M5GO Base Analog Microphone

#include <SPI.h>  #include <SD.h>  #include <M5Unified.h>  // Pin definitions #define AIN_PIN 34 // Analog input pin for microphone signal #define SD_SPI_CS_PIN 4 // Chip Select pin for SD card SPI communication #define SD_SPI_SCK_PIN 18 // SPI Clock pin for SD card #define SD_SPI_MISO_PIN 19 // SPI MISO (Master In Slave Out) pin for SD card #define SD_SPI_MOSI_PIN 23 // SPI MOSI (Master Out Slave In) pin for SD card // Recording parameters constexpr size_t record_length = 512; // Number of samples per recording loop constexpr size_t record_samplerate = 12000; // Sampling frequency in Hertz (Hz) constexpr uint8_t bitsPerSample = 16; // Bit depth per audio sample constexpr uint8_t numChannels = 1; // Number of audio channels (1 = mono) static int16_t *rec_data; // Buffer to store current batch of samples static volatile bool isRecording = false; // Flag indicating recording state static size_t totalSamples = 0; // Total number of samples recorded unsigned long record_start_ms = 0; // Timestamp when recording started static int32_t w; // Display width (for UI positioning) // Structure defining the WAV file header format struct WavHeader { char riff[4]; // "RIFF" identifier (Resource Interchange File Format) uint32_t fileSize; // Total file size minus 8 bytes (size of RIFF chunk) char wave[4]; // "WAVE" identifier (specifies WAV format) char fmt[4]; // "fmt " identifier (format subchunk) uint32_t fmtSize; // Size of the format subchunk (16 for PCM) uint16_t format; // Audio format (1 = PCM, linear quantization) uint16_t channels; // Number of audio channels uint32_t sampleRate; // Sampling frequency in Hz uint32_t byteRate; // Byte rate (sampleRate * channels * bitsPerSample/8) uint16_t blockAlign; // Block alignment (channels * bitsPerSample/8) uint16_t bitsPerSample;// Number of bits per sample char data[4]; // "data" identifier (data subchunk) uint32_t dataSize; // Size of the audio data in bytes }; /** * Writes the WAV file header to a file * @param file Reference to the open WAV file * @param pcmBytes Total size of the audio data in bytes */ void writeWavHeader(File &file, uint32_t pcmBytes) { WavHeader header; memcpy(header.riff, "RIFF", 4); // Set RIFF identifier header.fileSize = 36 + pcmBytes; // Calculate total file size memcpy(header.wave, "WAVE", 4); // Set WAVE identifier memcpy(header.fmt, "fmt ", 4); // Set format subchunk identifier header.fmtSize = 16; // PCM format subchunk size header.format = 1; // PCM format header.channels = numChannels; // Set number of channels header.sampleRate = record_samplerate; // Set sampling rate header.byteRate = record_samplerate * numChannels * (bitsPerSample / 8); // Calculate byte rate header.blockAlign = numChannels * (bitsPerSample / 8); // Calculate block alignment header.bitsPerSample = bitsPerSample; // Set bit depth memcpy(header.data, "data", 4); // Set data subchunk identifier header.dataSize = pcmBytes; // Set audio data size file.seek(0); // Move to start of file file.write((const uint8_t*)&header, sizeof(WavHeader)); // Write header data } File wavFile; // File object for the WAV recording void setup(void) { auto cfg = M5.config(); M5.begin(cfg); M5.Display.setRotation(1); w = M5.Display.width(); M5.Display.setTextDatum(top_center); M5.Display.setTextColor(TFT_BLACK, TFT_WHITE); M5.Display.setFont(&fonts::FreeSansBoldOblique9pt7b); SPI.begin(SD_SPI_SCK_PIN, SD_SPI_MISO_PIN, SD_SPI_MOSI_PIN, SD_SPI_CS_PIN); M5.Display.drawCenterString("SD Initializing...", w/2, 0); if (!SD.begin(SD_SPI_CS_PIN, SPI, 25000000)) { M5.Display.drawCenterString("SD Init Error!", w/2, 50); while (1); // Halt execution if SD card fails } else { M5.Display.drawCenterString("SD Ready", w/2, 30); } // Allocate memory