Hi all
I made a simple multi-tasking code to experiment with signals in a "realistic" (hopefully) way
The code
a) generate a signal by a DAC on one task
b) sample the signal on the ADC on the other task
It works reasonably well. Now on task b I wish to compute the FFT of the sampled signal. I use the arduinoFFT library, but unfortunately the FFT.majorPeak() always gives me twice the expected frequency.
In particular I have a const float signalFrequency = 100.0; and I always get 200.249745 and similar results can be obtained with other frequencies
Hereafter the code
#include "arduinoFFT.h"
// Define the DAC and ADC pins
const int dacPin = 25; // DAC1 (GPIO 25) for sinusoid output
const int adcPin = 34; // ADC1 (GPIO 34) for reading the sinusoid
// Parameters for the sine wave
const int amplitude = 100; // Amplitude of the sine wave (max 255 for 8-bit DAC)
const int offset = 128; // DC offset (middle of the DAC range)
const float signalFrequency = 100.0; // Frequency of the sine wave in Hz
const int sampleRate = 1000; // Sample
int samplingFrequencyADC = 1000;
const uint16_t samples = 1024;
// Task Handles
TaskHandle_t dacTaskHandle = NULL;
TaskHandle_t adcTaskHandle = NULL;
/*
These are the input and output vectors
Input vectors receive computed results from FFT
*/
double vReal[samples];
double vImag[samples];
/* Create FFT object */
ArduinoFFT<double> FFT = ArduinoFFT<double>(vReal, vImag, samples, samplingFrequencyADC);
// DAC task function
void dacTask(void *parameter) {
// Generate and output the sine wave on DAC
while (true) {
for (int i = 0; i < sampleRate; i++) {
int sineValue = (int)(amplitude * sin(2.0 * PI * signalFrequency * i / sampleRate) + offset);
dacWrite(dacPin, sineValue); // Write to DAC (8-bit value)
/*
Serial.print(">");
Serial.print("dac:");
Serial.println(sineValue);
*/
// portTICK_PERIOD_MS is the number of ticks per ms
// vTaskDelay Delay a task for a given number of ticks.
vTaskDelay(1.0/sampleRate*1000 * portTICK_PERIOD_MS);
}
}
}
void adcTask(void *parameter) {
int i = 0;
while (true) {
int adcValue = analogRead(adcPin); // Read the ADC value
/*
Serial.print(">");
Serial.print("adc:");
Serial.println(adcValue);
*/
if (i<samples){
vReal[i] = adcValue-512;
vImag[i] = 0.0;
i=i+1;
}
if (i==samples){
i=0;
FFT.windowing(FFTWindow::Hamming, FFTDirection::Forward); /* Weigh data */
FFT.compute(FFTDirection::Forward); /* Compute FFT */
FFT.complexToMagnitude(); /* Compute magnitudes */
double x = FFT.majorPeak();
Serial.println(x, 6);
}
// portTICK_PERIOD_MS is the number of ticks per ms
// vTaskDelay Delay a task for a given number of ticks.
vTaskDelay(1.0/samplingFrequencyADC*1000 * portTICK_PERIOD_MS);
}
}
void setup() {
Serial.begin(115200);
// Initialize DAC pin (GPIO 25)
dacWrite(dacPin, 0); // Initialize DAC with a low value
// Initialize ADC pin (GPIO 34)
analogReadResolution(10); // Set ADC resolution to 12 bits
analogSetAttenuation(ADC_11db); // Set ADC attenuation (default 0dB)
// Create DAC task
//xTaskCreate(dacTask, "DAC Task", 2048, NULL, 1, &dacTaskHandle);
xTaskCreatePinnedToCore(dacTask, "DAC Task", 2048, NULL, 1, &dacTaskHandle,0);
// Create ADC task
//xTaskCreate(adcTask, "ADC Task", 2048, NULL, 1, &adcTaskHandle);
xTaskCreatePinnedToCore(adcTask, "ADC Task", 2048, NULL, 1, &adcTaskHandle,1);
}
void loop() {
// Empty loop, as tasks handle everything
}
Any idea on the reasons of this behavior?
Thanks in advance, Andrea
