#include <Wire.h>
#include <LiquidCrystal_I2C.h>

LiquidCrystal_I2C lcd(0x27, 16, 2);
const int signalPin = A1;

void setup() {
  // put your setup code here, to run once:
  lcd.init(); lcd.backlight();
  pinMode(signalPin, INPUT);
  lcd.setCursor(0, 0);  lcd.print("Freq Counter");
}

void loop() {
  // put your main code here, to run repeatedly:
  //測量高電位與低電位的持續時間（單位：微秒 uS)
  unsigned long hightime = pulseIn(signalPin, HIGH, 1000000);
  unsigned long lowtime  = pulseIn(signalPin, LOW, 1000000);
  //周期=高電位時間＋低電位時間
  unsigned long period = hightime + lowtime ;

  float frequency = 0 ;

  if (period > 0){
    frequency = 1000000.0 / period;  //頻率 = 1 / 週期
  }
  lcd.setCursor(0,1);lcd.print("Freq:");

  if (hightime == 0 || lowtime == 0){
    lcd.print("0.00 Hz     ");  //沒訊號顯示 0
  } else {
    lcd.print(frequency, 2);lcd.print("Hz   "); //有訊號顯示頻率
  }
  delay(300);
}