The PDM library allows you to use PDM (Pulse-density modulation) microphones, such as the on board MP34DT05 on the Arduino Nano 33 BLE Sense.
Available sample rates include:
- 16000, 20000, 25000, 31250, 33333, 40000, 41667, 50000, 62500
This is achieved by fully implementing all PDM options:
| NRF_PDM_FREQ | Ratio 80 | Ratio 64 |
|---|---|---|
| 1280 | 16000 | 20000 |
| 2000 | 25000 | 31250 |
| 2667 | 33333 | 41667 (actual 41671) |
| 3200 | 40000 | 50000 |
| 4000 | 50000 | 62500 |
Initialize the PDM interface.
PDM.begin(channels, sampleRate)
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
…
if (!PDM.begin(1, 16000)) {
Serial.println("Failed to start PDM!");
while (1);
}
setGain(0x50);
…De-initialize the PDM interface.
PDM.end()
None
Nothing
…
if (!PDM.begin(1, 16000)) {
Serial.println("Failed to start PDM!");
while (1);
}
// …
PDM.end();
…
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.
PDM.available()
None
The number of bytes available to read
…
// 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);
…Set the callback function that is called when new PDM data is ready to be read.
PDM.onReceive(callback)
callback: function that is called when new PDM data is ready to be read
Nothing
…
// 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;
}
…Set the gain value used by the PDM interface.
PDM.setGain(gain)
gain: gain value to use, 0 - 80 [hexadecimal 0x50] (0 - 255) , defaults to 20 if not specified.
Note: Must be set after the begin operation call.
Nothing
…
// 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);
}
// optionally set the gain, defaults to 20
PDM.setGain(30);
…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.
If 2 channels are used, 128 stereo samples are stored in 512 bytes, alternating left channel, right channel as signed int16 (short) pairs.
PDM.setBufferSize(size)
size: buffer size to use in bytes
Note: setBufferSize must be called before begin operation, to allocate memory to the buffer.
Nothing
…
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);
}
…