are switched on according to a common emitter circuit. Stabilization of the DC mode is carried out with the help of local negative feedbacks.
Greater stability than in industrial SA, has an amplifier, the circuit of which is shown in Fig. 2.
Rice. 2. Schematic diagram of the input amplifier 1
This amplifier is built according to a circuit with direct connections between the stages and is covered by a common negative feedback (CNF) for direct current. The DC mode is set using resistors R3 and R6. In the first stage of the amplifier, a low-noise transistor P28 is used. In addition, the operation mode of this transistor (Ik=0.4 mA, Uke=1.2 V) also provides minimal noise. The frequency band of the amplifier at the level of -3 dB is 300 ... 7000 Hz, the gain coefficient Ku is 1700.
In low-noise input stages, germanium transistors P28, MP39B, GT310B, GT322A, silicon KT104B, KT203B, KT326B work well, but low-noise transistors of the KT342, KT3102 and KT3107 series give especially good results. They are capable of operating at collector currents of tens of microamperes and collector-emitter voltages of less than 1 V without losing high amplifying properties.
The circuit of the input amplifier on KT3102E transistors is shown in fig. 3 and is similar in construction to the previous scheme.
Rice. 3. Schematic diagram of the input amplifier 2
The transistor of the first stage operates in microcurrent mode (Ik = 0.04 mA, Uke = 1 V). The gain of such an amplifier is 3000.
More gain can be obtained if an emitter follower is placed between the first and second stages as shown in Fig. 4.
Rice. 4. Schematic diagram of the input amplifier 3
Here, in addition to local negative feedbacks in each stage and the general DC OOS, an AC OOS (Ros) is also introduced, with which you can adjust the gain of the amplifier. The gain of the amplifier without feedback (Ros disabled) is 11,000, with feedback - 1700; noise voltage brought to the input when it is shorted, no more than 2 μV.
It was already mentioned earlier that the main distortions of the end-to-end frequency response of the SA are determined by the microphone and the telephone. The most common microphone in hearing aids is the M1. Its frequency response is shown in fig. 5 .
Rice. 5. Frequency response of the microphone
This characteristic is averaged and taken in a free sound field. Such measurements represent a difficult technical problem. In real conditions, the type of frequency response of a microphone is greatly influenced by the volume of the room, surrounding objects, etc. Therefore, in the future, we will take into account the average response of the microphone.
Analysis of the average characteristics of a microphone, telephone and hearing loss in various types of damage allows us to divide the frequency range into three sections: up to 1000 Hz, from 1000 to 2000 Hz and above 2000 Hz.
In the area up to 1000 Hz, the resulting frequency response, which is the sum of the frequency response of the microphone, phone and hearing loss, has a slight rise due to the rise in the frequency response of the microphone and phone.
In the area from 1000 to 2000 Hz, the resulting frequency response can be constant, have an increase or decrease, which is associated with the shape of the hearing loss characteristic in this area. There can also be small highs and lows.
At frequencies above 2000 Hz, the drop in the resulting frequency response is due to the drop in the phone's frequency response and hearing loss characteristics.
Hence it follows that when developing correction devices, it is necessary to form the frequency response of these devices, the inverse of the resulting frequency response of the "microphone-phone-ear" path.
Such a correction characteristic can be obtained by connecting low-pass filters (LPF), high-pass filters (HPF) or trap filters in parallel in various combinations. The number of filter sections depends on the desired frequency response slope.
Correction devices can be built on the basis of active filters described in, in which it is better to use not operational amplifiers, but more economical emitter followers as non-inverting amplifiers.
Rice. Fig. 6. Schematic diagrams of filters of the second order: a - low frequencies; b - high frequencies
Schemes of active HPF and LPF of the second order are shown in fig. 6, and HPF and LPF of the third order - in fig. 7. They have frequency responses with a slope of 12 and 18 dB/oct. respectively.
Rice. Fig. 7. Schematic diagrams of the filter of the third order: a - low frequencies; b - high frequencies
If the correction characteristic should have a larger slope, several filters must be connected in series.
The scheme of the barrier filter is shown in fig. 8, a, and its frequency response - in fig. 8, b.
Rice. 8. Barrier filter:
a - schematic diagram; b - frequency response
The stopband of a filter depends on its gain.
The average frequency of the stopband is determined by the formula
fo=0.28/RC,
where R=R1=R2, C=C1=C2.
Final amplifiers should have, as a rule, a flat frequency response, provide the required maximum signal level at the load and be economical.
