pdm: first version of PDM library supporting Nano 33 BLE board

Author: maidnl

libraries/PDM/examples/PDMSerialPlotter/PDMSerialPlotter.ino

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+/*
+  Nano 33 BLE Microphone to Serial Plotter
+*/
+#include <PDM.h>
+
+#ifndef CONFIG_BOARD_ARDUINO_NANO_33_BLE
+#error "Only Nano 33 BLE board is currently supported by this library"
+#endif
+// default number of output channels
+// Nano 33 BLE only supports 1 channel
+static const char channels = 1;
+// default PCM output frequency
+static const int frequency = 16000;
+// Buffer to read samples into
+// For better performance set the user buffer dimension to the dimension
+// of the buffer used by PDM library this way
+short sampleBuffer[DEFAULT_PDM_BUFFER_SIZE];
+// Number of bytes read
+volatile int samplesRead;
+
+void setup() {
+	Serial.begin(115200);
+	while (!Serial)
+		;
+
+	// Configure the data receive callback
+	PDM.onReceive(onPDMdata);
+
+	// Initialize PDM:
+	// - one channel (Mono)
+	// - 16 kHz sample rate (Standard for voice)
+	if (!PDM.begin(channels, frequency)) {
+		Serial.println("Failed to start PDM!");
+		while (1)
+			;
+	}
+}
+
+void loop() {
+	// Wait for samples to be read
+	if (samplesRead) {
+
+		// Print samples to the serial monitor or plotter
+		for (int i = 0; i < samplesRead; i++) {
+			if (channels == 2) {
+				Serial.print("L:");
+				Serial.print(sampleBuffer[i]);
+				Serial.print(" R:");
+				i++;
+			}
+			Serial.println(sampleBuffer[i]);
+		}
+
+		// Clear the read count
+		samplesRead = 0;
+	}
+}
+
+// Callback function: Handling the PDM on receive event
+// The PDM library will call this callback function as soon as the internal
+// buffer is ready and can be read
+// It is user responsibility to read from PDM as fast as possible otherwise
+// data will be lost
+void onPDMdata() {
+	// Query the number of bytes available
+	int bytesAvailable = PDM.available();
+	// Read into the sample buffer
+	PDM.read(sampleBuffer, bytesAvailable);
+
+	// 16-bit, 2 bytes per sample
+	samplesRead = bytesAvailable / 2;
+}

libraries/PDM/examples/micRecorder/getWave.py

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+import serial
+import wave
+import struct
+import time
+
+# --- CONFIGURATION ---
+SERIAL_PORT = '/dev/ttyACM0'  # CHECK YOUR ARDUINO IDE FOR THE CORRECT PORT!
+BAUD_RATE = 115200
+OUTPUT_FILENAME = "recording.wav"
+RECORD_SECONDS = 5     # How long to record
+SAMPLE_RATE = 16000    # Must match Arduino sketch
+# ---------------------
+
+def record_audio():
+    try:
+        ser = serial.Serial(SERIAL_PORT, BAUD_RATE)
+        print(f"Connected to {SERIAL_PORT}. Recording for {RECORD_SECONDS} seconds...")
+        
+        # Clear buffer to avoid old data
+        ser.reset_input_buffer()
+        
+        audio_frames = []
+        start_time = time.time()
+        
+        # Calculate how many bytes we expect
+        # 16000 samples/sec * 2 bytes/sample * seconds
+        total_bytes = SAMPLE_RATE * 2 * RECORD_SECONDS
+        bytes_received = 0
+        
+        while bytes_received < total_bytes:
+            if ser.in_waiting > 0:
+                # Read whatever is available
+                data = ser.read(ser.in_waiting)
+                audio_frames.append(data)
+                bytes_received += len(data)
+                
+                # Simple progress indicator
+                print(f"Recorded: {bytes_received} / {total_bytes} bytes", end='\r')
+
+        print("\nRecording complete. Saving...")
+        ser.close()
+
+        # Save to WAV file
+        with wave.open(OUTPUT_FILENAME, 'wb') as wf:
+            wf.setnchannels(1)      # Mono
+            wf.setsampwidth(2)      # 16-bit (2 bytes)
+            wf.setframerate(SAMPLE_RATE)
+            wf.writeframes(b''.join(audio_frames))
+            
+        print(f"File saved: {OUTPUT_FILENAME}")
+        
+    except serial.SerialException:
+        print(f"Error: Could not open port {SERIAL_PORT}. Is the Arduino Monitor open? Close it!")
+    except Exception as e:
+        print(f"An error occurred: {e}")
+
+if __name__ == "__main__":
+    record_audio()

