Please anyone help me

Thread Starter

spidermanIIII

Joined Nov 22, 2013
78
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



http://www.mediafire.com/download/sopvv90ode72w7j/electronics-for-you-projects-and-ideas-2000.pdf
 

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#12

Joined Nov 30, 2010
18,217
A variable capacitor and a trimmer capacitor are the same thing, only the variable capacitor is usually larger.
 

Thread Starter

spidermanIIII

Joined Nov 22, 2013
78
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
this is full schematic of LC Meter
 

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Thread Starter

spidermanIIII

Joined Nov 22, 2013
78
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
the pcb design
 

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MikeML

Joined Oct 2, 2009
5,444
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...
 
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.
 

vk6zgo

Joined Jul 21, 2012
677
this is full schematic of LC Meter
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.
 

Thread Starter

spidermanIIII

Joined Nov 22, 2013
78
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.
Thank you for your answer . Now I understood
 

Thread Starter

spidermanIIII

Joined Nov 22, 2013
78
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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