1. Input Devices

1. Input Devices

This week, we delved into the world of input devices. The XIAO ESP32S3, equipped with a Sense expansion board, features a camera interface and a microphone interface. Given that my final project is an intelligent glasses kit, I require a camera, a microphone, and a six-axis sensor.

1.1 Camera

The XIAO ESP32S3 utilizes a Parallel Camera interface, which requires the following pins:

• VSYNC: Frame synchronization signal, transitioning from low to high voltage at the start of each frame.
• HSYNC: Line synchronization signal, transitioning from low to high voltage at the start of each line.
• MCLK: Camera operating clock signal, providing the clock for the camera.
• PCLK: Pixel clock signal, synchronizing pixel data.
• D0-D7: Pixel data, an 8-bit parallel data bus.

I am using the OV2640 camera, which supports a resolution of up to 1600x1200.

The program, written in ESP-IDF, captures images and sends them via an HTTP server.

tip

All project code is open-source and available at the following link: Camera Example Code

#include <esp_log.h>
#include <esp_system.h>
#include <nvs_flash.h>
#include <sys/param.h>
#include <string.h>
#include <driver/i2c.h>

#include "freertos/FreeRTOS.h"
#include "freertos/task.h"

#include "esp_netif.h"
#include "nvs_flash.h"
#include "esp_wifi.h"
#include "esp_event.h"

#include "esp_camera.h"
#include "esp_http_server.h"
#include "esp_timer.h"

#include "iperf_cmd.h"

#include "console_wifi.h"

#define PART_BOUNDARY "123456789000000000000987654321"
static const char *_STREAM_CONTENT_TYPE = "multipart/x-mixed-replace;boundary=" PART_BOUNDARY;
static const char *_STREAM_BOUNDARY = "\r\n--" PART_BOUNDARY "\r\n";
static const char *_STREAM_PART = "Content-Type: image/jpeg\r\nContent-Length: %u\r\n\r\n";

#define TAG "main"

esp_err_t jpg_stream_httpd_handler(httpd_req_t *req)
{
    camera_fb_t *fb = NULL;
    esp_err_t res = ESP_OK;
    size_t _jpg_buf_len;
    uint8_t *_jpg_buf;
    char *part_buf[64];
    static int64_t last_frame = 0;
    if (!last_frame)
    {
        last_frame = esp_timer_get_time();
    }

    res = httpd_resp_set_type(req, _STREAM_CONTENT_TYPE);
    if (res != ESP_OK)
    {
        return res;
    }

    while (true)
    {
        fb = esp_camera_fb_get();
        if (!fb)
        {
            ESP_LOGE(TAG, "Camera capture failed");
            res = ESP_FAIL;
            break;
        }
        if (fb->format != PIXFORMAT_JPEG)
        {
            ESP_LOGI(TAG, "Converting JPEG...");
            bool jpeg_converted = frame2jpg(fb, 80, &_jpg_buf, &_jpg_buf_len);
            if (!jpeg_converted)
            {
                ESP_LOGE(TAG, "JPEG compression failed");
                esp_camera_fb_return(fb);
                res = ESP_FAIL;
            }
        }
        else
        {
            _jpg_buf_len = fb->len;
            _jpg_buf = fb->buf;
        }

        if (res == ESP_OK)
        {
            res = httpd_resp_send_chunk(req, _STREAM_BOUNDARY, strlen(_STREAM_BOUNDARY));
        }
        if (res == ESP_OK)
        {
            size_t hlen = snprintf((char *)part_buf, 64, _STREAM_PART, _jpg_buf_len);

            res = httpd_resp_send_chunk(req, (const char *)part_buf, hlen);
        }
        if (res == ESP_OK)
        {
            res = httpd_resp_send_chunk(req, (const char *)_jpg_buf, _jpg_buf_len);
        }
        if (fb->format != PIXFORMAT_JPEG)
        {
            free(_jpg_buf);
        }
        esp_camera_fb_return(fb);
        if (res != ESP_OK)
        {
            break;
        }
        int64_t fr_end = esp_timer_get_time();
        int64_t frame_time = fr_end - last_frame;
        last_frame = fr_end;
        frame_time /= 1000;
        ESP_LOGI(TAG, "MJPG: %luKB %lums (%.1ffps)", (uint32_t)(_jpg_buf_len / 1024), (uint32_t)frame_time, 1000.0 / (uint32_t)frame_time);
    }

    last_frame = 0;
    return res;
}

#define CAM_PIN_PWDN  -1
#define CAM_PIN_RESET -1

#define CAM_PIN_VSYNC 38
#define CAM_PIN_HREF  47
#define CAM_PIN_PCLK  13
#define CAM_PIN_XCLK  10