In industrial SAs, the final stage is usually built according to a single-cycle circuit and operates in a linear mode, so the output level and efficiency of such amplifiers, and, consequently, the SA, are low.
It is possible to increase the efficiency of the SA if the final amplifier is built according to the floating operating point scheme, as shown in Fig. 9a, b).
Rice. 9. Schematic diagrams of terminal amplifiers with a floating operating point
The device according to the scheme in fig. 9b is distinguished by a more efficient shift of the operating point of the cascade when a signal is applied to the input and, accordingly, lower non-linear distortions. Resistor R1 sets the initial current (without signal) equal to 2 ... 3 mA, and resistor R2 sets the minimum signal distortion at the load. In this case, the maximum collector current of the transistor VT1 reaches 20 mA. The final amplifier built according to the scheme of fig. 9, provides a maximum signal of 500 mV at a 3 V supply voltage and 1.5 mV at a voltage of 9 V into a 60 Ω load, which corresponds to maximum output levels of 120 and 130 dB (with a phone sensitivity taken as 0.04 Pa/mV). The disadvantages of such circuits are low (no more than 10 ... 15%) efficiency and large non-linear distortions. Higher efficiency (up to 50%) is provided by final amplifiers built according to a push-pull circuit, as shown in Fig. 10, a, b. In these amplifiers, the initial current, equal to 1.2 mA for the circuit of Fig. 10, a and 2 mA for the circuit of fig. 10, b, is set by resistors R4 and R2, respectively. Resistors R2 and R4 for circuits according to fig. 10, a and 10, b, respectively, the voltage is set at point A, equal to half the supply voltage.
Figure 10. Schematic diagrams of push-pull power amplifiers
Terminal amplifiers built according to the circuits of Fig. 10 provide maximum output levels of 122 and 133 dB for fig. 10, a and 10, b, respectively, the efficiency is about 50%.
Almost the same characteristics as the amplifier built according to the circuit of Fig. 10, b, but with a smaller number of parts, has an amplifier based on the K140UD5A operational amplifier (Fig. 11). Here, resistor R1 sets the voltage at point A, equal to half the supply voltage, and resistor R4 sets the stage gain. The initial current is approximately 2.8 mA. The amplifier built according to the scheme of fig. 11 provides a maximum output level of 131 dB. The efficiency of this amplifier is somewhat lower than that of the previous ones - 37%.
During the study, the goal was not to select transistors in each pair according to the h21e parameter. When selecting transistors for each pair, their reference data were considered: structure (p-n-p, n-p-n), material (germanium, silicon), collector reverse current, gain, saturation voltages. The transistors were installed in an amplifier made according to the scheme of Fig. eleven.
Rice. 11. Schematic diagram of the final amplifier with a microcircuit
In each pair, 3 transistors of each type were examined (to exclude random selection). The maximum output voltage was measured at the load - a resistor with a resistance of 60 ohms. The measurement results are given in table. 1.
The table shows that the best results are obtained with germanium transistors. The use of high-frequency transistors GT329B and GT310B is not justified, moreover, the values of the maximum permissible parameters of these transistors are close to the operating mode in this amplifier.
Even greater efficiency (up to 75%) have end-of-line amplifiers made according to the bridge circuit. Although they have almost 2 times more parts, they allow you to get twice as much power at the same power supply voltage, which is especially important for portable devices.
In the simplest case, the final amplifier, assembled according to the bridge circuit, consists of two identical terminal stages (A2, A3), the inputs of which are connected to a stage with two-phase outputs (A1), and the outputs are connected to the load (Fig. 12).
Rice. 12. Structural diagram of the bridge terminal amplifier
When using integrated operational amplifiers (op-amps) in the final stages, you can exclude a stage with two-phase outputs by turning on one op-amp according to the circuit with an inverting input, the other according to the circuit with a non-inverting input. The scheme of such an amplifier is shown in fig. 13.
Rice. 13. Schematic diagram of the bridge final amplifier
Final amplifiers can also be made according to the diagrams given in. All of them are assembled in a bridge circuit and differ from each other in the way the output transistors are turned on and driven. The efficiency of these amplifiers is from 40 to 75%.
In table. 2 shows the comparative characteristics of the final amplifiers, made according to the schemes of fig. 9, 10, 11, 13.
table 2
In industrial SAs, the indication of the on state is carried out using the risks on the volume control, combined with the power switch.
