Digital Capacitance Meter Circuit Using Arduino

As you can see the circuit is very simple just a couple of resistors are needed to find the unknown capacitance.The 1K ohm is the known resistor value and the 220 ohm resistor utilized for discharging the capacitor while measurement process takes place.The Arduino sense the rising and decreasing voltage on pin A0 which is connected between 1K ohm and 220 ohm resistors.Please take care of the polarity if you are using polarized capacitors such as electrolytic.Program:
//-----------------Program developed by R.Girish------------------//
const int analogPin = A0;
const int chargePin = 7 ;
const int dischargePin = 6;
float resistorValue = 1000 // Value of known resistor in ohm
unsigned long startTime;
unsigned long elapsedTime;
float microFarads;
void setup()
{
Serial.begin(9600);
pinMode(chargePin, OUTPUT);
digitalWrite(chargePin, LOW);
}
void loop()
{
digitalWrite(chargePin, HIGH);
startTime = millis();
while(analogRead(analogPin) < 648){}
elapsedTime = millis() - startTime;
microFarads = ((float)elapsedTime / resistorValue) * 1000;
if (microFarads > 1)
{
Serial.print("Value = ");
Serial.print((long)microFarads);
Serial.println(" microFarads");
Serial.print("Elapsed Time = ");
Serial.print(elapsedTime);
Serial.println("mS");
Serial.println("--------------------------------");
}
else
{
Serial.println("Please connect Capacitor!");
delay(1000);
}
digitalWrite(chargePin, LOW);
pinMode(dischargePin, OUTPUT);
digitalWrite(dischargePin, LOW);
while(analogRead(analogPin) > 0) {}
pinMode(dischargePin, INPUT);
}
//-----------------Program developed by R.Girish------------------//

Upload the above code to Arduino with completed hardware setup, initially don’t connect the capacitor. Open the serial monitor; it says “Please connect capacitor”.

Now connect a capacitor, its capacitance will be displayed as illustrated below.

It also shows the time taken to reach 63.2% of the capacitor’s full charge voltage, which is shown as elapsed time.

Circuit diagram for LCD based capacitance meter:

The above schematic is connection between LCD display and Arduino. The 10K potentiometer is provided for adjusting the contrast of the display. Rest of the connections are self-explanatory.

The above circuit is exactly same as serial monitor based design; you just need to connect LCD display.

Program for LCD based capacitance meter:

//-----------------Program developed by R.Girish------------------//
#include<LiquidCrystal.h>
LiquidCrystal lcd(12,11,5,4,3,2);
const int analogPin = A0;
const int chargePin = 7 ;
const int dischargePin = 6;
float resistorValue = 1000; // Value of known resistor in ohm
unsigned long startTime;
unsigned long elapsedTime;
float microFarads;
void setup()
{
Serial.begin(9600);
lcd.begin(16,2);
pinMode(chargePin, OUTPUT);
digitalWrite(chargePin, LOW);
lcd.clear();
lcd.setCursor(0,0);
lcd.print(" CAPACITANCE");
lcd.setCursor(0,1);
lcd.print(" METER");
delay(1000);
}
void loop()
{
digitalWrite(chargePin, HIGH);
startTime = millis();
while(analogRead(analogPin) < 648){}
elapsedTime = millis() - startTime;
microFarads = ((float)elapsedTime / resistorValue) * 1000;
if (microFarads > 1)
{
lcd.clear();
lcd.setCursor(0,0);
lcd.print("Value = ");
lcd.print((long)microFarads);
lcd.print(" uF");
lcd.setCursor(0,1);
lcd.print("Elapsed:");
lcd.print(elapsedTime);
lcd.print(" mS");
delay(100);
}
else
{
lcd.clear();
lcd.setCursor(0,0);
lcd.print("Please connect");
lcd.setCursor(0,1);
lcd.print("capacitor !!!");
delay(500);
}
digitalWrite(chargePin, LOW);
pinMode(dischargePin, OUTPUT);
digitalWrite(dischargePin, LOW);
while(analogRead(analogPin) > 0) {}
pinMode(dischargePin, INPUT);
}
//-----------------Program developed by R.Girish------------------//

With the completed hardware setup upload the above code. Initially don’t connect the capacitor. The display shows “Please connect capacitor!!!” now you connect the capacitor. The display will show the capacitor’s value and elapsed time taken to reach 63.2% of full charge capacitor.

Author’s Prototype: