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    With this sound activated switch, control by sound may be very useful, not just on a robot but also for a bit of home automation, for example a sound-activated light responding to a knock on the door or a hand clap. The light will be automatically switched off after a few seconds. An alternative use is burglar protection — if someone wants to open the door or break something the light will come on, suggesting that someone’s at home.

    The circuit can work from any 5–12 VDC regulated power supply provided a relay with the suitable coil voltage is used.

    Schematic of the sound activated switch circuit

    When you first connect the supply voltage to the sound activated switch circuit, the relay will be energised because of the effect of capacitor C2. Allow a few seconds for the relay to be switched off. You can increase or decrease the ‘on’ period by changing the value of C2. A higher value results in a longer ‘on’ period, and vice versa. Do not use a value greater than 47 μ F.

    Biasing resistor R1 determines to a large extent the microphone sensitivity. An electret microphone usually has one internal FET inside which requires a bias voltage to operate. The optimum bias level for response to sound has to be found by trial and error. All relevant electrical safety precautions should be observed when connecting mains powered loads to the relay contacts.

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    102 Responses to "Sound Activated Switch Circuit"

    1. hey man,

      we are doing a project for a circuits class and i was wondering if you had further information on this circuit because it seems really interesting. do you have any specifics of the mic or the other components. thanks,


      • Hello,Mr.logan.I can tell you all detailes about that circuit;
        [“Sound Activated Switch circuit”]and analize it.



    2. I just have a few questions about what kind of michrophone and info on the relay.

    3. maybe you can help me . how can i .. used this circuit in my pc i want the pc sound output to trigger the relay ..thanks

      • You can disconnect the microphone and connect the audio cable directly between PC and this sound activated switch. Then adjust the volume of the sound until the relay is triggered.

    4. dhaesa pramana says: on July 13, 2009 at 2:12 am

      i just wanna ask
      1. how to change the circuit to make the circuit can “ON” when the first sound then “off” when the second sound

    5. Hi, I have built this circuit, but it doesn’t work! Only change i made was instead use electrolytic C1, I used tantalum, which I don’t think it will make any different, I don’t know what is wrong with it, can someone please help me! Thanks…

    6. thank you so much for the information! it helps me a lot!

    7. i just wanna ask
      how to change the circuit to make the circuit can “ON” when the first sound then “off” when the second sound

      • Hello,Mr.Oppong Akwasi,

        I can make the circuit that you asked for
        and also some nice projects,too.
        Here are my mail;[bah9mh@yahoo.com].


    8. the project is really interesting. we would lie to know more about the project. details. specifications…

    9. Have you experimented with specific sound recognition, something like a whistle or bell that will cut through other noise and give a clean signal. Most of the “clap lights”I have experienced lack definition.


    10. good cirkit have you experimented with specific sound recogniting ;something like awhistle

    11. We would like to know more about this project sound activated switch.So please send us more information along with the circuit diagram.We have planned to do a project on it.

    12. a i would like to know what is RE1 i new in this field

      • BHARAT CHANDRA says: on September 22, 2015 at 4:36 pm

        RE1 is a electromagnetic relay.
        the signal from MIC1 will be amplified and sent to the relay, which will trigger the next circuit.

    13. can u help me too by elaborating on relay n microphone , as before fabricating to pcb i will try it out on a software “capture cis” and then i will fabricate so quickly help me

    14. do this circuit works on the principle of bistable multivibrator

    15. how to change the circuit to make the circuit can “ON” when the first sound then “off” when the second sound

      • Adnan Rafiq says: on November 30, 2011 at 11:58 am

        i am also need this circuit.if you have please share it with me.you can contact me.i am a electrical engineer.my phone number is +923327929262.

      • Hello,Mr.asif ali,

        I can make the circuit that you asked for
        and also some nice projects,too.
        Here are my mail;[bah9mh@yahoo.com].


    16. can any1 tell me what sort of mic should i use??

    17. we can use mic from regular microphone, or you can use from mic of cellphone.

