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

@@ -1,34 +1,58 @@
 /*
- * 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.
+  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
+ attached to the sensor pin.
+ 
+ The sensor minumum and maximum initial values may seem backwards.
+ Initially, you set the minimum high and listen for anything 
+ lower, saving it as the new minumum. Likewise, you set the
+ maximum low and listen for anything higher as the new maximum.
+ 
+ The circuit:
+ * Analog sensor (potentiometer will do) attached to analog input 0
+ * LED attached from digital pin 9 to ground
+ 
+ created 29 Oct 2008
+ By David A Mellis
+ Modified 17 Jun 2009
+ By Tom Igoe
+ 
+ http://arduino.cc/en/Tutorial/Calibration
+ 
  */
 
-int sensorPin = 2;
-int ledPin = 9;
+// These constants won't change:
+const int sensorPin = 2;     // pin that the sensor is attached to
+const int ledPin = 9;        // pin that the LED is attached to
+
+const int sensorMin = 1023;  // minimum sensor value
+const int sensorMax = 0;     // maximum sensor value
+
+// variables:
+int sensorValue = 0;         // the sensor value
+
 
-int val = 0;
-int sensorMin = 1023, sensorMax = 0;
 
 void setup() {
-  // signal the start of the calibration period
+  // turn on LED to 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);
+    sensorValue = analogRead(sensorPin);
 
     // record the maximum sensor value
-    if (val > sensorMax) {
-      sensorMax = val;
+    if (sensorValue > sensorMax) {
+      sensorMax = sensorValue;
     }
 
     // record the minimum sensor value
-    if (val < sensorMin) {
-      sensorMin = val;
+    if (sensorValue < sensorMin) {
+      sensorMin = sensorValue;
     }
   }
 
@@ -37,13 +61,15 @@ void setup() {
 }
 
 void loop() {
-  val = analogRead(sensorPin);
+  // read the sensor:
+  sensorValue = analogRead(sensorPin);
 
   // apply the calibration to the sensor reading
-  val = map(val, sensorMin, sensorMax, 0, 255);
+  sensorValue = map(sensorValue, sensorMin, sensorMax, 0, 255);
 
   // in case the sensor value is outside the range seen during calibration
-  val = constrain(val, 0, 255);
+  sensorValue = constrain(sensorValue, 0, 255);
 
-  analogWrite(ledPin, val);
+  // fade the LED using the calibrated value:
+  analogWrite(ledPin, sensorValue);
 }