DIY Autoranging Capacitance Meter (10 pF–10 µF) – Easy Arduino Build

Necessary tools and machines

Soldering iron (generic)

Apps and online services

Arduino IDE

About this project

Simple Digital Multimeters (DMMs) cannot measure the capacitance and in order to find the capacitance, you either need to go for an advanced, expensive DMM or find a dedicated Capacitance modules.

In this project, I will build a simple Arduino Capacitance Meter with Auto-Ranging feature. It can measure capacitance from 10 pF to 10, 000 μF. The measurement takes place in automatic mode, it is enough to connect the capacitor to the measuring contacts. The device has two ranges: "nF" and "μF". When measuring a capacitor, the "nF" range is first switched on, if the capacitance is too large, then the transition to the "μF" range occurs.

Each capacitance meter has an RC circuit with known resistor values and an unknown capacitor value. The Arduino will measure the voltage at the capacitor and record the time it takes to reach a certain percentage of it’s voltage when fully charged (the time constant). Since the resistance value is already known, we can use the formula in a program that will calculate the unknown capacitance. The capacitor under test is charged using one of the resistors. The Arduino initiates the charging of the capacitor through resistor according to its capacity. In the capacitance meter, a zero calibration is performed every time it is turned on, therefore, at the moment of switching on, a capacitor should not be connected to the measuring contacts. Also, all capacitors must be pre-discharged.

The accuracy is +/- a few percent and depends primarily on the tolerance of the resistors used as well as the stability of the supply voltage.

Lastly, the entire device is housed in a suitable box and is another useful tool in your lab.

Code

• Arduino code

Arduino codeC/C++

#include <LiquidCrystal.h>
LiquidCrystal lcd(12, 11, 5, 4, 3, 2);// RS,E,D4,D5,D6,D7
void setup(){
  lcd.begin(16, 2);// LCD 16X2
  pinMode(A0,INPUT);
}
unsigned long time0,time1,time2; 
float c,null0;
byte kn,mk,i;

void loop(){ 
  lcd.setCursor(15,0); 
  lcd.print("*");
  if(mk==0){
    pinMode(8,OUTPUT);
    pinMode(7,INPUT);
    digitalWrite(8,HIGH);
  }

  if(mk==1){
    pinMode(7,OUTPUT);
    pinMode(8,INPUT);
    digitalWrite(7,HIGH);
  }

  time0=micros();
  while(analogRead(A0)<644){
    time2=micros()-time0;
    if(time2>=1000000 && mk==0){
      mk=1;
      time0=100000000;
      break;
    }
  }

  time1=micros()-time0; 

  while(analogRead(A0)>0){ 
    pinMode(7,OUTPUT); 
    pinMode(8,OUTPUT); 
    digitalWrite(7,LOW); 
    digitalWrite(8,LOW);
  }

  if(mk==1&&time1<1000){
    mk=0;
  }

  lcd.setCursor(1,0);
  c=time1;
  c=c/1000-null0;
  c=abs(c);

  if(time1>=10000000){
    lcd.setCursor(1,0);
    lcd.print(" TEST uF   "); 
  }
  else{
    lcd.print(c); 

    if(mk==0){
      lcd.print(" nF       ");
    }
    if(mk==1){
      lcd.print(" uF       ");
    }
  }
  if(i==0){
    i++;
    null0=c+0.02;
  }
  delay(100);
}

Schematics