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Hi guys,

I've written some code for measuring frequency based on zero crossings. You can add the code to the EmonLib.cpp file. It basically works like this; first it searches for a zero crossing, after that it measures the time for 'x' zero crossings that passes. The 'x' is the amount of crossings you want to measure, the higher this value the more accurate it is. It searches only for positive values; by that I mean values greater than 2.5V (ADC > 512 and < 528). On the end the frequency is calculated. Here is the code to add to the EmonLib.cpp file. Make sure to adjust the EmonLib.h appropriately!

=============================================

void EnergyMonitor::calcF(int crossings)
{
boolean stf = false;
unsigned long first, second;
unsigned long delta = 0;

while(stf == false)                                   //wait for first crossing
{
  startF = analogRead(inPinV);                    //using the voltage waveform
  if ((startF > 512) && (startF < 520))
  {
   stf = true;  //check its within range
   first = millis();
   delay(4); //Make sure no second read is in this range
  }
}

stf = false;

for(int i = 0 ; i < crossings ; i++)
{
  while(stf == false)                                   //wait for next crossing
  {
   startF = analogRead(inPinV);                    //using the voltage waveform
   if ((startF > 512) && (startF < 528))
   {
    stf = true;
    second = millis();
    delta += (second - first); //Add time between crossings
    first = second;
    delay(4); //Make sure no second read is in this range
   }
  }
  stf = false;
}

frequency = (crossings / 2) / ((double)delta / 1000);
}

=============================================

The main file looks like this:

=============================================

#include "EmonLib.h"             // Include Emon Library
EnergyMonitor emon1;             // Create an instance

void setup()
{ 
  Serial.begin(38400);
 
  emon1.voltage(4, 200.8, 0.5);  // Voltage: input pin, calibration, phase_shift

void loop()
{ 
  emon1.calcF(50);     // 50 zero crossings
  float freq = emon1.frequency;
 
  Serial.print("Frequency: ");
  Serial.println(freq);
 
  delay(1000);
}

=============================================

Regards,

Mathieu