libraries/PDM/examples/micRecorder/micRecorder.ino

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+/*
+  Nano 33 BLE Microphone to Serial Streamer
+
+  How to use this example
+  -----------------------
+
+  Download this sketch into the Nano33 BLE
+  This will start immediately mic acquisition
+  Be sure that serial monitor or any other program is not accessing the Nano33
+  serial port
+  Start the python script present in the same folder (getWawe.py)
+  This python script will get the data streamed by this sketch in the
+  serial port and pack them into a wav file you can listen with any player on
+  your PC
+  NOTE:
+  the python script uses /dev/ttyACM0 as default serial device, change it
+  accordingly if the nano33 serial does not correspond to this device
+  NOTE: the python script only records about 5 seconds of sounds
+*/
+#include <PDM.h>
+
+#ifndef CONFIG_BOARD_ARDUINO_NANO_33_BLE
+#error "Only Nano 33 BLE board is currently supported by this library"
+#endif
+
+// default number of output channels
+static const char channels = 1;
+// default PCM output frequency
+static const int frequency = 16000;
+// Buffer to read samples into
+// For better performance set the user buffer dimension to the dimension
+// of the buffer used by PDM library this way
+short sampleBuffer[DEFAULT_PDM_BUFFER_SIZE];
+// Number of bytes read
+volatile int samplesRead;
+
+void setup() {
+	Serial.begin(115200);
+	while (!Serial)
+		;
+
+	// Configure the data receive callback
+	PDM.onReceive(onPDMdata);
+
+	// Initialize PDM:
+	// - one channel (Mono)
+	// - 16 kHz sample rate (Standard for voice)
+	if (!PDM.begin(channels, frequency)) {
+		Serial.println("Failed to start PDM!");
+		while (1)
+			;
+	}
+}
+
+void loop() {
+	// Wait for samples to be read
+	if (samplesRead) {
+
+		// Write the raw bytes to the Serial port
+		// We send byte-by-byte to keep it fast and binary
+		Serial.write((uint8_t *)sampleBuffer, samplesRead * 2);
+		// Clear the read count
+		samplesRead = 0;
+	}
+}
+
+// Callback function: Handling the PDM on receive event
+// The PDM library will call this callback function as soon as the internal
+// buffer is ready and can be read
+// It is user responsibility to read from PDM as fast as possible otherwise
+// data will be lost
+void onPDMdata() {
+	// Query the number of bytes available
+	int bytesAvailable = PDM.available();
+	// Read into the sample buffer
+	PDM.read(sampleBuffer, bytesAvailable);
+
+	// 16-bit, 2 bytes per sample
+	samplesRead = bytesAvailable / 2;
+}

libraries/PDM/keywords.txt

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+#######################################
+# Syntax Coloring Map PDM
+#######################################
+
+#######################################
+# Datatypes (KEYWORD1)
+#######################################
+
+PDM	KEYWORD1
+
+#######################################
+# Methods and Functions (KEYWORD2)
+#######################################
+begin	KEYWORD2
+end	KEYWORD2
+
+available	KEYWORD2
+read	KEYWORD2
+
+onReceive	KEYWORD2
+
+setGain	KEYWORD2
+setBufferSize	KEYWORD2
+
+#######################################
+# Constants (LITERAL1)
+#######################################

libraries/PDM/library.properties

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+name=PDM
+version=1.0
+author=Arduino
+maintainer=Arduino <info@arduino.cc>
+sentence=Enables the communication with devices that use the PDM Bus
+paragraph=
+category=Communication
+url=
+architectures=zephyr_main,zephyr_contrib
+includes=PDM.h