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InterCom / Door Phone

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by Non89, Nov 11, 2010.

  1. Non89

    Non89 Member

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    now my casing and all finished, is time to prepare my presentation and report d.... any concept or main point for the circuit ? and how it function , transistor work for , why signal cabal connect from collector of transistor but not emiter or base?
     
  2. audioguru

    audioguru Well-Known Member Most Helpful Member

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    You learned how to simply solder parts together.
    If you need to know how the extremely simple circuit works then you must learn the basics of electronics.
     
  3. Non89

    Non89 Member

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    i not confirm the transistor part and does the circuit have frequency width?
     
  4. dave

    Dave New Member

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  5. audioguru

    audioguru Well-Known Member Most Helpful Member

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    What in English is a "frequency width"? Are you asking about the bandwidth of the circuit? You can calculate it.
    C1, C3 and C4 cut low frequencies and C5 cuts very high frequencies.
     
  6. Non89

    Non89 Member

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    how about C2, C6, C7?
     
  7. audioguru

    audioguru Well-Known Member Most Helpful Member

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    C7 and C7 filter the battery or power supply voltage so it doesn't bounce up and down with the audio. C6 stops the audio amplifier IC from oscillating at a high frequency.
    C2 filters the bias voltage fed to the transistor.
     
  8. Non89

    Non89 Member

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    how about the transistor ? why the audio signal transfer from collector and not the emiter ?
     
  9. DerStrom8

    DerStrom8 Super Moderator Most Helpful Member

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    Non89, do you even know how a transistor works? This question does not really make any sense.
     
  10. audioguru

    audioguru Well-Known Member Most Helpful Member

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    Each transistor has two outputs. One from the collector and another one from the emitter. The signals are out-of-phase and cancel (carefully adjusted with the trimpot) so your own voice does not come from your own speaker. Then there is no acoustical feedback howling and a voice-switch (half duplex) is not used.

    The signal from your transistor's collector goes to the other intercom station where it is amplified by its amplifier IC. The mic signal from the other intercom station's transistor comes to your amplifier IC.

    Both stations can talk and listen at the same time which is called "full duplex".
     
  11. Boncuk

    Boncuk New Member

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    Hi audioguru,

    are you sure you're not writing his "Dr. dissertation"? :D

    Boncuk
     
  12. Non89

    Non89 Member

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    “ The unusual feature of this design is the microphone amplifier Q1: its 180° phase-shifted audio output taken at the Collector and its in-phase output taken at the Emitter are mixed by the C3, C4, R7 and R8 network and R7 is trimmed until the two incoming signals almost cancel out. In this way, the loudspeaker will reproduce a very faint copy of the signals picked-up by the microphone. ”

    i m not understand on this part
     
  13. Boncuk

    Boncuk New Member

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    Hi Non89,

    R7 acts as a balance potentiometer in the circuit. If both signals from C3 respectively C4 have the same level at the center tap of the pot you won't hear any faint output of the own voice. If the 3/4 turn pot won't suffice use a multiturn (25 turns) pot to adjust for zero voice amplification of the own voice.

    Boncuk
     

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