http://wordpress.codewrite.co.uk/pic/2014/01/21/cap-meter-with-arduino-uno/
const int OUT_PIN = A2;
const int IN_PIN = A0;
//Capacitance between IN_PIN and Ground
//Stray capacitance is always present. Extra capacitance can be added to
//allow higher capacitance to be measured.
const float IN_STRAY_CAP_TO_GND = 24.48; //initially this was 30.00
const float IN_EXTRA_CAP_TO_GND = 0.0;
const float IN_CAP_TO_GND = IN_STRAY_CAP_TO_GND + IN_EXTRA_CAP_TO_GND;
const int MAX_ADC_VALUE = 1023;
void setup()
{
pinMode(OUT_PIN, OUTPUT);
//digitalWrite(OUT_PIN, LOW); //This is the default state for outputs
pinMode(IN_PIN, OUTPUT);
//digitalWrite(IN_PIN, LOW);
Serial.begin(115200);
}
void loop()
{
//Capacitor under test between OUT_PIN and IN_PIN
//Rising high edge on OUT_PIN
pinMode(IN_PIN, INPUT);
digitalWrite(OUT_PIN, HIGH);
int val = analogRead(IN_PIN);
//Clear everything for next measurement
digitalWrite(OUT_PIN, LOW);
pinMode(IN_PIN, OUTPUT);
//Calculate and print result
float capacitance = (float)val * IN_CAP_TO_GND / (float)(MAX_ADC_VALUE - val);
Serial.print(F("Capacitance Value = "));
Serial.print(capacitance, 3);
Serial.print(F(" pF ("));
Serial.print(val);
Serial.println(F(") "));
while (millis() % 500 != 0)
;
}
