Add simple example to library.

examples/SimpleSin/SimpleSin.ino

@@ -0,0 +1,41 @@
+/* DDS
+ * Example: Simple Sin
+ * This is a simple example that outputs a sin 
+ * wave on pin 3.
+*/
+
+#define DDS_REFCLK_DEFAULT 9600
+#include <DDS.h>
+
+#define PWM_PIN 3
+
+DDS dds;
+
+void setup() {
+  pinMode(PWM_PIN, OUTPUT);
+  digitalWrite(PWM_PIN, LOW);
+  
+  dds.start();
+  dds.playWait(600, 3000);
+  dds.on();
+  //dds.setAmplitude(31);
+}
+
+void loop() {
+  dds.setFrequency(2200);
+}
+
+#ifdef DDS_USE_ONLY_TIMER2
+ISR(TIMER2_OVF_vect) {
+  dds.clockTick();
+}
+#else // Use the ADC timer instead
+ISR(ADC_vect) {
+  static unsigned char tcnt = 0;
+  TIFR1 = _BV(ICF1); // Clear the timer flag
+  if(++tcnt == 4) {
+    tcnt = 0;
+  }
+  dds.clockTick();
+}
+#endif