    18. onome sheriff says: on April 3, 2011 at 6:41 pm

      how can we prevent other sound from activating the switch

    19. what kind of capacitors i need to use? please show me the pictures of this capacitors

      i have not 4.7 mF no-polarity capacitors!!! i need use 475 capacitor?

      i think 104 = 1n0 ? is this capacitors used in scheme?

      please tell me mans

    20. I made scheme but i have trouble

      on RE1 contacts with no sounds i have 0.05 V
      with very big sounds around i have 0.10 V
      and i can view increase volts with increase sound around

      my microphone from mobilephone and have 1.2 kOhm

      sorry. with no sounds i have 0.15 V
      when i increase sounds i have 0.18 V

      with connected parallel resistor 57 ohm i not see reaction or increasing Volts

      it is my scheme with volts

      i need replace R1 to small Ohms? 4k7, 3k3, 1k8 ? to increase sensity

    21. all works

      just microphone very sensitive

    22. Hey kolio since you have completed the circuit could you give me the list of items required for this diagram to work? Thanks alot!

      From: Chester

    23. IT’s working. perfect! I made this 1hours ago. I have using the T1(T2) – BC547 instead of 2SC945 part. It has no problem. Thax.

      • Detllef says: on August 8, 2011 at 1:12 am

        Hi, can you send me the scheme and a part list. Im here in the Dominican Republic and I have to order it in the Staates. So it should be right. Thanks a lot.

      • You’ve got a mail-!. Please check ur eMail box.

      • nhel romano says: on October 15, 2011 at 1:39 am

        could you pls. send me the scheme and the parts list, i quite couldn’t understand the diagram. I’m hoping for your positive response regarding this matter. thanks.

      • To nhel romano.

        OK. I will do it but…

        Please, let me know that your homepage, weblog or email if you like to receive it.
        The posting on this comment area not allowed a long part list.
        So, you should have a email at least.


      • hi..could you please mail me the scheme & parts list pls…
        my mail id is “lightray.rekha@gmail.com”
        waiting for your responce..
        thanx.. rekha

      • HI..
        could you please mail me the scheme & parts list pls…
        my mail id is “pirate_king113918@yahoo.com”
        waiting for your responce..
        thanx.. AZ

      • could you please mail me the scheme & parts list pls…..my mail id is “nsm_bahary@yahoo.com”

      • maheshjshetty says: on August 22, 2013 at 2:53 pm

        yong please send me the right circuit diagram and my email:jaysunrasmah@gmail.com.

      • could you please send me the scheme and the parts list, i quite couldn’t understand the diagram. Im hoping for your positive responce regarding this metter.

    24. i made this circuit. but its not working..!!
      the relay operates as soon as the supply is switched ON. The transistor t1 is not saturated. can anyone tell what could be the problem?

      • Adnan Rafiq says: on November 30, 2011 at 11:55 am

        Please contact me i will give you information.i have also need infomation.my phone number is +923327929262.i am a electrical engineer

    25. I made the circuit. but its not working!
      the relay operates as soon as i connect the supply. the supply is of 12 volts & relay too.
      the transistor t1 is not saturated.
      please tell what could be the problem.

    26. Hi
      i am making this project but the circuit is not working the changes made i used for C1=47uF electrolytic and for C2 the same value until now i did not get solution
      can you help me i need detailed explanation
      about capacitors

      • It’s working with C1=C2=47uF.
        I have tested it with breadboard.
        In your case, It very high sensitive, so it work by even breath sound.
        I do not recommend it out of range capacitors.

      • Hello,

        You can replace certain components to reduce the sensitivity of the circuit.

