Add audio example 2 (loopback)

Author: sfe-SparkFro

examples/Audio_Examples/AudioExample2_Loopback/AudioExample2_Loopback.ino

@@ -0,0 +1,71 @@
+#include "SparkFun_u-blox_Cellular_Arduino_Library.h"
+
+// Uncomment the line below that you need for Serial on your platform
+#define mySerial Serial1
+// SoftwareSerial mySerial(16, 17);
+
+// Uncomment the module you're using. If your module is not listed below, then
+// it's not supported for this example
+UBX_CELL_VOICE_BASE myModule; // This example works with all voice-enabled modules, so this base class can be used
+// LARA_R6001 myModule;
+// LARA_R6401 myModule;
+// LARA_R6801_00B myModule;
+
+void setup()
+{
+  Serial.begin(115200); // Start the serial console
+
+  // Wait for user to press key to begin
+  Serial.println(F("u-blox Cellular Audio Example 2 - Loopback"));
+
+  Serial.println();
+  Serial.println(F("!!!!!!!! ATTENTION !!!!!!!! ATTENTION !!!!!!!! ATTENTION !!!!!!!!"));
+  Serial.println(F("This example requires an audio codec attached to the I2S interface"));
+  Serial.println(F("of the cellular modem. Please add one and update this example as"));
+  Serial.println(F("needed to configure your audio codec!"));
+  Serial.println(F("!!!!!!!! ATTENTION !!!!!!!! ATTENTION !!!!!!!! ATTENTION !!!!!!!!"));
+  Serial.println();
+
+  Serial.println(F("Press any key to begin"));
+  
+  while (!Serial.available()) // Wait for the user to press a key (send any serial character)
+    ;
+  while (Serial.available()) // Empty the serial RX buffer
+    Serial.read();
+
+  Serial.println(F("Beginning..."));
+
+  // myModule.enableDebugging(); // Uncomment this line to enable helpful debug messages on Serial
+
+  // For the MicroMod Asset Tracker, we need to invert the power pin so it pulls high instead of low
+  // Uncomment the next line if required
+  // myModule.invertPowerPin(true); 
+
+  // Initialize the module
+  if (myModule.begin(mySerial, UBX_CELL_DEFAULT_BAUD_RATE) )
+  {
+    Serial.println(F("Module connected!"));
+  }
+  else
+  {
+    Serial.println(F("Unable to communicate with the module."));
+    Serial.println(F("Manually power-on (hold the module's On button for 3 seconds) and try again."));
+    while (1) ; // Loop forever on fail
+  }
+  Serial.println();
+}
+
+void loop()
+{
+  while(Serial.available() != 0){Serial.read();}
+  Serial.println(F("Enter any key to begin loopback"));
+  while(Serial.available() == 0){}
+  
+  myModule.playAudioResource(UBX_CELL_AUDIO_RESOURCE_LOOPBACK);
+  
+  while(Serial.available() != 0){Serial.read();}
+  Serial.println(F("Enter any key to stop loopback"));
+  while(Serial.available() == 0){}
+  
+  myModule.stopAudioResource(UBX_CELL_AUDIO_RESOURCE_LOOPBACK);
+}