`[code]I am learning arduino and i want to measure capacitance and i am trying this using this respective program in an Arduino Duemilanove.`

The program is at the end of the mail.

i found this program in this link

http://arduino.cc/playground/Main/CapacitanceMeasurement

Now i have troubles understanding the program.

I'm using a 1uF capacitor and r = 10000 ohm, i.e. the program should give me an output of 10uF

q1) he is saying CAP_PIN = 14.

Which is the pin 14 is it the AREF ?

q2) What is the circuit diagram ?

This is what i did -

-I connected AERF to resistance.

- Resistance to capacitor

- Capacitor to ground.

- and again junction between resistance and capacitor to A(0), voltage divider.

q3) An arduino only gives values between 0 and 1023, so don't we need to scale the values using map function ?

I anyways ran the code using the mentioned circuit but it's giving me really arbit values. The code was made for capacitors having pF capacitance, since i'm measuring uF, do i need to make any changes ?

[code]#ifndef cbi

#define cbi(sfr, bit) (_SFR_BYTE(sfr) &= ~_BV(bit))

#endif

#ifndef sbi

#define sbi(sfr, bit) (_SFR_BYTE(sfr) |= _BV(bit))

#endif

#include <math.h>

#define CAP_PIN 14

/* fit e^(bx). Returns 1/b. Implementation of:

Weisstein, Eric W. "Least Squares Fitting--Exponential."

From MathWorld--A Wolfram Web Resource.

http://mathworld.wolfram.com/LeastSquaresFittingExponential.html

*/

double fit_exp(int *ys, int xstep, int n) {

double sumy = 0;

double sumxy = 0;

double sumxxy = 0;

double sumxylny;

double sumylny;

int i;

for(i=0;i<n;i++) {

int x = i*xstep;

double xy = x*ys[i];

double lny = log(ys[i]);

sumy += ys[i];

sumxy += xy;

sumxxy += x*xy;

sumxylny += xy*lny;

sumylny += ys[i]*lny;

}

//b = (sumy*sumxylny-sumxy*sumylny) / (sumy*sumxxy-sumxy*sumxy);

return (sumy*sumxxy-sumxy*sumxy) / (sumy*sumxylny-sumxy*sumylny);

}

void setup() {

int n = 10;

int values[n];

// Make ADC faster by setting AD prescale to 16

sbi(ADCSRA,ADPS2) ;

cbi(ADCSRA,ADPS1) ;

cbi(ADCSRA,ADPS0) ;

Serial.begin(9600) ;

//There's a capacitor between CAP_PIN and ground

digitalWrite(CAP_PIN, HIGH);

delay(2000);

;; //wait for the capacitor to charge

//CAP_PIN should be connected to ground with a known resistance

digitalWrite(CAP_PIN, LOW); //let the capacitor discharge

for (int i=0; i<n; i++) {

values[i] = analogRead(0); //one of these takes 16us

}

//After the capacitor discharges below adc resolution

//all we get are zeros. Toss out the zeroes so they won't

//skew the results.

for(int i=0; i<n; i++) {

if(values[i] == 0) {

n = i;

break;

}

}

//fit_exp returns 1/b = -RC in us. With R=100k, C = -RC/10 pF.

Serial.print("C (uF) = ");

Serial.println( -fit_exp(values, 16, n)/10000.0 );

}

void loop() {

}

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