    27. Hello,
      can u please let me know with the present design,what is the time it take for the circuit to go “OFF” after a sound activated “ON”

    28. I will introduce how to choose good MIC.
      Good choosing a MIC: for making “SOUND ACTIVATED SWITCH CIRCUIT”.
      Good Condition:
      – category: Microphones
      – Type: Electret Condenser
      – Size / Dimension: Circular – 10mm Dia x 5mm H
      – Sensitivity: -38dB ±2dB
      – Voltage Rated: 4.5V
      – Impedance: 2.2K Ohm
      – Frequency: 38Hz ~ 16kHz

    29. Announce to making failed outsider.
      I had not designed this circuit. I am person who making succeed just.

      I will let you know making tip:
      – You should not supply over the total DC 6volt.(because : the MIC is DC 4.5 volt).
      – The 0uf condenser: You should use the Tantal 0uf1(=0.1uF=100nf) type. This has positive and negative Polarity. Do never use ceramic, film or electric types. It relative the frequency.
      – The 4u7 condenser: You can use electric type 4.7uF only. It is general.
      – I have using the T1(T2) – BC547 instead of 2SC945 part. Sure, you can use 2SC945 too.
      – The resistor: do not over 5 % but I recommend 1 % resistor.
      – In addition: you need 3M tape for a adjusting the MIC’s sensitive.

      Good Luck.
      From: Yong.

    30. Additional comment:
      If you follow my guide line, then you never supply over 6 volt. It under condition the MIC’s Max voltage.
      I recommend the 5 volt regulator. (example: IC-7805 regulator)

    31. this circuit was big help, I used it as a project on my subject in control system. It really works. Aside from an encountered problem during lay outing.. but as soon as i finished i was amazed. :)

      • hi..could you please mail me the scheme & parts list pls…
        my mail id is “lightray.rekha@gmail.com”
        waiting for your responce..
        thanx.. rekha

    32. what electrical components do u need to make a voice activatedswitch

    33. Guys, im really interested in building this miracle.
      If it is not hard for you, would u mind sending me the list of items required for building.

    34. Guys, i am really interested in building this miracle.
      If it is not hard for you, would u mind sending me the list of items required for building.

    35. sorry for double posting.

    36. sir , can i use bc547 (general purpose transistors instead of 2sc945 or c945 and will i use bc327 or bc557 instead of bd140
      send me information later

    37. sir i want to make a better major project for the sixth sem and i like this project very much give me the other better sugesstion

    38. I want to connect a 5 point eagleman relay to circuit can u give me the pin description

    39. Hello,everybody and ;Mr.asif ali,Mr. Adnan Rafiq,Mr.dhaesa pramana,Mr.Oppong Akwasi.

      I can make the circuit that you asked for
      and also some nice projects,too.
      Here are my mail;[bah9mh@yahoo.com].


    40. Sir, i want the circuit to ”on” on 1st clap, n ”off” on the n3xt. Pls help me .
      I want the detailed list of components.

      • Hello,Mr.rohit,
        Here I attached that circuit you asked
        for it.I tested it with Proteus and work
        correctly.So,please try it and let me know if it works correctly?

        Best Wishes,

    41. Hello,Mr.rohit,
      I will design that circuit for you and
      test it by PROTEUS too for sure.
      And also I will send it to you,soonly.
      But,if that circuit have an extra detailes,please send all detailes to
      my mail;[bah9mh@yahoo.com].

    42. This circuit is ♌φτ̲̅ coming on, do I have to increase or reduce the Mic biasing resistor? What should I do to make this circuit work. Every component have been connected in their right polarity according to the circuit diagram.

    43. nice project.

    44. mr logan i want switches which wear working on the voice control,for example in i robet movie…….
      reply me plz ………
      i searching for this type of project

    45. This circuit it doesn’t work, i am try 3 time but
      …actually i wasted my time…

      • James Wang says: on July 6, 2014 at 1:14 pm

        get your lesson in electronics,perhaps you can go to school like MIT(Massachusetts Institute of Technology) thank you!

    46. Charles Logan says: on July 25, 2013 at 7:46 am

      Will someone please mail me the circuit diagram of project similar to the Sound activated Switch.. Only Difference is I Want the Switch to turn ON on 1st Sound and Turn OFF “ONLY when 2nd Sound is made” i.e the switch should remain ON unless sound is made to turn it off… plzzz mail me circuit diagram, components with specifications n please test it on “PROTEUS” or any other Simulation software n tell me the name of the software ..i want it for a mini project.. my email ID is clawssn@gmail.com

      • Bahman Mohammadhoseini says: on August 9, 2013 at 8:14 pm

        Hello.Yes I have a design bymyself[a practical circuit]of sound[clap]activated
        switch to be turned ON for the first clap and turned
        OFF for the second one.You can send your request to
        my mail;[bah9mh@yahoo.com];I realized it and it works
        correctly also I tested in with PROTEUS.

