Added arduino libs

libraries/PID/examples/PID_RelayOutput/PID_RelayOutput.ino

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+/********************************************************
+ * PID RelayOutput Example
+ * Same as basic example, except that this time, the output
+ * is going to a digital pin which (we presume) is controlling
+ * a relay.  the pid is designed to Output an analog value,
+ * but the relay can only be On/Off.
+ *
+ *   to connect them together we use "time proportioning
+ * control"  it's essentially a really slow version of PWM.
+ * first we decide on a window size (5000mS say.) we then
+ * set the pid to adjust its output between 0 and that window
+ * size.  lastly, we add some logic that translates the PID
+ * output into "Relay On Time" with the remainder of the
+ * window being "Relay Off Time"
+ ********************************************************/
+
+#include <PID_v1.h>
+
+#define PIN_INPUT 0
+#define RELAY_PIN 6
+
+//Define Variables we'll be connecting to
+double Setpoint, Input, Output;
+
+//Specify the links and initial tuning parameters
+double Kp=2, Ki=5, Kd=1;
+PID myPID(&Input, &Output, &Setpoint, Kp, Ki, Kd, DIRECT);
+
+int WindowSize = 5000;
+unsigned long windowStartTime;
+
+void setup()
+{
+  windowStartTime = millis();
+
+  //initialize the variables we're linked to
+  Setpoint = 100;
+
+  //tell the PID to range between 0 and the full window size
+  myPID.SetOutputLimits(0, WindowSize);
+
+  //turn the PID on
+  myPID.SetMode(AUTOMATIC);
+}
+
+void loop()
+{
+  Input = analogRead(PIN_INPUT);
+  myPID.Compute();
+
+  /************************************************
+   * turn the output pin on/off based on pid output
+   ************************************************/
+  if (millis() - windowStartTime > WindowSize)
+  { //time to shift the Relay Window
+    windowStartTime += WindowSize;
+  }
+  if (Output < millis() - windowStartTime) digitalWrite(RELAY_PIN, HIGH);
+  else digitalWrite(RELAY_PIN, LOW);
+
+}
+
+
+