Looking for guidance in frequency measurement

Projects General Guidance
22

I read a bunch of posts asking why millis doesn't start at zero and how to reset it to 0, and I guess I misunderstood what I was reading as you're right, it reads zero upon each start and with a delay I get usable values.

I'm almost there I guess. My DMM says 20hz, however I took another example to try and read the frequency on an input pin and I have not implemented it correctly because it prints out "Hz: inf" .

[edit] I've tried a few variations and the only thing I can surmise is that pulseIn blocks the loop, as the hz drop from 20 to 0 on my meter when I use pulseIn?

unsigned long currentTimeStamp;
unsigned long serialLastWriteTimeStamp;

int Htime;              //integer for storing high time
int Ltime;                //integer for storing low time
float Ttime;            // integer for storing total time of a cycle
float f_frequency;        //storing frequency

void setup()
{
    Serial.begin(9600);
    while (!Serial)
    {
      ; // Wait for serial to connect
    }
    Serial.println("");
    delay(2000);
   
    Serial.println("Frequency Demo");

    pinMode(7,INPUT);
    pinMode(8, OUTPUT);

    currentTimeStamp = millis();
    serialLastWriteTimeStamp = millis();

}

void loop()
{
    currentTimeStamp = millis();
 
    digitalWrite(8, HIGH);
    delay(25);
    digitalWrite(8, LOW);
    delay(25);

    if (currentTimeStamp > serialLastWriteTimeStamp)
    {
        Htime=pulseIn(7,HIGH);      //read high time
        Ltime=pulseIn(7,LOW);        //read low time
        Ttime = Htime+Ltime;

        f_frequency=1000000/Ttime;    //getting frequency with Ttime is in Micro seconds
        Serial.print("Hz: "); Serial.println(f_frequency);
        serialLastWriteTimeStamp = (millis() + 1000);
    }
    
}