Add SPH0645 microphone example

examples/HardwareTesting/Microphones/SPH0645/SPH0645.ino

+/* SPH0645 MEMS Microphone Test (Adafruit product #3421)
+ *
+ * Forum thread with connection details and other info:
+ * https://forum.pjrc.com/threads/60599?p=238070&viewfull=1#post238070
+ */
+
+
+#include <Audio.h>
+
+// GUItool: begin automatically generated code
+AudioInputI2S            i2s1;           //xy=180,111
+AudioFilterStateVariable filter1;        //xy=325,101
+AudioAmplifier           amp1;           //xy=470,93
+AudioAnalyzeFFT1024      fft1024_1;      //xy=616,102
+AudioConnection          patchCord1(i2s1, 0, filter1, 0);
+AudioConnection          patchCord2(filter1, 2, amp1, 0);
+AudioConnection          patchCord3(amp1, fft1024_1);
+// GUItool: end automatically generated code
+
+void setup() {
+  AudioMemory(50);
+  filter1.frequency(30); // filter out DC & extremely low frequencies
+  amp1.gain(8.5);        // amplify sign to useful range
+}
+
+void loop() {
+  if (fft1024_1.available()) {
+    // each time new FFT data is available
+    // print 20 bins to the Arduino Serial Monitor
+    Serial.print("FFT: ");
+    for (int i = 0; i < 20; i++) {
+      float n = fft1024_1.read(i);
+      if (n >= 0.001) {
+        Serial.print(n, 3);
+        Serial.print(" ");
+      } else {
+        Serial.print("  --  "); // don't print "0.000"
+      }
+    }
+    Serial.println();
+  }
+}