arduino - millis

add:http://arduino.cc/en/Reference/Millis
[popexizhi:作为DH2321芯片的替代，delay()之后发现millis，也可以try。看来还是多看eg有好处啊:)]

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Description

Returns the number of milliseconds since the Arduino board began running the current program. This number will overflow (go back to zero), after approximately 50 days.

[popexizhi:50days,这个是工业级别的证明吗？还最大max的溢出值范围:)好吧log计算都忘记了，也没算出来:)]

Parameters

None

Returns

Number of milliseconds since the program started (unsigned long)

[popexizhi: unsigned long 的逻辑范围是类型取值范围: 0~4294967295 即 0~（2的32次方-1），50days是180000000毫秒左右.上面的应该是工业级别的硬件范围，4294967295换算完是3.268年左右]

Example

unsigned long time;

void setup(){
  Serial.begin(9600);
}
void loop(){
  Serial.print("Time: ");
  time = millis();
  //prints time since program started
  Serial.println(time);
  // wait a second so as not to send massive amounts of data
  delay(1000);
}
[popexizhi：next 在串口中调试一下]

Tip:

Note that the parameter for millis is an unsigned long, errors may be generated if a programmer tries to do math with other datatypes such as ints.
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PS:
[popexizhi:测试8小时的Dome，调试一下硬件看看效果如何，]

unsigned long time;
unsigned long oldtime=8*3600*1000;

void setup(){
  Serial.begin(9600);
}
void loop(){
  Serial.print("Time: ");
  time = millis();
  //prints time since program started
  Serial.println(time);
  // wait a second so as not to send massive amounts of data
  delay(1000);
  if (time> oldtime){
    Serial.println("8 hours is start");

    //继电器操作位置
  }
}