Please anyone help me

Discussion in 'General Electronics Chat' started by spidermanIIII, Nov 22, 2013.

  1. spidermanIIII

    Thread Starter Member

    Nov 22, 2013
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    i have asked to do resonance type LC Meter by using transistors
    I searched in the internet and i found this schematic in this book in page 41 but there are somethings i couldn't under stand first what is fx that connected with spdt switch second when you look in pcb there are four terminals for FET transistor what is shield in the transistor finally what is the difference between variable capacitor and capacitor trimmer please anyone help me

    the book link here



     
  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    RCA phono jack or BNC. Do you know what periods are for?
     
  3. #12

    Expert

    Nov 30, 2010
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    A variable capacitor and a trimmer capacitor are the same thing, only the variable capacitor is usually larger.
     
  4. spidermanIIII

    Thread Starter Member

    Nov 22, 2013
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    i don't think these is RCA phono jack or BNC
     
  5. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    Well, the concentric circles denote a connector. I have no idea what connects to the FX input to your posted circuit.
     
  6. spidermanIIII

    Thread Starter Member

    Nov 22, 2013
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    this is full schematic of LC Meter
     
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  7. spidermanIIII

    Thread Starter Member

    Nov 22, 2013
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    the pcb design
     
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  8. MikeML

    AAC Fanatic!

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    After seeing the schematic, I'm guessing that Fx is where you would connect an external tuneable signal generator in lieu of using the internal oscillator. That should be discussed in the write-up that goes with the circuit.

    You can download the 12Meg book and read it as well as I...
     
  9. nigelwright7557

    Senior Member

    May 10, 2008
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    I think Fx is for an external clock.

    I did an LC meter using an oscillator and a PIC micro.
    You selected L or C then the PIC measured the frequency to determine the L or C value. It worked over USB on a PC and worked very well.
     
  10. vk6zgo

    Active Member

    Jul 21, 2012
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    T1 is a crystal oscillator which feeds T2 via S3.
    In its alternate position,S3 allows you to input a signal from an external Signal Generator,if you wish to.


    T2 (FET) is,as the schematic implies,a buffer stage,to reduce the effect of changing load impedances upon the xtal oscillator..
    The “shield” connection is just that –an electrostaic shield used in some transistor packages.


    The next stage,T3,is an emitter follower,& as noted on the page,is a power amplifier.
    Emitter followers have power gain,but not voltage gain..


    This drives the LC network.


    Dip metering.
    When the series LC network consisting of Lx & Lw both in series with the parallel combination of Cf & Ct is at resonance,the network appears as a low impedance in parallel with R8,thus reducing the RF voltage available at that point,& available to detector circuit D3.D4,resulting in a “Dip” on M2.


    Peak metering
    With S4 off & S5 on, the detector circuit D1,D2 is connected across the capacitive leg of the resonant circuit.
    At resonance,the voltage acroff Cf,Ct in parallel is at its maximum,so this results in a “Peak” on M1.
     
  11. spidermanIIII

    Thread Starter Member

    Nov 22, 2013
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    Thank you for your answer . Now I understood
     
  12. spidermanIIII

    Thread Starter Member

    Nov 22, 2013
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    can anyone help me in doing the packaging for variable resistance and variable capacitor and spdt switch in Proteus to do this circuit in PCB
     
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