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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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    oic , i tot i only need to use 1 output .... ok , i will try it...

    the polarity of both C4 capacitors having problem ?
     
    Last edited: Mar 4, 2011
  2. audioguru

    audioguru Well-Known Member Most Helpful Member

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    The original circuit and Boncuk's circuit have the polarity of both C4 capacitors backwards.
    The emitter and collector of the transistor have positive voltages and the resistors to ground at the other ends of the capacitors is 0VDC.
     
  3. Non89

    Non89 Member

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    ok , i will exchange the polarity of C4
     
  4. dave

    Dave New Member

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  5. Boncuk

    Boncuk New Member

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    Did you consider the 180degree phase shift between C3 and C4?
     
    Last edited: Mar 4, 2011
  6. audioguru

    audioguru Well-Known Member Most Helpful Member

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    Of course there is a 180 degrees phase shift in the signals. But it is AC and has no polarity.
    The polarity of C4 is backwards to the DC.
    I fixed my copy of the original schematic:
     

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  7. Non89

    Non89 Member

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    may i ask where can i find the BEL187 npn Transistor datasheet ( where is emitter, base and collector) , and what transistor can replace it ?
     
  8. audioguru

    audioguru Well-Known Member Most Helpful Member

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    Why are you asking about that very old transistor in this thread? The transistor was made in India by Bharat Electronics Ltd a few centuries ago. I can't dind a datasheet but I found its spec's on a list of old transistors.
    Today I would use a 2N4401, 2N222A or BC337 and see its pins on its datasheet.
     
  9. Non89

    Non89 Member

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  10. audioguru

    audioguru Well-Known Member Most Helpful Member

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    If you make the original circuit correctly then it will work perfectly. But you made only half of it so of course it didn't work.

    The new circuit is simply a very old audio amplifier. It is bad because it has DC in the speaker and the transistors are biased wrong. A simple IC amplifier can replace it.
    Two circuits make an intercom that will howl all the time because the sounds will go around and around.

    The original circuit avoids howling feedback because it cancels your signal from your speaker.

    When you said "discordance" do you mean that this intercom produced acousical feedback howling like I explained?
     
  11. 4pyros

    4pyros Well-Known Member Most Helpful Member

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    opps! Sorry I could not resist.
     
  12. DerStrom8

    DerStrom8 Super Moderator Most Helpful Member

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    Hahaha! There's more where THAT came from! :D :D
     
    Last edited: Mar 7, 2011
  13. Non89

    Non89 Member

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  14. DerStrom8

    DerStrom8 Super Moderator Most Helpful Member

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  15. 4pyros

    4pyros Well-Known Member Most Helpful Member

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    What AC are you going to hook it up to?
     
  16. Non89

    Non89 Member

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    LOL...you are so evil... of course i nothing going to try it =.=
     
  17. Non89

    Non89 Member

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    i was connected up both circuits by just using jumper wire and supply voltage on both circuits respecitvely......

    the diagram show the voltage i meansure E,B,C,SPA,SPA respectively with Ground......

    the output voltage from pin2 of potentiometer was extreamly low.... it just 0.0x - 0.5... i change both C3 & C4 polarity, but the result of pin2 output voltage is almost same... any idea ??
     

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  18. Boncuk

    Boncuk New Member

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    Hi Non89,

    wrong again!

    C3 connects to the collector of Q1 with it's positive terminal and C4 connects to the emitter of Q1 with it's positive terminal.

    So only the polarity of C4 has to be corrected. (both boards)

    I contacted the author of the circuit and he will remedy his design soon.

    When googling for the design use the search words "full dulex intercom". You should find this page:

    Full-duplex Intercom - RED - Page78

    Boncuk
     
  19. Non89

    Non89 Member

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    thank Boncuk~

    by connecting both circuits with jumper wire and supply on both circuits respecitively.... the sound can transfer from "master mike" to "master speaker" , " slave mike" to slave speaker" ..... but the sound is very small..... how to amplify it ??
     
  20. Non89

    Non89 Member

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    yaya, i know .... i just trying both for testing XD
     
  21. Non89

    Non89 Member

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    this is what i tested with changing C3 and C4 .... both connected +12V DC supply respectively....

    C3 and C4 positive polarity connected to Q1 , jumper wire was connected between both circuits Q1 Collector : Speak in mike 1 or mike 2 = Both Speaker voiced out

    C3 positive polarity connected to Q1 , C4 negative polarity connected to Q1, jumper wire was connected between both circuits Q1 Collector : Speak in mike 1 or mike 2 = Both Speaker Voiced Out

    C3 and C4 negative polarity connected to Q1 , jumper wire was connected between both circuits Q1 Collector : Speak in mike 1 or mike 2 = Both Speaker voiced out

    (all the voiced out from Speaker 2 was not clearly....)



    now i pull out the jumper wire and changing the C3 and C4 as 3 solution above, and you can guess the result as shown : Speak in mike 1 = Speaker 1 voiced out, Speak in mike 2 = speaker 2 voiced out(but very quietly....maybe i will change the R10 and R11 value or instead with potentiometer)
     
    Last edited: Mar 8, 2011

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