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    This is a less expensive, and DIY option for a hearing aid. It is not a substitute for a real hearing aid that an audiologist would prescribe. Amplification of all sounds and frequencies, or constant use in loud environments can cause additional hearing loss. This circuit could be helpful for some types of hearing loss and occasional use, as well as fill in during the average amount of time people wait to get a hearing aid (7 years).

    This low-cost, general-purpose electronic circuit works off 3V DC (2×1.5V battery). Transistor T1 and associated components form the audio signal preamplifier for the acoustic signals picked up by the condenser microphone and converted into corresponding electrical signals.

    Application

    Medical grade hearing aids are very expensive, if a person needs help hearing but not necessarily the full cost and capability of a prescribed hearing aid, this might be an option.

    The medium-power amplifier section is wired around popular audio amplifier IC TDA2822M (not TDA2822). This IC, specially designed for portable low-power applications, is readily available in 8-pin mini DIP package. Here the IC is wired in bridge configuration to drive the 32-ohm general-purpose monophonic earphone.

    The audio output of this aid circuit is 10 to 15 mW and the quiescent current drain is below 1 mA. The circuit can be easily assembled on a veroboard. For easy assembling and maintenance, use an 8-pin DIP IC socket for TDA2822M.

    Schematic of Hearing Aid Circuit

    hearing aid circuit schematic

    Click here for parts list

    RefDes Name Value Part Number Digi-Key Part Number Description
    R1 RESISTOR 2.2K 6-1676481-2 A103077CT-ND RES 2.20K OHM 1/16W 0.1% 0603
    R2 RESISTOR 330K ERJ-3GEYJ334V P330KGCT-ND RES 330K OHM 1/10W 5% 0603 SMD
    R3 RESISTOR 680 ERJ-3GEYJ681V P680GCT-ND RES 680 OHM 1/10W 5% 0603 SMD
    R4 RESISTOR 33 ERJ-3GEYJ330V P33GCT-ND RES 33 OHM 1/10W 5% 0603 SMD
    C1 NON POLARIZED 0.01uF C0603X5R1A103K030BA 445-1793-1-ND CAP CER 10000PF 10V 10% X5R 0201
    Q1 NPN BC547 BC547CTA BC547CTACT-ND TRANSISTOR NPN 45V 100MA TO-92
    C2 NON POLARIZED 0.1uF LDEEC3100KA5N00 399-5480-1-ND CAP FILM 0.1UF 100VDC 1812
    C3 POLARIZED 47uF 450-1598-ND 450-1598-ND 450-1598-ND
    R5 RESISTOR 100 ERJ-3GEYJ101V P100GCT-ND RES 100 OHM 1/10W 5% 0603 SMD
    R6 VARIABLE 10K EVM-3YSX50B14 P3Y103CT-ND TRIMMER 10K OHM 0.15W SMD
    C4 POLARIZED 10uF EEE-1AA100NR EEE-1AA100NR CAP ALUM 10UF 10V 20% SMD
    C5 NON POLARIZED 0.01uF C0603X5R1A103K030BA 445-1793-1-ND CAP CER 10000PF 10V 10% X5R 0201
    U1 AMPLIFIER   TDA2822M 497-8863-5-ND IC AMP AUDIO DUAL LOW VOLT 8MDIP
    C6 POLARIZED 100uF EEE-1AA101WR EEE-1AA101WR CAP ALUM 100UF 10V 20% SMD
    R7 RESISTOR 4.7 ERJ-3GEYJ4R7V P4.7GCT-ND RES 4.7 OHM 1/10W 5% 0603 SMD
    R8 RESISTOR 4.7 ERJ-3GEYJ4R7V P4.7GCT-ND RES 4.7 OHM 1/10W 5% 0603 SMD
    C7 NON POLARIZED 0.1uF LDEEC3100KA5N00 399-5480-1-ND CAP FILM 0.1UF 100VDC 1812
    C8 NON POLARIZED 0.1uF LDEEC3100KA5N00 399-5480-1-ND CAP FILM 0.1UF 100VDC 1812
    SPK1 SPEAKER        
    R9 RESISTOR 220 ERJ-3GEYJ221V P220GCT-ND RES 220 OHM 1/10W 5% 0603 SMD
    L1 LED   VLMTG1300-GS08 VLMTG1300-GS08 LED TRUE GREEN 0603 SMD
    S1 SPST   SLS121PC04 SLS121PC04 SLS121PC04
    MIK1 MICROPHONE   TOM-1545P-R TOM-1545P-R MIC COND ANALOG OMNI -45DB
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    38 Responses to "Hearing Aids Circuit"

    1. Interesting project..
      Seems futurustic and portable :)

    2. It’s an analog device not digital and takes 6mA minimum!!! Not a lot of use.

    3. where’s the digital?

    4. sucks

    5. can anybody tell me what is the idea of that dotted line from on/off switch to VR1 varialble resistor??

      • friend:oftenly u would have been using a old radio model,when u do its volume lower and more lower after this there is a stage when volume sounds click and device gets off same this function is applied here

      • Rene Gregorio says: on August 21, 2012 at 6:12 pm

        The dotted line indicates that the on off switch is part of VR1 variable resistor which is also the volume control.

