File content as of revision 1:7c6c1f98b8f5:

#include "mbed.h"
#include "N5110.h"

extern "C" void fftR4(short *y, short *x, int N);

float magnitude(short y1, short y2);
void updateSamples();
void doFFT();
void printSpectrum();
void printSamples();
void ledBarGraph();
void lcdEqualiser();
int calcPeakFrequency();

AnalogIn audio(p17);  // ADC pin must be biased at Vcc/2 using coupling capacitor and potential divider
BusOut leds(LED1,LED2,LED3,LED4);
LocalFileSystem local("local");               // Create the local filesystem under the name "local"
Serial serial(USBTX,USBRX);
//    VCC,SCE,RST,D/C,MOSI,SCLK,LED
N5110 lcd(p7,p8,p9,p10,p11,p13,p21);

#define BUF_LEN 1024
#define SAMP_FREQ 10000

short samples[BUF_LEN];  // store the values read from ADC
short mx[BUF_LEN*2]; // input data 16 bit, 4 byte aligned  x0r,x0i,x1r,x1i,....
short my[BUF_LEN*2]; // output data 16 bit,4 byte aligned  y0r,y0i,y1r,y1i,....
float spectrum[BUF_LEN/2];  // frequency spectrum

char buffer[14];  // screen buffer

int main()
{
    // initialise LCD and display welcomes message
    lcd.init();
    lcd.printString("Audio FFT",14,0);
    lcd.printString("Analyser",20,1);
    lcd.printString("Craig A. Evans",0,4);
    serial.baud(115200);
    leds = 15;
    wait(2.0);   // short pause to allow coupling capacitor to charge
    leds = 0;
    lcd.clear();

    while(1) {

        updateSamples();  // read in new analog values
        ledBarGraph();    // display amplitude bar graph on LEDs from sample values
        doFFT();          // calc FFT
        lcdEqualiser();   // plot spectrum on LCD

        //printSpectrum();
        //printSamples();
        //int tone = calcPeakFrequency();  // calculate peak frequcny and send over serial for debug
        //serial.printf("f = %u\n",tone);

        wait_ms(100);  // update display 100 ms

    }
}

void ledBarGraph()
{
    float rms = 0.0;  // initialse array
    for (int i = 0; i < BUF_LEN; i++) {
        rms+= samples[i]*samples[i];
    }
    // calc the sum of the squares
    
    rms/=BUF_LEN;     // get the mean
    rms = sqrt(rms);  // and root to get the RMS
    rms/= 16384.0;  // scale according to 16-bit signed maximum value

    // check value and update LEDs to show amplitude
    if (rms > 0.8) {
        leds = 15;
    } else if (rms > 0.6) {
        leds = 7;
    } else if (rms > 0.4) {
        leds = 3;
    } else if (rms > 0.2) {
        leds = 1;
    } else {
        leds = 0;
    }

    //serial.printf("RMS = %f\n",rms);
}

float magnitude(short y1, short y2)
{
    return sqrt(float(y1*y1+y2*y2));  // pythagoras
}

void updateSamples()
{
    for (int i = 0; i < BUF_LEN; i++) {
        samples[i] = (short) (audio.read_u16() - 0x8000);  // read unsigned 16-bit and convert to signed 16-bit (subtract 32768)
        wait_us(1e6/SAMP_FREQ);  // wait for sampling frequency, should really implement with tickers
    }
}

void doFFT()
{
    // clear buffers
    for (int i=0; i<2*BUF_LEN; i++) {
        my[i] = 0;
        mx[i] = 0;
    }

    for (int i=0; i<BUF_LEN; i++) { // load samples in array (skip imaginary input values)
        mx[i*2]=samples[i];
    }

    fftR4(my, mx, BUF_LEN);  // call FFT routine

    int j = 0;
    for (int i = 0; i < BUF_LEN; i+=2) {
        spectrum[j] = magnitude(my[i],my[i+1]);  // get magnitude of FFT output to get spectrum data
        j++;
    }
}

void printSpectrum()
{
    FILE *fp = fopen("/local/fft.csv","w");
    //now write a CSV file to filesytem of frequency vs amplitude
    int j = 0;
    for (int i = 0; i < BUF_LEN; i+=2) {
        int frequency = int(SAMP_FREQ/BUF_LEN/2*i);  // calculate value of frequency bin
        fprintf(fp, "%d,%f\n", frequency, spectrum[j]);
        j++;
    }
    fclose(fp);
}

void printSamples()
{
    FILE *fp = fopen("/local/samples.csv","w");
    //now write a CSV file to filesytem of frequency vs amplitude
    for (int i = 0; i < BUF_LEN; i++) {
        fprintf(fp, "%d\n", samples[i]);
    }
    fclose(fp);
}

int calcPeakFrequency()
{
    float max = 0.0;
    int frequency = 0;
    int j = 0;
    for (int i=0; i<BUF_LEN; i+=2) {  // loop through spectrum and look for maximum value
        if (spectrum[j] > max) {
            max = spectrum[j];
            frequency = int(SAMP_FREQ/BUF_LEN/2*i);  
        }
        j++;
    }
    //serial.printf("Max = %f\n",max);
    return frequency;
}

void lcdEqualiser()
{
    // spectrum has BUF_LEN/2 values = 512
    // screen has 84 pixel, giving 6 spectrum points per pixel

    float max = 0.0;  // used for normalisation later

    float pixelValue[84];

    for (int i=0; i<84; i++) {  // loop through array
        pixelValue[i] = 0.0;

        for (int y=0; y<6; y++) {
            pixelValue[i] += spectrum[i*6+y];  // sum the 6 values in the spectrum
        }
        pixelValue[i]/=6;  // calc. average for that pixel

        if (pixelValue[i] > max)  // check for biggest value
            max = pixelValue[i];
    }

    for (int i=0; i<84; i++) {  // loop through array
        pixelValue[i]/=max;  // normalise to 1.0
    }

    lcd.clear();
    for (int i=0; i<84; i++) {  // loop through array
        for (int j=0; j<= 47 - int(pixelValue[i]*47.0); j++) {  // loop through array
            lcd.setPixel(i,j);  // draw bar graphs for spectrum bins
        }
    }
    lcd.refresh();

}