#include <Servo.h>
#include <digitalWriteFast.h>
Servo myservo;
uint32_t startsecond;
uint32_t newsecond;
uint8_t pulses;

void setup() {
  Serial.begin(115200);
  myservo.write(90);       //center servo, ~1.5 ms pulse
  myservo.attach(2);       //servo on pin 2
  pulses = 0;              //start condition
  startsecond = millis();  //start condition
}

void loop() {
  /*
     for a one second period, count the number of pulses; have to
     do this the hard way, as we need to leave the pin as an output
  */
  newsecond = millis();
  if (newsecond - startsecond < 1000) { //if a second has not elapsed
    while (digitalReadFast(2) == LOW);        //  if pin is low, wait for high
    while (digitalReadFast(2) == HIGH);        //  if pin is high, wait for low
    pulses = pulses + 1;           //  increment counter
  }
  else {                                    //  else, disp value and restart timer, counter
    startsecond = newsecond;
    if (pulses != 50) Serial.println(pulses);
    pulses = 0;
  }
}