Hello everyone, I have a question about the code found in the tutorial section of the site regarding a capacitance meter. The code is:
/* RCTiming_capacitance_meter
* Paul Badger 2008
* Demonstrates use of RC time constants to measure the value of a capacitor
*
* Theory A capcitor will charge, through a resistor, in one time constant, defined as T seconds where
* TC = R * C
*
* TC = time constant period in seconds
* R = resistance in ohms
* C = capacitance in farads (1 microfarad (ufd) = .0000001 farad = 10^-6 farads )
*
* The capacitor's voltage at one time constant is defined as 63.2% of the charging voltage.
*
* Hardware setup:
* Test Capacitor between common point and ground (positive side of an electrolytic capacitor to common)
* Test Resistor between chargePin and common point
* 220 ohm resistor between dischargePin and common point
* Wire between common point and analogPin (A/D input)
*/
#define analogPin 0 // analog pin for measuring capacitor voltage
#define chargePin 13 // pin to charge the capacitor - connected to one end of the charging resistor
#define dischargePin 11 // pin to discharge the capacitor
#define resistorValue 10000.0F // change this to whatever resistor value you are using
// F formatter tells compliler it's a floating point value
unsigned long startTime;
unsigned long elapsedTime;
float microFarads; // floating point variable to preserve precision, make calculations
float nanoFarads;
void setup(){
pinMode(chargePin, OUTPUT); // set chargePin to output
digitalWrite(chargePin, LOW);
Serial.begin(9600); // initialize serial transmission for debugging
}
void loop(){
digitalWrite(chargePin, HIGH); // set chargePin HIGH and capacitor charging
startTime = millis();
while(analogRead(analogPin) < 648){ // 647 is 63.2% of 1023, which corresponds to full-scale voltage
}
elapsedTime= millis() - startTime;
// convert milliseconds to seconds ( 10^-3 ) and Farads to microFarads ( 10^6 ), net 10^3 (1000)
microFarads = ((float)elapsedTime / resistorValue) * 1000;
Serial.print(elapsedTime); // print the value to serial port
Serial.print(" mS "); // print units and carriage return
if (microFarads > 1){
Serial.print((long)microFarads); // print the value to serial port
Serial.println(" microFarads"); // print units and carriage return
}
else
{
// if value is smaller than one microFarad, convert to nanoFarads (10^-9 Farad).
// This is a workaround because Serial.print will not print floats
nanoFarads = microFarads * 1000.0; // multiply by 1000 to convert to nanoFarads (10^-9 Farads)
Serial.print((long)nanoFarads); // print the value to serial port
Serial.println(" nanoFarads"); // print units and carriage return
}
/* dicharge the capacitor */
digitalWrite(chargePin, LOW); // set charge pin to LOW
pinMode(dischargePin, OUTPUT); // set discharge pin to output
digitalWrite(dischargePin, LOW); // set discharge pin LOW
while(analogRead(analogPin) > 0){ // wait until capacitor is completely discharged
}
pinMode(dischargePin, INPUT); // set discharge pin back to input
}
Particularly this bit
void loop(){
digitalWrite(chargePin, HIGH); // set chargePin HIGH and capacitor charging
startTime = millis();
while(analogRead(analogPin) < 648){ // 647 is 63.2% of 1023, which corresponds to full-scale voltage
}
elapsedTime= millis() - startTime;
// convert milliseconds to seconds ( 10^-3 ) and Farads to microFarads ( 10^6 ), net 10^3 (1000)
microFarads = ((float)elapsedTime / resistorValue) * 1000;
Serial.print(elapsedTime); // print the value to serial port
Serial.print(" mS "); // print units and carriage return
Can someone explain why the elapsed time bit is outside the {} for the while loop? Am I right in thinking that this means that analogRead is constantly reading until it's >= 648?
Could this also be done similar to:
while(analogRead(analogPin) < 648){
do something
}
if (analogRead(analogPin)>=648){
do something else
}
I'm not great at programming and i'm trying to understand this as i'm doing something similar but i'm not getting what I expect. I haven't posted it because it's for a uni project and would rather understand the issue so I can implement it.
