maxValue problem, Solved quickly

Projects Programming
1

Hi This is AC voltmeter which is using maxValue - minValue for calculating amplitude of AC signal, I want to add on LCD maxValue to be displayed,.
This is whot I did ( marked by +++++++++++ ) but M=0.00 all the time.
How to fix it ?

/*
  Measuring AC Current Using ACS712
  www.circuits4you.com
*/
#include <LiquidCrystal.h>
LiquidCrystal lcd(PA0, PA1, PA2, PA3, PA4, PA5);
const int sensorIn = PA7;
int mVperAmp = 185; // use 100 for 20A Module and 66 for 30A Module

double Voltage = 0;
double VRMS = 0;
double AmpsRMS = 0;

//+++++++++++++++++++++
double maxValue = 0;
//+++++++++++++++++++++

void setup() {
  Serial.begin(9600);
  lcd.begin(16, 2);
}

void loop() {

  Voltage = getVPP();
  VRMS = (Voltage / 2.0) * 0.707; //root 2 is 0.707
  AmpsRMS = (VRMS * 1000) / mVperAmp;
  Serial.print(AmpsRMS);
  Serial.println(" Amps RMS");

  lcd.setCursor(0, 1);
  lcd.print("U=");
  lcd.print(VRMS);
  
//++++++++++++++++++++++++
  lcd.setCursor(0, 0);
  lcd.print("M=");
  lcd.print(maxValue);
//++++++++++++++++++++++++

}

float getVPP()
{
  float result;
  int readValue;             //value read from the sensor
  int maxValue = 0;          // store max value here
  //int minValue = 1024;          // store min value here
  int minValue = 4095.0;

  uint32_t start_time = millis();
  while ((millis() - start_time) < 1000) //sample for 1 Sec
  {
    readValue = analogRead(sensorIn);
    // see if you have a new maxValue
    if (readValue > maxValue)
    {
      /*record the maximum sensor value*/
      maxValue = readValue;
    }
    if (readValue < minValue)
    {
      /*record the minimum sensor value*/
      minValue = readValue;
    }
  }

  // Subtract min from max
  //result = ((maxValue - minValue) * 5.0)/1024.0;
  result = ((maxValue - minValue) * 5.0) / 4095.0;

  return result;


}
2

You have two different variables called maxValue, one with global scope, and one with local scope - it is visible only in getVPP

Lose the "float" in front of the second one.

3 
 
float getVPP()
{
   result;
  int readValue;             //value read from the sensor
  int maxValue = 0;          // store max value here
  //int minValue = 1024;          // store min value here
  int minValue = 4095.0;

This way ?
Doesn't make a sens.

4

Sorry. "int" in front of maxValue.

Or change the global double into an int.

5

Thanks
it is working.

6

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