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Hi everyone! Can i ask why is there a diode here?

Discussion in 'General Electronics Discussion' started by Elecsman, Nov 27, 2015.

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  1. Elecsman

    Elecsman

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    Nov 27, 2015
    Hi everyone! Can i ask why is there a diode here? is it essential? what does it really do to the circuit? I'm trying to understand the circuit better for my presentaition. Thanks for you answers :)))
     

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  2. duke37

    duke37

    5,277
    733
    Jan 9, 2011
    Q3 seems to have gone missing.
    Q2 and Q4 form a multivibrator oscillator with the buzzer setting the frequency.
    The whole of the buzzer current goes through the base of Q2. This seems to be wrong.
    I do not know the purpose of the diode, perhaps it has something to do with the missing Q3.
     
  3. Alec_t

    Alec_t

    2,736
    724
    Jul 7, 2015
    The circuit operation would seem critically dependent on the buzzer type/properties, which are not given. The diode may be there to block a back-emf spike generated by the buzzer ...... who knows?
    The R1-R3 values are surprisingly low.
    Where did you get this circuit?
     
  4. Elecsman

    Elecsman

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    0
    Nov 27, 2015
    http://www.instructables.com/id/Laser-Tripwire-1/
     
  5. Tha fios agaibh

    Tha fios agaibh

    2,078
    687
    Aug 11, 2014
    People commenting on that site, can't seem to get it to work.
    Good call duke37.
     
  6. davenn

    davenn Moderator

    13,437
    1,807
    Sep 5, 2009
    yup
    The instructables site is famous for useless and crappy circuits

    @Elecsman .... if I were you, I would seriously forget about anything from that site ... its just not reliable


    cheers
    Dave
     
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