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應是DHT與 SoftwareSerial Library 相衝突
同時使用 
  mySerial.begin(9600); // PMS 3003 UART   //  Remark 後即OK
  dht.begin();
DHT 會Fail

#include <SoftwareSerial.h>
#include "DHT.h"
#define DHTPIN 2     // what digital pin we're connected to
// Uncomment whatever type you're using!
//#define DHTTYPE DHT11   // DHT 11
#define DHTTYPE DHT22   // DHT 22  (AM2302), AM2321

DHT dht(DHTPIN, DHTTYPE);
SoftwareSerial mySerial(0, 1); // RX, TX

void setup() {
  Serial.begin(57600);
  Serial.println("DHTxx test!");
 // mySerial.begin(9600); // PMS 3003 UART has baud rate 9600  //  Remark 後即OK
  dht.begin();
}

kotiger 回答了