Martin Simpson / Mbed OS CMSIS_FFT_mbed_os_DAC

CMSIS libraries example to DAC output of NUCLEO boards (that have them e.g F429ZI) to an Oscilloscope to display frequency domain bins

Dependencies:   mbed-dsp

main.cpp@0:05e2c9ca68e2, 2018-04-13 (annotated)

Committer:
martinsimpson
Date:
Fri Apr 13 08:59:47 2018 +0000
Revision:
0:05e2c9ca68e2
1st Commit; FFT using CMSIS libraries to generate a DAC output to a front end of a basic Oscilloscope to obseverve a FFT scan with bins (see code for resolution)

Who changed what in which revision?

UserRevisionLine numberNew contents of line
martinsimpson 0:05e2c9ca68e2 1 #include "mbed.h"
martinsimpson 0:05e2c9ca68e2 2 /* Include arm_math.h mathematic functions */
martinsimpson 0:05e2c9ca68e2 3 #include "arm_math.h"
martinsimpson 0:05e2c9ca68e2 4 /* Include mbed-dsp libraries */
martinsimpson 0:05e2c9ca68e2 5 #include "arm_common_tables.h"
martinsimpson 0:05e2c9ca68e2 6 #include "arm_const_structs.h"
martinsimpson 0:05e2c9ca68e2 7 #include "math_helper.h"
martinsimpson 0:05e2c9ca68e2 8
martinsimpson 0:05e2c9ca68e2 9 /* FFT settings */
martinsimpson 0:05e2c9ca68e2 10 #define SAMPLES 512 /* 256 real party and 256 imaginary parts */
martinsimpson 0:05e2c9ca68e2 11 #define FFT_SIZE SAMPLES / 2 /* FFT size is always the same size as we have samples, so 256 in our case */
martinsimpson 0:05e2c9ca68e2 12
martinsimpson 0:05e2c9ca68e2 13 /* Global variables */
martinsimpson 0:05e2c9ca68e2 14 float32_t Input[SAMPLES];
martinsimpson 0:05e2c9ca68e2 15 float32_t Output[FFT_SIZE];
martinsimpson 0:05e2c9ca68e2 16 bool trig=0;
martinsimpson 0:05e2c9ca68e2 17 /* MBED class APIs */
martinsimpson 0:05e2c9ca68e2 18 DigitalOut myled(LED1);
martinsimpson 0:05e2c9ca68e2 19 AnalogIn myADC(A1);
martinsimpson 0:05e2c9ca68e2 20 AnalogOut myDAC(D13);
martinsimpson 0:05e2c9ca68e2 21 Serial pc(USBTX, USBRX);
martinsimpson 0:05e2c9ca68e2 22 Ticker timer;
martinsimpson 0:05e2c9ca68e2 23
martinsimpson 0:05e2c9ca68e2 24 void sample(){
martinsimpson 0:05e2c9ca68e2 25 trig=1;
martinsimpson 0:05e2c9ca68e2 26 }
martinsimpson 0:05e2c9ca68e2 27
martinsimpson 0:05e2c9ca68e2 28 int main() {
martinsimpson 0:05e2c9ca68e2 29
martinsimpson 0:05e2c9ca68e2 30 //arm_cfft_instance_f32 S; // ARM CFFT module
martinsimpson 0:05e2c9ca68e2 31 float maxValue; // Max FFT value is stored here
martinsimpson 0:05e2c9ca68e2 32 uint32_t maxIndex; // Index in Output array where max value is
martinsimpson 0:05e2c9ca68e2 33 bool once=0;
martinsimpson 0:05e2c9ca68e2 34 pc.baud(115200);
martinsimpson 0:05e2c9ca68e2 35 pc.printf("Starting FFT\r\n");
martinsimpson 0:05e2c9ca68e2 36 while(1) {
martinsimpson 0:05e2c9ca68e2 37 timer.attach_us(&sample,20); //20us 50KHz sampling rate
martinsimpson 0:05e2c9ca68e2 38 for (int i = 0; i < SAMPLES; i += 2) {
martinsimpson 0:05e2c9ca68e2 39 while (trig==0){}
martinsimpson 0:05e2c9ca68e2 40 trig=0;
martinsimpson 0:05e2c9ca68e2 41 Input[i] = myADC.read() - 0.5f; //Real part NB removing DC offset
martinsimpson 0:05e2c9ca68e2 42 Input[i + 1] = 0; //Imaginary Part set to zero
martinsimpson 0:05e2c9ca68e2 43 }
martinsimpson 0:05e2c9ca68e2 44 timer.detach();
martinsimpson 0:05e2c9ca68e2 45 // Init the Complex FFT module, intFlag = 0, doBitReverse = 1
martinsimpson 0:05e2c9ca68e2 46 //NB using predefined arm_cfft_sR_f32_lenXXX, in this case XXX is 256
martinsimpson 0:05e2c9ca68e2 47 arm_cfft_f32(&arm_cfft_sR_f32_len256, Input, 0, 1);
martinsimpson 0:05e2c9ca68e2 48
martinsimpson 0:05e2c9ca68e2 49 // Complex Magniture Module put results into Output(Half size of the Input)
martinsimpson 0:05e2c9ca68e2 50 arm_cmplx_mag_f32(Input, Output, FFT_SIZE);
martinsimpson 0:05e2c9ca68e2 51
martinsimpson 0:05e2c9ca68e2 52 //Calculates maxValue and returns corresponding value
martinsimpson 0:05e2c9ca68e2 53 arm_max_f32(Output, FFT_SIZE, &maxValue, &maxIndex);
martinsimpson 0:05e2c9ca68e2 54
martinsimpson 0:05e2c9ca68e2 55 if (once==0){
martinsimpson 0:05e2c9ca68e2 56 pc.printf("Maximum is %f\r\n",maxValue);
martinsimpson 0:05e2c9ca68e2 57 once = 1;
martinsimpson 0:05e2c9ca68e2 58 }
martinsimpson 0:05e2c9ca68e2 59
martinsimpson 0:05e2c9ca68e2 60 //maxValue /= 100.0f;
martinsimpson 0:05e2c9ca68e2 61
martinsimpson 0:05e2c9ca68e2 62 myDAC=1.0f; //SYNC Pulse to DAC Output
martinsimpson 0:05e2c9ca68e2 63 wait_us(20); //Used on Oscilliscope set trigger level to the highest
martinsimpson 0:05e2c9ca68e2 64 myDAC=0.0f; //point on this pulse (all FFT data will be scaled
martinsimpson 0:05e2c9ca68e2 65 //90% of Max Value
martinsimpson 0:05e2c9ca68e2 66
martinsimpson 0:05e2c9ca68e2 67 for (int i=0; i<FFT_SIZE/2 ; i++){
martinsimpson 0:05e2c9ca68e2 68 myDAC=(Output[i]/maxValue)*0.9f; // Scale to Max Value and scale to 90%
martinsimpson 0:05e2c9ca68e2 69 wait_us(10); //Each pulse of 10us is 50KHz/256 = 195Hz resolution
martinsimpson 0:05e2c9ca68e2 70 }
martinsimpson 0:05e2c9ca68e2 71 myDAC=0.0f;
martinsimpson 0:05e2c9ca68e2 72 }
martinsimpson 0:05e2c9ca68e2 73 }