159 lines
6.3 KiB
C++
159 lines
6.3 KiB
C++
// Adafruit Circuit Playground microphone library
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// by Phil Burgess / Paint Your Dragon.
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// Fast Fourier transform section is derived from
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// ELM-ChaN FFT library (see comments in ffft.S).
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#include <Arduino.h>
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#include "Adafruit_CPlay_Mic.h"
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#define DC_OFFSET (1023 / 3)
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#define NOISE_THRESHOLD 3
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// -------------------------------------------------------------------------
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// Reads ADC for given interval (in milliseconds, 1-65535), returns max
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// deviation from DC_OFFSET (e.g. 0-341). Uses ADC free-run mode w/polling.
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// Any currently-installed ADC interrupt handler will be temporarily
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// disabled while this runs.
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int Adafruit_CPlay_Mic::peak(uint16_t ms) {
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uint8_t admux_save, adcsra_save, adcsrb_save, timsk0_save, channel;
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uint16_t i, nSamples;
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int16_t adc, adcMin, adcMax;
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nSamples = (9615L * ms + 500) / 1000;
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if(!nSamples) nSamples = 1;
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channel = analogPinToChannel(4); // Pin A4 to ADC channel
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admux_save = ADMUX; // Save ADC config registers
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adcsra_save = ADCSRA;
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adcsrb_save = ADCSRB;
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// Init ADC free-run mode; f = ( 8MHz/prescaler ) / 13 cycles/conversion
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ADCSRA = 0; // Stop ADC interrupt, if any
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ADMUX = _BV(REFS0) | channel; // Aref=AVcc, channel sel, right-adj
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ADCSRB = 0; // Free run mode, no high MUX bit
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ADCSRA = _BV(ADEN) | // ADC enable
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_BV(ADSC) | // ADC start
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_BV(ADATE) | // Auto trigger
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_BV(ADIF) | // Reset interrupt flag
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_BV(ADPS2) | _BV(ADPS1); // 64:1 / 13 = 9615 Hz
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// ADC conversion-ready bit is polled for each sample rather than using
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// an interrupt; avoids contention with application or other library
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// using ADC ISR for other things (there can be only one) while still
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// providing the speed & precise timing of free-run mode (a loop of
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// analogRead() won't get you that).
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adcMin = 1023;
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adcMax = 0;
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for(i=0; i<nSamples; i++) {
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while(!(ADCSRA & _BV(ADIF))); // Wait for ADC result
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adc = ADC; // 0-1023
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ADCSRA |= _BV(ADIF); // Clear bit
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if(adc < adcMin) adcMin = adc;
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if(adc > adcMax) adcMax = adc;
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}
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ADMUX = admux_save; // Restore ADC config
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ADCSRB = adcsrb_save;
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ADCSRA = adcsra_save;
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(void)analogRead(A4); // Purge residue from ADC register
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adcMin = abs(adcMin - DC_OFFSET);
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adcMax = abs(adcMax - DC_OFFSET);
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if(adcMin > DC_OFFSET) adcMin = DC_OFFSET;
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if(adcMax > DC_OFFSET) adcMax = DC_OFFSET;
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if(adcMin > adcMax) adcMax = adcMin;
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return adcMax;
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}
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// -------------------------------------------------------------------------
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// Captures ADC audio samples at maximum speed supported by 32u4 (9615 Hz).
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// Ostensibly for FFT code (below), but might have other uses. Uses ADC
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// free-run mode w/polling. Any currently-installed ADC interrupt handler
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// will be temporarily disabled while this runs. No other interrupts are
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// disabled; as long as interrupt handlers are minor (e.g. Timer/Counter 0
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// handling of millis() and micros()), this isn't likely to lose readings.
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void Adafruit_CPlay_Mic::capture(int16_t *buf, uint8_t nSamples) {
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uint8_t admux_save, adcsra_save, adcsrb_save, timsk0_save, channel;
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int16_t adc;
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channel = analogPinToChannel(4); // Pin A4 to ADC channel
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admux_save = ADMUX; // Save ADC config registers
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adcsra_save = ADCSRA;
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adcsrb_save = ADCSRB;
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// Init ADC free-run mode; f = ( 8MHz/prescaler ) / 13 cycles/conversion
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ADCSRA = 0; // Stop ADC interrupt, if any
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ADMUX = _BV(REFS0) | channel; // Aref=AVcc, channel sel, right-adj
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ADCSRB = 0; // Free run mode, no high MUX bit
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ADCSRA = _BV(ADEN) | // ADC enable
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_BV(ADSC) | // ADC start
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_BV(ADATE) | // Auto trigger
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_BV(ADIF) | // Reset interrupt flag
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_BV(ADPS2) | _BV(ADPS1); // 64:1 / 13 = 9615 Hz
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// ADC conversion-ready bit is polled for each sample rather than using
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// an interrupt; avoids contention with application or other library
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// using ADC ISR for other things (there can be only one) while still
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// providing the speed & precise timing of free-run mode (a loop of
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// analogRead() won't get you that).
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for(uint8_t i=0; i<nSamples; i++) {
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while(!(ADCSRA & _BV(ADIF))); // Wait for ADC result
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adc = ADC;
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ADCSRA |= _BV(ADIF); // Clear bit
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// FFT requires signed inputs; ADC output is unsigned. DC offset is
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// NOT 512 on Circuit Playground because it uses a 1.1V OpAmp input
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// as the midpoint, and may swing asymmetrically on the high side.
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// Sign-convert and then clip range to +/- DC_OFFSET.
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if(adc <= (DC_OFFSET - NOISE_THRESHOLD)) {
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adc -= DC_OFFSET;
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} else if(adc >= (DC_OFFSET + NOISE_THRESHOLD)) {
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adc -= DC_OFFSET;
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if(adc > (DC_OFFSET * 2)) adc = DC_OFFSET * 2;
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} else {
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adc = 0; // Below noise threshold
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}
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buf[i] = adc;
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}
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ADMUX = admux_save; // Restore ADC config
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ADCSRB = adcsrb_save;
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ADCSRA = adcsra_save;
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(void)analogRead(A4); // Purge residue from ADC register
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}
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// -------------------------------------------------------------------------
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// Performs one cycle of fast Fourier transform (FFT) with audio captured
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// from mic on A4. Output is 32 'bins,' each covering an equal range of
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// frequencies from 0 to 4800 Hz (i.e. 0-150 Hz, 150-300 Hz, 300-450, etc).
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// Needs about 450 bytes free RAM to operate.
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typedef struct {
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int16_t r;
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int16_t i;
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} complex_t;
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extern "C" { // In ffft.S
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void fft_input(const int16_t *, complex_t *),
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fft_execute(complex_t *),
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fft_output(complex_t *, uint16_t *);
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}
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void Adafruit_CPlay_Mic::fft(
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uint16_t *spectrum) { // Spectrum output buffer, uint16_t[32]
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if(spectrum) {
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int16_t capBuf[64]; // Audio capture buffer
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complex_t butterfly[64]; // FFT "butterfly" buffer
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capture(capBuf, 64); // Collect mic data into capBuf
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fft_input(capBuf, butterfly); // Samples -> complex #s
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fft_execute(butterfly); // Process complex data
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fft_output(butterfly, spectrum); // Complex -> spectrum (32 bins)
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}
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}
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