Update example for PWM/PDM

Author: TMRh20

examples/Platforms/NRF52/NRF52_PDM_PWMTest/NRF52_PDM_PWMTest.ino

@@ -1,24 +1,27 @@
 #include <AutoAnalogAudio.h>
 AutoAnalog aaAudio;
 
-// REQUIRES MBed Enabled Core for NRF52 (XIAO 52840 Sense)
+#if defined(USE_TINYUSB)
+// Needed for Serial.print on non-MBED enabled or adafruit-based nRF52 cores
+#include "Adafruit_TinyUSB.h"
+#endif
 
 void setup() {
-  
-  //Startup the PDM Microphone and PWM(pseudo DAC) on pin 5
-  aaAudio.begin(1, 1);
-  aaAudio.autoAdjust = 0;
-  aaAudio.adcBitsPerSample = 16; // 16-bit audio at 16khz is the default on NRF52 and cannot be modified currently (in progress)
+  Serial.begin(115200);
+  aaAudio.begin(1, 1);  //Startup the PDM Microphone and PWM(pseudo DAC) on pin 5
+  aaAudio.adcBitsPerSample = 16;  // 16-bit audio at 16khz is the default on NRF52 and cannot be modified currently (in progress)
   aaAudio.dacBitsPerSample = 16;
   aaAudio.setSampleRate(16000);
-
 }
 
 void loop() {
 
-  aaAudio.getADC(320); // Get 320 Samples from the ADC
-  for (int i = 0; i < 320; i++) {  // Copy them into the DAC Buffer
-    aaAudio.dacBuffer16[i] = (uint16_t)(aaAudio.adcBuffer16[i]);
+  aaAudio.getADC(320);                        // Get 320 16-bit signed samples from the ADC
+  for (int i = 0; i < 320; i++) {             // Copy them into the DAC Buffer. The dac buffer is 16-bits unsigned
+    int16_t sample = aaAudio.adcBuffer16[i];  // Copy to signed 16-bit
+    sample += 0x8000;                         // Convert to unsigned 16-bit
+    aaAudio.dacBuffer16[i] = sample;          // Copy back to unsigned 16-bit buffer
+    aaAudio.dacBuffer16[i] >>= 6;             // Downsample to 10-bits for PWM output. With higher sample rates PWM can only handle 8-bits
   }
-  aaAudio.feedDAC(0,320); // Feed the DAC with the ADC data
+  aaAudio.feedDAC(0, 320);  // Feed the DAC with the ADC data
 }