#define CAM_PIN_SIOD 40
#define CAM_PIN_SIOC 39

#define CAM_PIN_D0 15
#define CAM_PIN_D1 17
#define CAM_PIN_D2 18
#define CAM_PIN_D3 16
#define CAM_PIN_D4 14
#define CAM_PIN_D5 12
#define CAM_PIN_D6 11
#define CAM_PIN_D7 48

static camera_config_t camera_config = {
    .pin_pwdn = CAM_PIN_PWDN,
    .pin_reset = CAM_PIN_RESET,
    .pin_xclk = CAM_PIN_XCLK,
    .pin_sccb_sda = CAM_PIN_SIOD,
    .pin_sccb_scl = CAM_PIN_SIOC,

    .pin_d7 = CAM_PIN_D7,
    .pin_d6 = CAM_PIN_D6,
    .pin_d5 = CAM_PIN_D5,
    .pin_d4 = CAM_PIN_D4,
    .pin_d3 = CAM_PIN_D3,
    .pin_d2 = CAM_PIN_D2,
    .pin_d1 = CAM_PIN_D1,
    .pin_d0 = CAM_PIN_D0,
    .pin_vsync = CAM_PIN_VSYNC,
    .pin_href = CAM_PIN_HREF,
    .pin_pclk = CAM_PIN_PCLK,

    .xclk_freq_hz = 20000000,
    .ledc_timer = LEDC_TIMER_0,
    .ledc_channel = LEDC_CHANNEL_0,

    .frame_size = FRAMESIZE_VGA,

    .jpeg_quality = 12, // 0-63, for OV series camera sensors, lower number means higher quality
    .fb_count = 2,      // When jpeg mode is used, if fb_count more than one, the driver will work in continuous mode.
    .fb_location = CAMERA_FB_IN_PSRAM,
    .grab_mode = CAMERA_FB_IN_PSRAM,
};

void app_main(void)
{
    ESP_ERROR_CHECK(esp_netif_init());
    ESP_ERROR_CHECK(esp_event_loop_create_default());
    esp_err_t ret = nvs_flash_init(); // Initialize NVS
    if (ret == ESP_ERR_NVS_NO_FREE_PAGES || ret == ESP_ERR_NVS_NEW_VERSION_FOUND)
    {
        ESP_ERROR_CHECK(nvs_flash_erase());
        ret = nvs_flash_init();
    }

    ESP_ERROR_CHECK(esp_camera_init(&camera_config));

    sensor_t *sensor = esp_camera_sensor_get();
    // sensor->set_vflip(sensor, 1);
    sensor->set_hmirror(sensor, 1);

    httpd_handle_t server = NULL;
    httpd_config_t config = HTTPD_DEFAULT_CONFIG();

    /* Use the URI wildcard matching function in order to
     * allow the same handler to respond to multiple different
     * target URIs which match the wildcard scheme */
    config.uri_match_fn = httpd_uri_match_wildcard;

    ESP_LOGI(TAG, "Starting HTTP Server on port: '%d'", config.server_port);
    ESP_ERROR_CHECK(httpd_start(&server, &config));

    /* URI handler for getting uploaded files */
    httpd_uri_t stream = {
        .uri = "/stream", // Match all URIs of type /path/to/file
        .method = HTTP_GET,
        .handler = jpg_stream_httpd_handler,
        .user_ctx = NULL // Pass server data as context
    };

    httpd_register_uri_handler(server, &stream);
    uint32_t frame_time = 0;

    // Initialize console REPL
    ESP_ERROR_CHECK(console_cmd_init());

    ESP_ERROR_CHECK(console_cmd_wifi_register());

    // start console REPL
    ESP_ERROR_CHECK(console_cmd_start());
}

Compile and flash the program to the XIAO ESP32S3:

idf.py build
idf.py flash

Open the serial monitor:

idf.py monitor

Connect the device to the same network as your PC using the serial command. Then, enter the device's IP address and port number in a browser to view the live camera feed.

> wifi sta join <ssid> <password>

Enter http://<device-ip>:<port>/stream in the browser to view the live camera feed.

1.2 Microphone

The XIAO ESP32S3 utilizes a DMIC interface, which requires the following pins:

• CLK: Clock signal, synchronizing audio data.
• DATA: Audio data, 8-bit serial data.

