So you mean to read 6ksps from adc 12bit per sample, should i set i2c sampling frequency to the 12x6 = 72khz ?From my notes, the sample rate you have to set for ADC acquisition on the current esp-idf is (actual_sample_rate)/(bits_per_sample).
here is a small test code , i think i2s driver is not reliable.No:
- The sample depth is the I2S sample depth you specify when initializing the driver, most likely you use 16bit/sample.
- You need to divide, so 6000 samples/s and 16 bit means 6000/16=375.
Code: Select all
#include <Arduino.h>
#include "freertos/FreeRTOS.h"
#include "freertos/event_groups.h"
#include "esp_log.h"
#include "driver/i2s.h"
#include "soc/syscon_reg.h"
#include "driver/adc.h"
#include "esp_wifi.h"
#include "esp_event_loop.h"
#include "nvs_flash.h"
uint32_t SAMPLE_RATE = 6000;
uint32_t NUM_SAMPLES = 1000;
static QueueHandle_t i2s_event_queue;
void setup(){
Serial.begin(115200);
Serial.printf("%d :",APB_CLK_FREQ);
i2s_config_t i2s_config ;
i2s_config.mode = i2s_mode_t(I2S_MODE_MASTER | I2S_MODE_RX | I2S_MODE_ADC_BUILT_IN);
i2s_config.sample_rate = SAMPLE_RATE;
i2s_config.dma_buf_len = NUM_SAMPLES;
i2s_config.channel_format = I2S_CHANNEL_FMT_ONLY_RIGHT;
i2s_config.bits_per_sample = I2S_BITS_PER_SAMPLE_16BIT;
i2s_config.use_apll = false,
i2s_config.communication_format = I2S_COMM_FORMAT_I2S;
i2s_config.intr_alloc_flags = ESP_INTR_FLAG_LEVEL1;
i2s_config.dma_buf_count = 2;
i2s_driver_install(I2S_NUM_0, &i2s_config, 1, &i2s_event_queue);
i2s_set_adc_mode(ADC_UNIT_1, ADC1_CHANNEL_0);
i2s_adc_enable(I2S_NUM_0);
}
void loop(){
uint16_t i2s_read_buff[NUM_SAMPLES];
system_event_t evt;
if (xQueueReceive(i2s_event_queue, &evt, portMAX_DELAY) == pdPASS) {
if (evt.event_id==2) {
i2s_read_bytes(I2S_NUM_0, (char*)i2s_read_buff,NUM_SAMPLES*2, portMAX_DELAY);
Serial.write(100);
}
}
}As reported in an earlier post in this thread, I have measured 9.5μs (including the time taken to store in an array). This agrees with the measurements made by PA1EJO (with averaging parameter set to 1).I tried running the example program of peripherals/adc and found that each conversion took about 40us.
That mean, a sampling speed of 25K Samples/second.
Is that really possible or I am being mistaken?
I found out by experimenting that I can read the adc’s at a much higher rate than 6k but that the data is garbage. If I sample vibration readings from a motor at say 4K sps, I get a peak at the correct frequency when I do an fft but if I sample at a higher rate than 6k, the peak is not at the correct frequency and the fft content is rubbish.
I guess the limit is due to the fact that, unlike Atmel microcontrollers, the ESP32 does not have a sample-and-hold circuit (that we know of).The bandwidth of the ADC just is more-or-less 6KHz if you want a linear frequency response.
I am working on a development module that will have (among other things) 7 ADC inputs capable of 12 bit @ 1Msps. I am just finishing the layout now and will post more information elsewhere, however if you are interested in a small ESP32 based module with this feature drop me a PM and i will keep you updated.