int kaiguan=7;
int led=3;
unsigned long geshi=20;
int reading=1;
int shangci=HIGH;
int flag = 0;
unsigned long lastshijian=0;
void setup() {
  Serial.begin(115200);
  pinMode(led, OUTPUT); 
  pinMode(kaiguan, INPUT_PULLUP);
}
void loop() {
  reading=digitalRead(kaiguan);
  if(shangci!=reading)
  {
    lastshijian=millis();
  }
  // Serial.print("lastshijian:");
  // Serial.println(lastshijian);
  // Serial.print("millis():");
  // Serial.println(millis());
  
  if(millis() - lastshijian > geshi)
  {
    if(flag!=reading)
    {
      flag=reading;
      if(flag==LOW)
      {
        // lastshijian=millis();
        // flag=reading;
        digitalWrite(led, !digitalRead(led));
      }
    }
  }
  shangci = reading;
}