        Have a nice day,

    47. ‘Bahman Mohammadhoseini’>>>>sir i want that practical circuit of sound[clap]activated,and i built tht above circuit in proteus but i dnt get tht microphone there,

    48. Bahman Mohammadhoseini says: on October 3, 2013 at 8:50 pm

      Dear Mr.Omkar,
      Hello.Please send your e-mail to my mail;[bah9mh@yahoo.com]so I can send you my clap switch design.
      Also,in older PROTEUS version there is not exist a
      microphone component and also you should give it an
      audio wave like a clapping sound as an input so you can simulate that circuit;and user should be a professional to work with it correctly.

      Have a nice day,

    49. HI..
      could you please mail me the scheme & parts list please …
      my mail ID is “dxcircuits@zoho.com”
      waiting for your response..
      thanks.. Sandpit

    50. Could u plz send me the real list of this curcit

    51. if there are too many switches in a room the how can we access the different switch as per our requirements

      • Bahman M. says: on July 6, 2014 at 5:42 pm

        Hello.You should use coder to assign a special addresses[names]
        to each individuals switches to call or activate each of them
        we you want.

    52. can i ask how specific that C2 and C1,how many volts?electrolytic or SMD,tantalum??..thank you

      • Bahman M. says: on July 6, 2014 at 5:35 pm


        Those C1 & C2 because of their values and ranges are
        polarized type,so,they can be electrolytic or tantalum types.
        Also, you should be noted that in sound wave,for our ears there is not difference between a negative half cycle or positive one.

    53. 1.what sound should i give to mic so to get required proper output….?
      2.for relay what is exactly used either a coil or a no/nc connection ??

      please give the reply as soon as possible.

      • Mr.Manish,

        The answer to your questions are;

        1.Just sound of clapping[the sound of striking your palms together].

        2.Use coil pins of relay,a transistor and a diode.

        [I also, designed a very practical sound switch with a relay that work very good.].

        Have a nice day,

    54. I am creating a suit for my shows and I am using around 22 feet of EL wire running off a 9V battery and an inverter. Could I use this circuit to control the input of the inverter? Meaning, can I put the battery into this circuit, and run the circuit output into the inverter?

      And also, will changing the value of capacitor 1 change anything?

    55. And another question I have is would it be safe to use a potentiometer for resistor one?

    56. Hello, I have a driveway alarm, it beeps twice whenever a car or being passes through it. It consists of the sensor outside and the alarm signal box located indoors. I need a sound activated relay to activate when this alarm goes off. Then a relay would power a security light directed to the driveway area. I have searched the Net but haven’t found anything that would work. Any Ideas ? Thank You in advance

    57. I’m just wondering, how much sound would it cost for this circuit to activate.. Coz i need a minimum of 70dB as the input sound.. can you help me at this? thanks a lot bro :))

    58. I’ve made a clap switch circuit using a relay. But it is too sensitive, for ex a click of ball point is enough to glow a light.
      how can i make it less sensitive. i want it to operate only on a sound of clap…..

    59. Ughhm… I have this project. We have to make a toy car which is clap-activated. Can u guys help me?

    60. otskaurgmail-com says: on April 18, 2016 at 2:50 pm


      Can anybody tell me what 060379 – 11 stands for? I can’t seem to find any information about this part.

      Thank you

    61. moch-rizal25gmail-com says: on April 30, 2016 at 3:14 am

      Dear Bahman,

      Can you please send me the simulation project, the scheme, part list, or pcb layout?

      When i try it in breadboard, it is failed. I dont know why, im still new in electrical. So please can you help me? Or anyone that has already succeed with this circuit.

      Im already send you an email. It is moch.rizal25@gmail.com

      Thank You

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