Most used Circuits

Most used Circuits by Project Builders






Mobile Bug Modified Circuit


 This  Circuit is more sensitive and gives around 2 Meters range. Show active Mobile phone 2 Meters above the circuit to get maximum range. Antenna is not needed if the circuit is exposed. If it is enclosed, use 30 cm plastic wire as antenna or use a Telescopic areal like that of Pocket radio. Always keeps 0.22 cap in vertical position like a loop antenna.Use only large disc 0.22 capacitor. Its lead length should be 18-20 mm.


  1. Mobile Bug – Circuit Design
  2. Mobile Bug – Trouble shooting
  3. Mobile Bug- Power Point Presentation
  4. Mobile Bug- Full Project Report
  5. Mobile Bug – Original Circuit
  6. Mobile Phone Working Theory
  7. Mobile Phone Radiation

Mobile Bug Images

Mobile Bug Circuit on Common PCB


Mobile Bug Assembled


Mobile Bug PCB1


Mobile Bug PCB2



Mobile Bug Video

ErnaTamizi  from Malaysia successfully completed the Final year project. See how the Mobile bug is working. Well done Erna.



Noise Meter







Pyroelectric Fire Alarm









Mobile Sniffer Viva Questions
  1. Mobile SnifferSkin Response Meter Viva Questions – Skin Response Meter- Viva Questions

43 thoughts on “Most used Circuits

  1. Sir that .022 uf disc capacitor is unavailable in our chandni market(west Bengal).can u plz suggest any alternatives and i am using the modified if u can tell me any thing about how to increase the detection area and show the output in other way like using 7 segment display, that will be helpful to me.I am working on this project in my final yr project.

  2. hai sir;
    i have a doubt on mob sniffer
    what is unit 2 near to c6?is it unit 1 itself?is two units necessory for proper functioning

  3. Sir,
    I have tried the project Mobile sniffer in common board. But it did not work. There is no signal variation at the output of diode with and without mobile phone. Can you suggest any trouble shooting procedure as in the case of mobile bug. Also is there any noticeable point regarding the spacing of diode lead length etc?

  4. hey sir,can you please tell me how to increase the range of this that it can be used more effectively

  5. hello sir,
    i want to make a circuit which increases mobile signals strength because my home is surrounded by many apartments which reduces the signal strength
    can you please provide details about the circuit and components required to make the circuit

  6. hello sir i have done mobile bug circuit in spring board and it is giving me 3.5 meter radius rage but the problem is sometimes the buzzer starts if non of the mobile is activated also, and it keep on buzzing only and it never stops after turning off the power supply and turning on again it will stops buzzing plz help me sir what is my problem. i am shortly doing this in pcb. i have a ready made pcb i got it in some electronic shop.

    thank u

  7. Hello sir i do noise meter project after i finish my connection the LED IS continuously glowing which is connected at 10 pin of lm3914

  8. Hi,
    Diodes as voltage suppression provide a simple solution to increase the EMI and ESD immunity level of a circuit and only a few guidelines must be followed to
    provide effective surge protection.
    Thanks for this informative post.

  9. Hello Sir Good Day
    Sir I’m doing Mobile Sniffer Project as my BE mini project in my college. I’m not finding 1N3491 Diode anywhere in INDIA which forms a Major element.
    Please Sir could you tell me where can i find this diode any source, where this diode is used in any electronic instruments Or please tell me any equivalent diode for this.

  10. hi sir,
    em Avinash ,
    i am doing the mobile detector project as my BE project
    your work & information about this project guided me in many ways.
    i thank u for sharing ur valuable information through online sir.
    my doubts are:
    1) I build the circuit i am getting output for range of 1.5 meters if i use dipole antenna or multi stage op amp the range this circuit increases?
    2)is gigaherts signal detector circuit( and mobile detector circuit ( are same? (ie is they provide same range?)
    3)i got another circuit that works for 8 meters( in this circuit i am not finding diode 1N3491 in india(online &offline) which is important component in that circuit
    i am trying several equivalent diodes but it is not working can u give me suggestion to this problem sir
    tenx for ur time sir

  11. D.Mohankumar
    could you please help me in this project
    How can I expand the range of detection ?
    please answer me as soon as possible.

  12. D.Mohankumar
    Could you please help me in this project
    How can I expand the range of the detection . It is important for me if you please answer my question as soon as possible

    1. It is better to construct in Common PCB since loose connections in bread board may affect the response of the circuit.You can use a plastic wire as antenna.

      1. sir i am building the mobile bug but i confused with the 8mm lead spacing specification. What does it mean – the distance b/w soldering points should be 8mm OR the distance b/w the two leads at the point where they emerge from capacitor should be 8mm (means i have to buy a cap with 8mm lead spacing specification) ? pls reply i have to submit my project next week.

