Interrupt Ohm meter, resistance shown on LCD Display

Projects Programming
1

Hi,

I am simply trying to make an ohm meter inspired by the same setup and some of the code as in this link: How to make an Arduino Ohm Meter - Arduino Project Hub

R1 is a known resistance and I am measuring R2 as an unknown resistance.
For the unknown resistance I am using a component that changes resistance over time. How can I create an interrupt that makes the LCD display the measured resistance only when changing?

The script
#include<LiquidCrystal.h>
LiquidCrystal lcd(2,3,4,5,6,7);

int analogPin = 0;
int intensity = 60;
int raw = 0;
int Vin = 5;
float Vout = 0; // voltage drop across unknown resistor
float R1 = 220; //known resistor
float R2 = 0; // unknown resistor
float buffer = 0;

void setup() {

// lcd setup
analogWrite(12,intensity);
lcd.begin(16,2);

// interrupts using timer 0
noInterrupts(); // stop all interrupts

// set timer0 at interrupt 2 kHz
TCCR0A = 0; //register TCCR2A is set to 0
TCCR0B = 0; //register TCCR2B is set to 0
TCNT0 = 0; // initialize counter value to 0

//turn on CTC mode
TCCR0A |= (1 << WGM01); //

// set CS01 and CS00 bits for 64 prescaler
TCCR0B |= (1 << CS01) | (1 << CS00);

// enable timer compare interrupt
TIMSK0 |= (1 << OCIE0A);

interrupts(); // enable all interrupts

}

void loop(){
raw = analogRead(analogPin);
lcd.setCursor(0,1);
}

ISR(TIMER0_COMPA_vect){
if(raw!=raw){
buffer = raw * Vin;
Vout = (buffer)/1024.0;
buffer = (Vin/Vout)-1;
R2=R1*buffer;
lcd.print(R2);
}
}

The script so far only shows 0 on the LCD after uploading the script.

Thank you!
-Victoria

2

You don't need an interrupt; below an example for the approach (haven't looked at your code).

void loop()
{
  static int oldReading;
  
  int reading = analogRead(A0);
  if (oldReading != reading)
  {
    oldReading = reading;

    // update LCD here
    ...
    ...
  }
}
3

Thanks. Is there a way to do with an interrupt?

4

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