Arduino Frequency Measurement Help

RE: http://forum.arduino.cc/index.php?topic=64219.0
RE: http://forum.arduino.cc/index.php?topic=557364.0

hello, I has been try this frequency counter code without using any library and It was really great.
But I face a few problem. Since I need to to another task while scanning the frequency.

I need to lock a certain frequency, if the frequency match with the target I need.
I need to do analogPrint (PWM). And this delay function make the PWM bounching.

Can anyone help me with this code?
How to modify it from “delay(sampleTime);” to using Millis?

Sorry for my bad english,

hello everyone, I has been try this frequency counter code without using any library and It was really great.
But I face the problem. Since I need to to another task while scanning the frequency.

I need to lock a certain frequency, if the frequency match with the target I need.
I need to do analogPrint (PWM). And this delay function make the PWM bounching.

Can anyone help me with this code?
How to modify it from “delay(sampleTime);” to using Millis?

// Frequency counter sketch, for measuring frequencies low enough to execute an interrupt for each cycle
// Connect the frequency source to the INT0 pin (digital pin 2 on an Arduino Uno)

volatile unsigned long firstPulseTime;
volatile unsigned long lastPulseTime;
volatile unsigned long numPulses;

void isr() {
  unsigned long now = micros();
  if (numPulses == 1)
  {
    firstPulseTime = now;
  }
  else
  {
    lastPulseTime = now;
  }
  ++numPulses;
}

void setup() {
  Serial.begin(19200);    // this is here so that we can print the result
  pinMode(3, OUTPUT);     // put a PWM signal on pin 3, then we can connect pin 3 to pin 2 to test the counter
  analogWrite(3, 128);
}

// Measure the frequency over the specified sample time in milliseconds, returning the frequency in Hz
float readFrequency (unsigned int sampleTime)
{
  numPulses = 0;                      // prime the system to start a new reading
  attachInterrupt(0, isr, RISING);    // enable the interrupt
  delay(sampleTime);
  detachInterrupt(0);
  return (numPulses < 3) ? 0 : (1000000.0 * (float)(numPulses - 2))/(float)(lastPulseTime - firstPulseTime);
}

void loop()
{
  float freq = readFrequency(1000);
  Serial.println(freq);
  delay(1000);
}

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