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Capacitance meter making -

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thannara123

thannara123

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I want to make a capacitance meter .
firstly i need to make a frequency generator (whose frequency is varying in accordance with the capacitor which have to measure )

Which frequency generator can i use . If i use 555 is it enough
In my calculation ,to measure a .002 micro fard capacitor the output frequency is 72 Mhz ,

I want to use micro controller to count the frequency to display the capacitance ,
But i have the controller as follows Pic 16f877a , 8052, atmega 8
the operating frequency of these controler is less .

Then how to i use / select please help me.
 

You will never get 72MHz from a 555 timer!

If you look at the many designs for capacitance meters you will see they work on a different principle. They time how long a charge is held on the capacitor by using switches and a comparator.

You can do it by measuring frequency but to be practical to build you need to keep the frequency fairly low (< 50MHz) and you need to use a circuit in which the capacitor is the primary frequency deciding component. This usually means an RC or LC network where L or R are small compared to the capacitor value.

Brian.
 

What are the other best principles for do it ?

- - - Updated - - -

By apply a known voltage at a known frequency, measure the current and do a quite
complicated calculation to get the answer.

can i get more reference or tutorials
 

hello,


you only need to use a better version of NE555 like ICM 7555
with a big resistor value as 2,2Mohms, so you can achive a resolution better than 0,1pF
and add autocalibration for Zero and full scale.
with Q=20MHz
Used as an accurate monostable, it measure the time (teta=R*C )to load the capacitor until threshold value is reached.
see application on my web page... and comparaison between classic 555.
Autocalibration compensate all problemes due to drift of amb temperature
 

It is very bad idea to use RC oscillator as a frequency reference. Also, bad idea to measure capacitor AC resistance.
Listen thannara123. He speak a correct things.
 

here on my repositories you can get examples of capacitor (or resistance or inductance) measurments
using different methods, most of them are open source.
**broken link removed**
and
**broken link removed**
 
I am now trying to make An LCR methttps://www.circuitvalley.com/2011/08/accurate-lc-inductance-capacitance-meter.html#comment-form , I am getting some error when it simulating in proteus
only showing calibrating .
any body done this project .
Can anyone help me ?
I am attaching the proteus files

- - - Updated - - -

Capture.JPG I changed some resistor are connected wrongly but nothing happend
 

Attachments

  • LCR.rar
    42.7 KB · Views: 56

Can you insert lines in the program to have it tell you what step it is doing?

"Setting to zero"
"Starting count"
"Starting routine 1"
"Reading sense wire"
"selecting range"
Etc?
 

Sir I haven't source Program I have only Hex code .:-?
 
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