Adding a calibration example and moving knock into the sensors folder.

build/shared/dist/examples/Analog/Calibration/Calibration.pde

@@ -0,0 +1,49 @@
+/*
+ * Calibration
+ *
+ * Demonstrates one techinque for calibrating sensor input.  The
+ * sensor readings during the first five seconds of the sketch
+ * execution define the minimum and maximum of expected values.
+ */
+
+int sensorPin = 2;
+int ledPin = 9;
+
+int val = 0;
+int sensorMin = 1023, sensorMax = 0;
+
+void setup() {
+  // signal the start of the calibration period
+  pinMode(13, OUTPUT);
+  digitalWrite(13, HIGH);
+  
+  // calibrate during the first five seconds 
+  while (millis() < 5000) {
+    val = analogRead(sensorPin);
+    
+    // record the maximum sensor value
+    if (val > sensorMax) {
+      sensorMax = val;
+    }
+    
+    // record the minimum sensor value
+    if (val < sensorMin) {
+      sensorMin = val;
+    }
+  }
+  
+  // signal the end of the calibration period
+  digitalWrite(13, LOW);
+}
+
+void loop() {
+  val = analogRead(sensorPin);
+  
+  // apply the calibration to the sensor reading
+  val = map(val, sensorMin, sensorMax, 0, 255);
+  
+  // in case the sensor value is outside the range seen during calibration
+  val = constrain(val, 0, 255);
+  
+  analogWrite(ledPin, val);
+}