ESP8266 NTP configTime

之前考統測時想要有一個能夠倒數幾天的機器，然而能夠準確的計時剩幾天就是一個大問題，所以決定使用帶有wifi功能的Nodemcu(使用Arduino IDE開發)來上網連接NTP網路對時，這樣就免去了去使用RTC時間晶片的不確定性，能夠更準確地來計時這樣。

首先我們需要用到<Time.h>模組，這裡詳細用法原理請直接參考

http://yhhuang1966.blogspot.com/2016/07/ntp-arduino.html

在GitHub下載涵式庫

https://github.com/PaulStoffregen/Time
這個程式寫法參照的出處
https://github.com/jumejume1/NodeMCU_ESP8266/blob/master/READ_TIME_FROM_INTERNET/READ_TIME_FROM_INTERNET.ino

!!!程式沒有閏年閏月修正功能!!!

#include <ESP8266WiFi.h>
#include <time.h>
#include <ESP8266WiFiMulti.h>
ESP8266WiFiMulti wifiMulti;
boolean connectioWasAlive = true;

int timezone = 8 * 3600;//時區+8(GMT+8)
int dst = 0;

boolean leap_year;
const int month_day[]={31,28,31,30,31,30,31,31,30,31,30,31};

const int leap_month_day[]={31,29,31,30,31,30,31,31,30,31,30,31};
int target[]={2019,5,31};//設定倒數日期
int date_now[3];

void setup() {
Serial.begin(115200);
Serial.println();
WiFi.mode(WIFI_STA);
WiFi.hostname("esp8266");
Serial.print("Wifi connecting ");
  wifiMulti.addAP("yourSSID","password");
  wifiMulti.addAP("your_second_SSID","second_password");//備用AP
  while(wifiMulti.run() != WL_CONNECTED){
    delay(100);
    Serial.print('.');
  }
  
Serial.printf(" connected to %s\n", WiFi.SSID().c_str());
Serial.println();
Serial.println("Wifi Connected Success!");
Serial.print("NodeMCU IP Address : ");
Serial.println(WiFi.localIP() );

configTime(timezone, dst, "pool.ntp.org","time.nist.gov");
Serial.println("\nWaiting for Internet time");
while(!time(nullptr)){
  Serial.print("*");
  delay(1000);
  }
Serial.println("\nTime response....OK");

}

void loop() {
monitorWiFi();
int days=0;
time_t now = time(nullptr);
struct tm* p_tm = localtime(&now);

  date_now[0]=p_tm->tm_year + 1900;           //今天幾年
  date_now[2]=p_tm->tm_mday;//今天幾號
  date_now[1]=p_tm->tm_mon + 1;               //今天幾月

   int months=((12+target[1])-date_now[1])%12;
  for(int i=0;i!=months;i++){                 //arr從零開始，扣1
    days=month_day[(date_now[1]+i-1)%12]+days;
  }

int number=days+target[2]-date_now[2];
   Serial.print(number);                      //剩幾天
}


void monitorWiFi(){                           //wifi連線設定
  wifiMulti.run(); 
  if (wifiMulti.run() != WL_CONNECTED){
    if (connectioWasAlive == true){
      connectioWasAlive = false;
      Serial.print("Looking for WiFi ");
    }
    Serial.print(".");
    delay(500);
  }
  else if (connectioWasAlive == false){
    connectioWasAlive = true;
    Serial.printf(" connected to %s\n", WiFi.SSID().c_str());
    Serial.print("IP address");
    Serial.println(WiFi.localIP());
  }
}