The program captures audio and records it to an SD card.

tip

All project code is open-source and available at the following link: Microphone Recording Example Code

#include <stdio.h>
#include <string.h>
#include <math.h>
#include <sys/unistd.h>
#include <sys/stat.h>
#include "sdkconfig.h"
#include "esp_log.h"
#include "esp_err.h"
#include "esp_system.h"
#include "esp_vfs_fat.h"
#include "freertos/FreeRTOS.h"
#include "freertos/task.h"
#include "driver/i2s_pdm.h"
#include "driver/gpio.h"
#include "driver/spi_common.h"
#include "sdmmc_cmd.h"
#include "format_wav.h"
#include "mbedtls/base64.h"

static const char *TAG = "pdm_rec_example";

#define SPI_DMA_CHAN   SPI_DMA_CH_AUTO
#define NUM_CHANNELS   (1) // For mono recording only!
#define SD_MOUNT_POINT "/sdcard"
#define SAMPLE_SIZE    (CONFIG_EXAMPLE_BIT_SAMPLE * 1024)
#define BYTE_RATE      (CONFIG_EXAMPLE_SAMPLE_RATE * (CONFIG_EXAMPLE_BIT_SAMPLE / 8)) * NUM_CHANNELS

// When testing SD and SPI modes, keep in mind that once the card has been
// initialized in SPI mode, it can not be reinitialized in SD mode without
// toggling power to the card.
sdmmc_host_t host = SDSPI_HOST_DEFAULT();
sdmmc_card_t *card;
i2s_chan_handle_t rx_handle = NULL;

static int16_t i2s_readraw_buff[SAMPLE_SIZE];
size_t bytes_read;
const int WAVE_HEADER_SIZE = 44;

void mount_sdcard(void)
{
    esp_err_t ret;
    // Options for mounting the filesystem.
    // If format_if_mount_failed is set to true, SD card will be partitioned and
    // formatted in case when mounting fails.
    esp_vfs_fat_sdmmc_mount_config_t mount_config = { .format_if_mount_failed = true, .max_files = 5, .allocation_unit_size = 8 * 1024 };
    ESP_LOGI(TAG, "Initializing SD card");

    spi_bus_config_t bus_cfg = {
        .mosi_io_num = CONFIG_EXAMPLE_SPI_MOSI_GPIO,
        .miso_io_num = CONFIG_EXAMPLE_SPI_MISO_GPIO,
        .sclk_io_num = CONFIG_EXAMPLE_SPI_SCLK_GPIO,
        .quadwp_io_num = -1,
        .quadhd_io_num = -1,
        .max_transfer_sz = 4000,
    };
    ret = spi_bus_initialize(host.slot, &bus_cfg, SPI_DMA_CHAN);
    if (ret != ESP_OK)
    {
        ESP_LOGE(TAG, "Failed to initialize bus.");
        return;
    }

    // This initializes the slot without card detect (CD) and write protect (WP) signals.
    // Modify slot_config.gpio_cd and slot_config.gpio_wp if your board has these signals.
    sdspi_device_config_t slot_config = SDSPI_DEVICE_CONFIG_DEFAULT();
    slot_config.gpio_cs = CONFIG_EXAMPLE_SPI_CS_GPIO;
    slot_config.host_id = host.slot;

    ret = esp_vfs_fat_sdspi_mount(SD_MOUNT_POINT, &host, &slot_config, &mount_config, &card);

    if (ret != ESP_OK)
    {
        if (ret == ESP_FAIL)
        {
            ESP_LOGE(TAG, "Failed to mount filesystem.");
        }
        else
        {
            ESP_LOGE(TAG,
                "Failed to initialize the card (%s). "
                "Make sure SD card lines have pull-up resistors in place.",
                esp_err_to_name(ret));
        }
        return;
    }

    // Card has been initialized, print its properties
    sdmmc_card_print_info(stdout, card);
}

void record_wav(uint32_t rec_time)
{
    // Use POSIX and C standard library functions to work with files.
    int flash_wr_size = 0;
    ESP_LOGI(TAG, "Opening file");

    uint32_t flash_rec_time = BYTE_RATE * rec_time;
    const wav_header_t wav_header = WAV_HEADER_PCM_DEFAULT(flash_rec_time, 16, CONFIG_EXAMPLE_SAMPLE_RATE, 1);

    // First check if file exists before creating a new file.
    struct stat st;
    if (stat(SD_MOUNT_POINT "/record.wav", &st) == 0)
    {
        // Delete it if it exists
        unlink(SD_MOUNT_POINT "/record.wav");
    }

    // Create new WAV file
    FILE *f = fopen(SD_MOUNT_POINT "/record.wav", "a");
    if (f == NULL)
    {
        ESP_LOGE(TAG, "Failed to open file for writing");
        return;
    }

    // Write the header to the WAV file
    fwrite(&wav_header, sizeof(wav_header), 1, f);

    uint8_t *pcm_buff = malloc(128*1024);