    6. the on/off switch is joined to the vr1 to indicate that it is a switch pot. The volume control and and on/off switch are the same device

    7. This circuit gives excellent sound clarity.It is truly compact and portable.Omitting the LED indicator will decrease the current consumption.The design is analog.However it can cope with digital aids when it comes to sound reception and reproduction.

    8. How we can modify the circuit to make it work like digital. If anyone tested the sound and working of this project, any feedback or humming noise out of it?
      Please comment
      Thanks

    9. Hey Is there any way in which we can use a two ear headphones rather than a monophonic earphones

    10. ae matrix says: on July 11, 2011 at 10:36 am

      power slim for mp3

    11. Isthere any hearing aid to listen speech,words spoken in rooms or gathering muffling various frequncy noise?

    12. abhimanyu says: on November 9, 2011 at 8:01 am

      how to connect earphones …………cuz my earphones are not working

    13. can we use two ear head phones instead of mono ear head phones in the same circuit

    14. What are the major advancements on this hearing aid circuit

    15. whether this circuit is functioning or not

    16. Capacitors C1 and C2 seem to be large enough for a good low frequency response. However, I would connect VR1 to IC1 pin 7, to C2, and the VR1 runner to IC1 pin 7 (Just swap them). The reason for this, is when the runner of VR1 is turned down to minimum volume (nearest to the GND), the resistance that C2 will see, will be very low, and thus low frequencies will suffer. Our ears are less sensitive to low frequencies, and yet by turning the volume down, these frequencies are the first to diminish in the unmodified version of this design. C2 is large enough, when seeing a constant 10K of VR1, but NOT when it goes down when approaching GND. Oh, and get rid of LED1, it sucks! …. current! The TDA2822M is available as the DIL8 version, but also the SMD version of the same chip. WHY SHOULD THIS DESIGN BE DIGITAL, WHEN AN ANALOG DESIGN WORKS JUST FINE? On the whole, a very nice sweet and cheap design.

    17. hi al.i did this circuit.and theres no problems in soldering and circuit connections.after completion i could hear sound in my headset only wen i switch the pot on nd off.its jst coz of the mic present in the headset…i did change a new condenser mic bt it doesn’t work at all.plz tell me wat to do now..can i replace condenser mic with something else????

    18. Dave Kruschke says: on July 4, 2012 at 8:34 pm

      Where can one buy this ic in the US?

    19. Rowland says: on July 20, 2012 at 6:34 pm

      Pls if I add a sound detection circuit b/w the preamp stage n the IC input such that the amplifier will be ON only when an accoustic pressure is detected, will it work? Coz i want 2 use it for a project. For the detection circuit I want 2 use LM324 Op-amp and NE555, so i need your assistance : even a followup comment, thanks.

    20. hey! pls reply..
      i m working on this project and i m not getting the output… the capacitor before the mic shows 0.7V but deres no dc voltage on mic…pls temme the reason.
      also i cant get how to connect the potentiometer…
      plz help…its urgent…

    21. Jim Keith Jim Keith says: on October 29, 2012 at 1:31 am

      Are you sure you are using an electret capacitor microphone? like this one:

      digikey.com/product-detail/en/CMA-4544PF-W/102-1721-ND/1869981

      Link to specs are on this page.
      A dynamic mic will measure low DC voltage and have much lower output signal –especially if “paralyzed” by DC bias current.

      On the potentiometer, the center pin is the arm –if you get the other two swapped, it simply reversed the direction of rotation.

    22. sunday odo says: on March 9, 2013 at 3:46 pm

      I want a better explanation.

    23. ONGETA ONGETA says: on June 4, 2013 at 4:00 pm

      What if one uses TDA2822 instead of TDA2822M? Am having a problem with the two because I cant find out the difference between them.

    24. I soldered the components as they are shown in the circuit but but there is nothing coming out of at all. Pliz can someone help me on the possible errors that I may have made in the process.

    25. What are the expected results of this circuit diagram

    26. Check for reasonable voltage across microphone and transistor Vce (approx 1 to 2V). This may help isolate the problem. Hopefully, you have not installed the battery reverse because there is no reverse polarity protection.
      http://www.electroschematics.com/8817/battery-reverse-polarity-protection-in-lv-applications/

      Read my troubleshooting tips and take heed to my most important advice: “make no assumptions”
      http://www.electroschematics.com/8165/tips-on-troubleshooting/

      • Than you so much for the help you gave me yesterday. Am proud to say I made i. The sound is just clear. One of my classmates asked me , what is the gain of the gain of the amplifier that I used and the uses purpose of C3 , C 4 ,C5, C 7, C 8 and C 6 in the circuit. Pliz can you help me out.

    27. what are those capacitors with the value of 0.1 uF? is it mylar or ceramic?

    28. Hello, please, I would like to have an explanation about the value of resistor R2.
      Appears from calculations that I have done shows that the optimal value to avoid distortion should be about 90k. Could you kindly explain how you determined the value of 330k.
      thankyou in advance
      edoardo

      • Just guessing, but it must be to lower current drain to an acceptable limit without hurting distortion too much. Most transistor hearing aids (1980s) used a 220k base bias resistor with 1.5 volt Vcc. I agree with Dr. John Spunk and Jim Keith. A Stereo aid will help much with understanding speech.

    29. I am not getting the connection of the dotted line

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