// Digital capacitor tester
// (C) 2013 Hackerstore, see https://www.hackerstore.nl/BlogArtikel/4
// update 2018 alexP
// See diagram cap-esr-freq.jpg for hardware connections.

#include <Wire.h>
#include <LiquidCrystal.h>
#define ANALOG_PIN  A5   // Analog pin for measuring. The value can be between 0 and 1023.
#define P1_PIN      12   // Pin for charging the capacitor via R9 & P1.
#define R8_PIN      7    // Pin for discharging the capacitor via R8.

float MicroFarad =0;
long tStart =0;
float nDuur =0;
int wait =2000;

LiquidCrystal lcd(13,11,6,4,3,2);

void setup() {
 pinMode(A4, INPUT_PULLUP); // button S3 connected for reset.
 pinMode(P1_PIN, OUTPUT);   // connection for charging the capacitor.
 digitalWrite(P1_PIN, LOW);  
 lcd.begin(16, 2);          // lcd screen with 2 rows with each 16 characters. 
}

void loop() {
 
 if(digitalRead(A4)== LOW)  // reset the software via button S3.
 {softReset();}
 
 Discharge();               // discharge the capacitor until zero voltage.
 
 /* 
 Measuring the value of the capacitor:
 Capacitance is a measure of the ability of a capacitor to store electrical charge. 
 The Arduino capacitance meter relies on the same basic property of capacitors: the time constant.
 The time constant of a capacitor is defined as the time it takes for the voltage
 across the capacitor to reach 63.2% of its voltage when fully charged. 
 An Arduino can measure capacitance because the time a capacitor takes to charge is
 directly related to its capacitance by the next equation: TC = R x C.
 TC is the time constant of the capacitor (in seconds).
 R is the resistance of the circuit (in Ohms).
 C is the capacitance of the capacitor (in Farads). 
 The formula to get the capacitance value in Farads is C = TC/R.
In this meter the R value can be set for calibration between 15kOhm and 25 kOhm via potmeter P1.
In the formula for the calculation a value of 22 kOhm is used. 
the full analog value on the ANALOG_PIN is 1023, so 63.2% is a value of 647.
*/
 
 lcd.setCursor(0,1);
 lcd.blink();                         // cursor blinks during measuring.
 digitalWrite(P1_PIN, HIGH);          // charge the capacitor. 
 tStart = millis();
 while(analogRead(ANALOG_PIN)<647){}; 
 nDuur = abs(millis()-tStart);
 MicroFarad = (nDuur/22000.0) * 1000; // calculate the value of the capacitor.  
 delay(wait);
 lcd.noBlink();

 // show the calculated value on the lcd screen:
 if(MicroFarad >= 1.0){
 // show the value in microFarad:
 lcd.clear();
 lcd.print("     ");
 lcd.print(MicroFarad,1); 
 lcd.print(" ");
 lcd.print((char)228);               // print the greek character mu.
 lcd.print("F ");
 delay(wait);
 }

 else{ 
 // show if no capacitor is connected or the value is too low to be accurate:
 if (MicroFarad < 0.07) {lcd.clear();
 lcd.print("  no capacitor");}
 // show the value in nanoFarad:
 else{ 
  lcd.clear();
  lcd.print("     ");
  lcd.print(MicroFarad*1000,1); 
  lcd.print(" ");
  lcd.print("nF ");
  delay(wait);
 }
 }
 }
// discharge the capacitor for the next measuring. 
void Discharge() { 
 digitalWrite(P1_PIN, LOW);            
 pinMode(R8_PIN, OUTPUT);           
 digitalWrite(R8_PIN, LOW);         
 while(analogRead(ANALOG_PIN)>0){} ;
 pinMode(R8_PIN, INPUT);
 delay(wait); 
    
}
// reset procedure
void softReset(){
 lcd.clear();
 lcd.setCursor(0,0);
 lcd.print("reset...");
 delay(wait);
 asm volatile ("  jmp 0");
}