add simple tone example

Author: sandeepmistry

libraries/I2S/examples/SimpleTone/SimpleTone.ino

@@ -0,0 +1,34 @@
+#include <I2S.h>
+
+const int frequency = 440; // frequency of square wave in Hz
+const int amplitude = 500; // amplitude of square wave
+const int sampleRate = 8000; // sample rate in Hz
+
+const int halfWavelength = (sampleRate / frequency); // half wavelength of square wave
+
+short sample = amplitude; // current sample value
+int count = 0;
+
+void setup() {
+  Serial.begin(9600);
+  Serial.println("I2S simple tone");
+
+  if (I2S.begin(I2S_PHILIPS_MODE, sampleRate, 16)) {
+    Serial.println("Failed to initialize I2S!");
+    while (1); // do nothing
+  }
+}
+
+void loop() {
+  if (count % halfWavelength == 0) {
+    // invert the sample every half wavelength count multiple to generate square wave
+    sample = -1 * sample;
+  }
+
+  // write the same sample twice, once for left and once for the right channel
+  I2S.write(sample);
+  I2S.write(sample);
+
+  // increment the counter for the next sample
+  count++;
+}