However, such an indicator is hardly noticeable, and idling leads to a rapid discharge of power supplies.
A good indication of the inclusion of the SA is provided by the LEDs. Practice has shown that the AL102A LED glows well already at a current of 2.5 ... 3 mA, and the AL310A LED - even at a current of 1.5 mA.
To indicate the inclusion of SA, you can use a pulse indicator, the diagram of which is shown in fig. 14. It is based on an asymmetric multivibrator on transistors VT1, VT2. The load of the multivibrator is the VD3 AL310A LED. The duration of its glow is determined by the parameters of the R2C1 circuit, and the flash frequency is determined by the parameters of the R3C2 circuit. Resistor R4 limits the pulsed current through the LED. In the above diagram, the LED flash rate is approximately 0.5 Hz, and the ratio of the off to on state of the LED is about 7.
Rice. 14. Schematic diagram of a pulse indicator
Let's consider several possible SA designs.
The diagram of the simplest SA is shown in fig. 15 . This apparatus includes a two-stage input amplifier and a single-stage floating-point output amplifier. The indicator of inclusion is the LED AL102A.
Rice. 15. Schematic diagram of the hearing aid 1
The device uses a Ml microphone and a TM2A telephone from industrial hearing aids. Volume control with switch - resistor SP3-3. The device is powered by a Krona battery.
Specifications SA: acoustic gain 58 dB, maximum output level 128 dB. Initial current consumption (without signal) no more than 4 mA. The frequency response of the amplifier is flat in the range of 300...7000 Hz. SA is placed in a plastic case measuring 85X59X24 mm.
Hearing aid, the scheme of which is shown in fig. 16 is quite economical: when powered by two 1.5 V batteries, it consumes (in the absence of a signal) a current of 1.7 mA. At the same time, the SA parameters are not worse than those of the previous design. Thus, the acoustic gain is 64 dB, and the maximum output level is 120 dB. This SA also has a flat frequency response in the range of 300...6000 Hz and is housed in a plastic case measuring 85x59x18 mm.
Rice. 16. Schematic diagram of the hearing aid 2
When developing the next design, the characteristics of hearing loss with the TM-2A telephone were taken. The audiogram of a hearing-impaired person was compared with that of a healthy person. The difference between these two audiograms is the characteristic of hearing loss, which is shown in Fig. 17.
Rice. 17. Characteristics of hearing loss
The audiogram was taken as follows. First, the frequency and the minimum signal level from the generator output were set. Then the phone, for which the developed device is designed, was placed in the ear canal. The signal level was gradually increased until it became audible. The signal from the generator output was measured. Then the normally audible signal was gradually reduced. When the sound in the phone disappeared, the signal from the output of the generator was measured with a millivoltmeter. The arithmetic mean of the first and second measurements of the generator signal will be the threshold level. It is necessary to measure the threshold levels in the frequency range 200...7000 Hz. To improve the accuracy of measurements and eliminate random errors, audiogram recording can be repeated 3...5 times.
It can be seen from the loss characteristic that in the section up to 1000 Hz there is an increase with a slope of approximately 12 dB/oct., and after 1000 Hz there is a sharp decline: up to 2500 Hz with a slope of 26 dB/oct., then even more. By superimposing the average frequency response of the microphone on the hearing loss characteristic, we can obtain the characteristic of the correction device. It looks like it is shown in fig. 18.
Rice. 18. Characteristics of the correction device
Such a characteristic can be obtained using a trap filter, the circuit and experimental frequency response of which is shown in Fig. 19.
Rice. 19. Schematic diagram and frequency response of the surge filter
Diagram of a hearing aid with correction is shown in fig. 20.
Rice. 20. Schematic diagram of the hearing aid 3
This device contains a two-stage input amplifier, a correction device, which is a trap filter, a two-stage terminal amplifier, assembled according to a two-cycle transformerless circuit, and a pulsed indicator for switching on the SA. Acoustic amplification of the device is 87 dB, the maximum output level is 124 dB. Initial current consumption (without signal) no more than 1.8 mA. The flashing frequency of the LED indicator is chosen to be approximately 0.5 Hz, and the ratio of the off and on states of the LED is about 7, so its consumption from the power source is low.
The hearing aid is powered by two 1.5 V batteries. It is housed in a plastic case measuring 59x85x16 mm. According to the subjective assessment, these speakers provide good speech intelligibility and improve the quality of listening to music. A particularly large gain was obtained in the area of 1...3 kHz, while when using conventional hearing aids, sounds with such frequencies are practically not heard.
