Added explicit osc example

modules/simple-osc-explained/simple-osc-explained.ino

@@ -0,0 +1,45 @@
+/*
+ * 
+ * Simple (PWM) Oscillator Explained
+ * 
+  Instead of using the Tone() function, you can create a square wave oscillator by 
+  turning the digital pin 11 (speakerpin) on (HIGH) and off (LOW) very fast:
+  
+
+        |
+   HIGH |       ___      ___
+        |      |   |    |   |     50% duty cycle
+   LOW  |  ____|   |____|   |     (50% on, 50 off) Determined by delayMicroseconds()
+        |
+        |____________________
+                TIME
+
+ * 
+ * 
+ * 
+ * 
+ * 
+ */
+
+ 
+#define SPEAKER_PIN 11 
+
+void setup() {
+  // set pin 11 as output
+  pinMode(SPEAKER_PIN, OUTPUT);
+}
+
+void loop() {
+
+
+    digitalWrite( SPEAKER_PIN, LOW );
+    delayMicroseconds( analogRead(A2) ); // wait 
+    digitalWrite( SPEAKER_PIN, HIGH );
+    delayMicroseconds( analogRead(A2) ); // wait 
+
+  
+
+  //note: delayMircoseconds wont pause your whole code like normal delay() would do
+  //so, the code inside the while loop is executed simultaniously with the code in the
+  //main loop. See usage in simple-poly-osc.ino
+}