      2. 8 mm spacing means approximately between the solder points connecting the cap. 18 MM height means, the length of the leads projecting from PCB. THe 0.22 disc cap has 24 mm length.
        see this link

  13. Resoected Sir,
    I am making solar portable laptop charger but facing problem to get the laptop battery charged while working on computer in parallel. Beside while computer is shutdown the battery draws only
    0.3 to 0.5 amps only . I have used simple regulator even then same problem. while an ordinators battery draws quite good current to get it charged say 1.5 to 2 amps. SPV modules are of 50watt and volts on load 17.5v volts on no load 19.2v.
    Also the charging light remain flickering when connected to solar panels may be variation in light intensity.

    Computers battery rating is 10.8v, 4.4amps.

    When my laptop is being charged through elect. adopter it draws 1.2 amps to get the battery charged during shutdown position and 2.5amps while working on computer.

    Plese suggest how a constant voltage can be got from Solar system specially for laptop.I put auxilary nbattery in parallel to laptop battery even then same problem and beside charging the laptop it stopped and keep charging only the auxilary battery ( rating 12.8v , 2.8ahrs)

    I will be highly obliged if can be helped to suggest some circuit for regulator to solve this problem.


    Sharma RS

    1. Dear Sharma,

      Solar panels can deviver milli ampere current ranging from 100 mA to 500 mA depending on the size. Soar panel is used for continuous charging with low current to avoid over charging. The voltage and current from the solar panel depends on the duration and intensity of sunlight.It is better to keep a standby battery connected to solar panel. Use it after 24 hours of charging.Quick charging is not possible with solar panel.

  14. hello sir
    i have been trying mobile sniffer,but i am unable to know more about the compact 12v battery.please give me some idea about that one since i want to make compact mobile sniffer

      1. sir
        could u please give some company details of the 12v car remote battery or some image reference,so that icould easily get that one

  15. Hello Sir,
    you didn’t replyed me about how to connect JFET between the IC1 and capacitor. But you told about changing the value of resistor which will do. But I need information about the JFET and its operations.

  16. hello sir,i have done solder completely but the problem is if i connect the the battery immediately buzzer starts sounding …how to correct this ?

  17. hello sir, actually im using a paging technic instead of sounding a alarm. paging means it will display the message in can i achieve this after getting the output of ic1 ca3130….if u have any idead plz tell me…

  18. ….good day sir?
    i have a problem is it possible that the range of the of mobile bug detector increase up to 10 meters or more in radial…if possible what circuit i’m going to use….
    ….i want to know it soon…
    thank you..

    1. Hello
      It can give 2-4 meters radius if properly oriented. Only way is changing the feedback resistance of IC1.470K and IM resistor in series can improve the range. Also try with 100 Kto 4.7 M ( 100K,150K,470K,560K,689K,1M,1.5M,2.2M,4.7M) only through trial and error you can achieve the result. If you increase the range, possibility of false triggering increases due to increase in sensitivity. That is, the RF signals in the standby mode can trigger the circuit. Try and inform the result.

      1. D.Mohankumar
        could you please help me in this project
        How can I expand the range of detection ?
        please answer me as soon as possible.

  19. sir i tried ur skin response project,but the problem is with presets…can u just give a brief idea on how to adjust the presets as everytime i tend to get different outputs even after setting the presets……… waitng for ur reply

    1. Hello Justin
      After assembling and powering the circuit, carefully set the presents.Remember, the skin resistance never remains steady for long time, it always vary depending on the physiological conditions.Also this may vary in different persons. The best way to set the present is…. select a person ( Calm one is good and setting in the morning is nice) with high skin resistance and after attaching the touch pads carefully adjust the wiper of preset using a small preset screwdriver. During adjustments, do not touch the body of the person or the circuit or on the preset and metal part of the screwdriver since this may change the conductivity. If the setting is satisfactory, glue the preset using wax so that, the setting will not change due to shaking.

  20. sir, i connected the circuit (mobile bug) exactly as shown…the LED lights but the problem is with the buzzer…the buzzer keeps ringing when i supply the source voltage….i tried connecting the circuit atleast 3 times because of the buzzer but in vain…… to be more specific about the ringing of the buzzer…..if i insert the buzzer wire in pin 3 nothing happens (no sound) but if i take the wire out and touch it to the metallic pin 3( of ic 555) which is the portion of the ic visible above the breadboard,,then the buzzer starts buzzing….AND NOW if i insert the wire in pin 3 then it continously keeps buzzing…thats the thing that i noticed(only if i bring the wire in contact with the metallic portion n then insert it in pin 3 it keeps buzzing)..but it does not stop…..i think the buzzing tells us that there is current passing through output when voltage is supplied..i really dont know what is my mistake..what do you think is the problem…..kindly try n reply…thanking you in anticipation..


Add your Comments here and Click Post Comment. For Queries, come to the Discuss and Share Forum

Please log in using one of these methods to post your comment: Logo

You are commenting using your account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s