Listening Bug

26 February 2016 User Review

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This DIY electronics hobby kit can be used to listen what is going on in another nearby room. This is very useful for parents to monitor their children’s activity through sound. This is an interesting and inexpensive spy electronics project. As a spy gadget, this DIY project can be demonstrated as a mini project by students and all electronics hobbyist.

Working of Listening Bug:

Listening Bug as a DIY project is a simple and hi-fi device which uses many electronic components like resistors, capacitors, a microphonetransistors, an opamp and a speaker. With the help of condenser microphone in the circuit sound waves from about 6 meters can be converted into electrical signal. IC 741 is used in inverting mode to amplify the signal produced by microphone. Output from this IC is again amplified with the help of push-pull amplifier using transistors AC 187 and AC 188 pair. This amplified signal is converted again into sound with the help of a loud speaker. Gain of operational amplifier can be changed by varying the feedback using 2.2 M pot in this DIY project.

For obtaining increased sensitivity, the condenser microphone in the DIY project must be enclosed in a better enclosure. Soldering and mounting processes must be done with care and necessary precautions should be carried out to avoid PCB damages. Listening Bug Kit is an easy and comfortable kit for the users.


Electronic Components:


  • R1 : 3.3K
  • R2 : 4.7K
  • R3,R4 : 10K
  • P1 : 2.2M


  • C1 : 47KPF
  • C2 : 10UF/25V
  • C3 : 220UF/16V
  • C4 : 100UF/10V


  • Q1 : AC 187
  • Q2 : AC 188
  • IC  : 741


  • MIC : COD. MIC
  • SPK :  8 ohms/0.5W
  • PCB

Applications of Listening Bug:

  • Good as a spy gadget.
  • Listening Bug can be useful for mobility impaired and paralyzed patients.
  • This DIY project can be used as a toy for children.

Listening Bug is a DIY project useful as a spy gadget and also to common people. This will be an attractive one as a project.

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