Literature
1. Ephrussi M. M. Hearing aids and audiometers.- M .: Energy, 1975.
2. Muravy and VD Hearing aids.- To help the radio amateur. Issue. 58, 1977.
3. Alekseev G. V. Some methods of connecting bridge power amplifiers to a preamplifier. - Semiconductor electronics in communication technology. Issue. 21, 1981.
4. Maklyukov M. RC filters with flat frequency characteristics. Radio, 1968, No. 7.
5. Kareev V., Terekhov S. Operational amplifiers in active RC filters. - Radio, 1977, No. 8.
[email protected]
Yu. A. Shtan, V. Yu. Shtan, Berdyansk
functionally consists of a highly sensitive electret microphone and a low-noise low-frequency amplifier (ULF) loaded on headphones (see figure).
The hearing aid amplifier must have a gain of more than 10,000 times the voltage, a boost in the frequency response in the range of 300-300 Hz, and provide sufficient power at the output. Low-voltage power supply (2-3 V) forces you to carefully consider the selection of power supply modes for the direct current of transistors, the quality of the transistors themselves and other details. Despite the reduced power supply, the problem of dealing with amplifier excitations both in audio and high frequencies remains.
Details and design. Headphones, a socket for their connection, a volume control with a switch, and a power-on LED are placed in the case from under the Chinese VHF micro-receiver.
When designing a printed circuit board, it is necessary to place these parts in such a way that they coincide with the holes available in the case of the former receiver. Naturally, this version of the design of the hearing aid is not the only one.
Details. Microphone small electret
FEM-332; transistors KT3102D, E with a gain of 500-800, KT31 5b, G, E with a gain of 100-150; resistors type MLT-0.125; capacitors of various types, the main requirement for them is possibly smaller sizes. Headphones - small-sized head phones made in China. Power supply - from galvanic cells. The current consumed by the hearing aid is almost 2 times less than that of VHF microreceivers.
The adjustment consists in the selection of the resistor R1 within the specified limits according to the maximum sensitivity of the apparatus. The maximum current consumption with fresh batteries is 9-10 mA. Evidence of a properly debugged ULF is the preservation of its performance at a supply voltage of 1.5 V, although the gain is significantly reduced compared to a power supply from two elements.
This hearing aid has a lower noise level than hearing aids produced in the Soviet Union in the 80s; the sensitivity and sound pressure level at the output is higher than that of hearing aids behind the ear or placed in the arm of glasses.
The circuit of the hearing aid can be considered as basic. Although the circuit has taken some steps to narrow the bandwidth, it sounds much more natural and pleasant than industrial hearing aids.
paraty. However, further narrowing of the ULF frequency band may be necessary when designing devices for people with a high level of hearing loss.
To reduce the current consumption, the “floating point” mode, etc., can be introduced into the final stage of the ULF. Literature
1. Handbook of a radio amateur / Ed. G.M. Tereshchuk, K.M. Tereshchuk, S.A. Sedo-va.-K.: Vishcha school, 1981.
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Good day dear colleagues. We continue the section of medical equipment. In the previous article, we talked about how to make it simple for the elderly from improvised materials and using just a few details. Today I bring to your attention the modernization of such a device, or rather not modernization, but a completely new version using an integrated amplifying microcircuit TDA2822M. The microcircuit has only eight outputs and it is a high-quality low frequency amplifier, inside it has two channels of 0.65 watts each. The supply voltage range is also very wide - from 1.5 to 18 volts. Such an amplifier is also found in the smd version, it can be found in the player, radio, and so on. You can of course buy just in the radio store. Assemble the amplifier according to the bridge option, which will allow you to get up to 1.5 watts of pure power. See the diagram below for turning on the hearing aid.Does not heat up, hence the need for heat dissipation is eliminated. I advise you to use capacitors and resistors also in 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 for its small size), but if there is none, 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 amplifying microcircuit, therefore, a significantly higher current consumption - up to 20 mA, which means it would be advisable to use a lithium-ion battery from the bluetooth headset of a mobile phone. The power 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 the battery and placed in a suitable headset case. The case can be made by yourself from plastic cards and glued 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, you can supplement the design with a variable resistor to adjust the sound. If you are using a rechargeable battery, be sure to include a charging socket. The device can be charged using an ordinary mobile phone charger or usb port, but the best option is to charge it 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.
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