buffer for audio samples with specific memory capabilities rec_data = (int16_t*)heap_caps_malloc(record_length * sizeof(int16_t), MALLOC_CAP_8BIT | MALLOC_CAP_32BIT); if (!rec_data) { // Check if memory allocation failed M5.Display.drawCenterString("Memory Alloc Error", w/2, 60); // Show error message while (1); // Halt execution if memory allocation fails } memset(rec_data, 0, record_length * sizeof(int16_t)); // Initialize buffer to zero M5.Display.clear(TFT_WHITE); M5.Display.drawCenterString("ADC Mic Recording Example", w/2, 10); M5.Display.drawCenterString("A:Start C:Stop", w/2, 45); M5.Display.drawCenterString("Start Stop", w/2, 210); } uint32_t previous_sample_us = 0; // Timestamp of previous sample (for rate control) // Calculate microseconds between samples to maintain target sampling rate const uint32_t sampling_interval_us = 1000000UL / record_samplerate; void loop(void) { M5.update(); // Start recording when Button A is pressed (and not already recording) if (M5.BtnA.wasClicked() && !isRecording) { M5.Display.fillRect(0, 110, w, 100, TFT_WHITE); isRecording = true; totalSamples = 0; // Delete existing recording file if it exists if (SD.exists("/recording.wav")) { SD.remove("/recording.wav"); M5.Display.drawCenterString("Old File Deleted", w/2, 80); } // Open new WAV file for writing wavFile = SD.open("/recording.wav", FILE_WRITE); if (!wavFile) { // Check if file creation failed M5.Display.drawCenterString("Create WAV File Error!", w/2, 100); isRecording = false; return; } writeWavHeader(wavFile, 0); // Write initial header (will be updated later) record_start_ms = millis(); // Record start time M5.Display.drawCenterString("Recording...", w/2, 160); delay(15); // Short delay to debounce button } // Stop recording when Button C is pressed (and currently recording) if (M5.BtnC.wasClicked() && isRecording) { isRecording = false; } // Main recording process - runs while recording is active if (isRecording && wavFile) { uint32_t now = micros(); // Get current time in microseconds int32_t sum = 0; // Accumulator for sample analysis (not used in output) // Collect record_length samples for (size_t i = 0; i < record_length; ++i) { // Wait until correct time for next sample (maintains sampling rate) while (micros() - now < i * sampling_interval_us) {} // Read analog value from microphone pin int adval = analogRead(AIN_PIN); // Convert 12-bit ADC value (0-4095) to 16-bit signed sample: // - Subtract 2048 to center around 0 (DC offset removal) // - Shift left by 4 bits to scale 12-bit range to 16-bit range rec_data[i] = (int16_t)((adval - 2048) << 4); sum += rec_data[i]; // Accumulate sample (for potential future use) } // Write collected samples to SD card size_t written = wavFile.write((const uint8_t*)rec_data, record_length * sizeof(int16_t)); totalSamples += record_length; // Update total sample count // Calculate and display recording status float sec = ((float)totalSamples) / record_samplerate; // Calculate recording time in seconds uint32_t pcmBytes = totalSamples * sizeof(int16_t); // Calculate total data size char info[64]; sprintf(info, "Time: %.2fs Size:%dKB", sec, pcmBytes/1024); M5.Display.drawCenterString(info, w/2, 110); } // Finalize recording when stopped if (!isRecording && wavFile) { uint32_t pcmBytes = totalSamples * sizeof(int16_t); // Calculate total data size writeWavHeader(wavFile, pcmBytes); // Update header with final data size wavFile.close(); wavFile = File(); // Display final recording information float sec = ((float)totalSamples) / record_samplerate; // Calculate total recording time char info[64]; sprintf(info, "New WAV Saved: %.2fs, %dKB", sec, pcmBytes/1024); M5.Display.drawCenterString(info, w/2, 160); delay(35); // Short delay for stability } }