[MKC-177,178,293,294] Core library migration

content/learn/07.built-in-libraries/01.pdm/pdm.md

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+---
+title: PDM Library
+description: The PDM library allows you to use Pulse-density modulation microphones, found onboard the Nano RP2040 Connect & Nano 33 BLE Sense boards.
+author: 'Arduino'
+tags: [Microphone, PDM]
+---
+
+## Overview
+
+The PDM library allows you to use PDM ([Pulse-density modulation](https://en.wikipedia.org/wiki/Pulse-density_modulation)) microphones, such as the onboard MP34DT05 on the Arduino Nano 33 BLE Sense.
+
+To use this library:
+
+```
+#include <PDM.h>
+```
+
+The library takes care of the audio that will be accessible also through the [ArduinoSound](https://www.arduino.cc/en/Reference/ArduinoSound) library.
+
+
+## Functions
+
+### `begin()`
+
+#### Description
+
+Initialize the PDM interface.
+
+#### Syntax
+
+```
+PDM.begin(channels, sampleRate)
+
+```
+
+#### Parameters
+- channels: the number of channels, 1 for mono, 2 for stereo
+- sampleRate: the sample rate to use in Hz
+
+#### Returns
+1 on success, 0 on failure
+
+#### Example
+
+```
+  if (!PDM.begin(1, 16000)) {
+    Serial.println("Failed to start PDM!");
+    while (1);
+  }
+
+
+```
+
+### `end()`
+
+#### Description
+
+De-initialize the PDM interface.
+
+#### Syntax
+
+```
+PDM.end()
+
+```
+
+#### Parameters
+None
+
+#### Returns
+Nothing
+
+#### Example
+
+```
+  if (!PDM.begin(1, 16000)) {
+    Serial.println("Failed to start PDM!");
+    while (1);
+  }
+
+
+  // 
+
+  PDM.end();
+
+
+```
+
+### `available()`
+
+#### Description
+
+Get the number of bytes available for reading from the PDM interface. This is data that has already arrived and was stored in the PDM receive buffer.
+
+#### Syntax
+
+```
+PDM.available()
+
+```
+
+#### Parameters
+None
+
+#### Returns
+The number of bytes available to read
+
+#### Example
+
+```
+// buffer to read samples into, each sample is 16-bits
+short sampleBuffer[256];
+
+// number of samples read
+volatile int samplesRead;
+
+// 
+
+  // query the number of bytes available
+  int bytesAvailable = PDM.available();
+
+  // read into the sample buffer
+  PDM.read(sampleBuffer, bytesAvailable);
+
+
+```
+
+### `read()`
+
+#### Description
+
+Read data from the PDM into the specified buffer.
+
+#### Syntax
+
+```
+PDM.read(buffer, size)
+
+```
+
+#### Parameters
+- buffer: array to store the PDM data into
+- size: number of bytes to read
+
+#### Returns
+The number of bytes read
+
+#### Example
+
+```
+// buffer to read samples into, each sample is 16-bits
+short sampleBuffer[256];
+
+// number of samples read
+volatile int samplesRead;
+
+// 
+
+  // query the number of bytes available
+  int bytesAvailable = PDM.available();
+
+  // read into the sample buffer
+  Int bytesRead = PDM.read(sampleBuffer, bytesAvailable);
+
+  // 16-bit, 2 bytes per sample
+  samplesRead = bytesRead / 2;
+
+
+```
+
+### `onReceive()`
+
+#### Description
+
+Set the callback function that is called when new PDM data is ready to be read.
+
+#### Syntax
+
+```
+
+PDM.onReceive(callback)
+
+```
+
+#### Parameters
+callback: function that is called when new PDM data is ready to be read
+
+#### Returns
+Nothing
+
+#### Example
+
+```
+// buffer to read samples into, each sample is 16-bits
+short sampleBuffer[256];
+
+// number of samples read
+volatile int samplesRead;
+
+// 
+
+  // configure the data receive callback
+  PDM.onReceive(onPDMdata);
+
+  // initialize PDM with:
+  // - one channel (mono mode)
+  // - a 16 kHz sample rate
+  if (!PDM.begin(1, 16000)) {
+    Serial.println("Failed to start PDM!");
+    while (1);
+  }
+
+
+  // 
+
+void onPDMdata() {
+  // query the number of bytes available
+  int bytesAvailable = PDM.available();
+
+  // read into the sample buffer
+  Int bytesRead = PDM.read(sampleBuffer, bytesAvailable);
+
+  // 16-bit, 2 bytes per sample
+  samplesRead = bytesRead / 2;
+}
+
+
+
+```
+
+### `setGain()`
+
+#### Description
+
+Set the gain value used by the PDM interface.
+
+#### Syntax
+
+```
+PDM.setGain(gain)
+
+```
+
+#### Parameters
+gain: gain value to use, 0 - 255, defaults to 20 if not specified.
+
+#### Returns
+Nothing
+
+#### Example
+
+```
+  // optionally set the gain, defaults to 20
+  PDM.setGain(30);
+
+  // initialize PDM with:
+  // - one channel (mono mode)
+  // - a 16 kHz sample rate
+  if (!PDM.begin(1, 16000)) {
+    Serial.println("Failed to start PDM!");
+    while (1);
+  }
+
+
+
+```
+
+### `setBufferSize()`
+
+#### Description
+
+Set the buffer size (in bytes) used by the PDM interface. Must be called before PDM.begin(...), a default buffer size of 512 is used if not called. This is enough to hold 256 16-bit samples.
+
+#### Syntax
+
+```
+PDM.setBufferSize(size)
+
+```
+
+#### Parameters
+size: buffer size to use in bytes
+
+#### Returns
+Nothing
+
+#### Example
+
+```
+  PDM.setBufferSize(1024);
+
+  // initialize PDM with:
+  // - one channel (mono mode)
+  // - a 16 kHz sample rate
+  if (!PDM.begin(1, 16000)) {
+    Serial.println("Failed to start PDM!");
+    while (1);
+  }
+
+```