    // Start recording
    while (flash_wr_size < flash_rec_time)
    {
        // Read the RAW samples from the microphone
        if (i2s_channel_read(rx_handle, (char *)i2s_readraw_buff, SAMPLE_SIZE, &bytes_read, 1000) == ESP_OK)
        {
            printf("%d [0] %d [1] %d [2] %d [3]%d ...\n",bytes_read, i2s_readraw_buff[0], i2s_readraw_buff[1], i2s_readraw_buff[2], i2s_readraw_buff[3]);
            memcpy(pcm_buff + flash_wr_size, i2s_readraw_buff, bytes_read);
            printf("[0] %d [1] %d [2] %d [3]%d...\n",pcm_buff[flash_wr_size], pcm_buff[flash_wr_size + 1], pcm_buff[flash_wr_size + 2], pcm_buff[flash_wr_size + 3]);
            // Write the samples to the WAV file
            fwrite(i2s_readraw_buff, bytes_read, 1, f);
            flash_wr_size += bytes_read;
        }
        else
        {
            printf("Read Failed!\n");
        }
    }

    uint8_t *base64_pcm = malloc(flash_wr_size * 2);
    size_t base64_size = 0;
    // Base64 encode the PCM data
    mbedtls_base64_encode(base64_pcm, flash_wr_size * 2, &base64_size, pcm_buff, flash_wr_size);
    base64_pcm[base64_size] = '\0';
    printf("Base64 encoded PCM data %d: %d\n",base64_size, flash_wr_size);
    printf("%s\n", base64_pcm);

    ESP_LOGI(TAG, "Recording done!");
    fclose(f);
    ESP_LOGI(TAG, "File written on SDCard");

    // All done, unmount partition and disable SPI peripheral
    esp_vfs_fat_sdcard_unmount(SD_MOUNT_POINT, card);
    ESP_LOGI(TAG, "Card unmounted");
    // Deinitialize the bus after all devices are removed
    spi_bus_free(host.slot);
}

void init_microphone(void)
{
    i2s_chan_config_t chan_cfg = I2S_CHANNEL_DEFAULT_CONFIG(I2S_NUM_AUTO, I2S_ROLE_MASTER);
    ESP_ERROR_CHECK(i2s_new_channel(&chan_cfg, NULL, &rx_handle));

    i2s_pdm_rx_config_t pdm_rx_cfg = {
        .clk_cfg = I2S_PDM_RX_CLK_DEFAULT_CONFIG(CONFIG_EXAMPLE_SAMPLE_RATE),
        /* The default mono slot is the left slot (whose 'select pin' of the PDM microphone is pulled down) */
        .slot_cfg = I2S_PDM_RX_SLOT_DEFAULT_CONFIG(I2S_DATA_BIT_WIDTH_16BIT, I2S_SLOT_MODE_MONO),
        .gpio_cfg = {
            .clk = CONFIG_EXAMPLE_I2S_CLK_GPIO,
            .din = CONFIG_EXAMPLE_I2S_DATA_GPIO,
            .invert_flags = {
                .clk_inv = false,
            },
        },
    };
    ESP_ERROR_CHECK(i2s_channel_init_pdm_rx_mode(rx_handle, &pdm_rx_cfg));
    ESP_ERROR_CHECK(i2s_channel_enable(rx_handle));
}

void app_main(void)
{
    printf("PDM microphone recording example start\n--------------------------------------\n");
    // Mount the SDCard for recording the audio file
    mount_sdcard();
    // Acquire a I2S PDM channel for the PDM digital microphone
    init_microphone();
    ESP_LOGI(TAG, "Starting recording for %d seconds!", CONFIG_EXAMPLE_REC_TIME);
    // Start Recording
    record_wav(CONFIG_EXAMPLE_REC_TIME);
    // Stop I2S driver and destroy
    ESP_ERROR_CHECK(i2s_channel_disable(rx_handle));
    ESP_ERROR_CHECK(i2s_del_channel(rx_handle));
}

Flash the program to the XIAO ESP32S3:

idf.py build
idf.py flash

Finally, Get the recorded audio file from the SD card.

Download audio

1.3 Accelerometer

In my project, I have integrated a accelerometer. It is an LIS3DH sensor, which features an I2C interface and requires the following pins:

Mission Objectives

1. Establish I2C communication between XIAO ESP32S3 and ADXL345L
2. Capture I2C protocol waveforms using logic analyzer
3. Parse data from 0x32 start register to obtain 3-axis acceleration values

ADXL345L Technical Specifications

Core Parameters

Parameter	Specification
Communication Protocol	I2C/SPI (I2C used)
Measurement Range	±2g/±4g/±8g/±16g
Resolution (±2g)	4mg/LSB
Output Data Rate	0.1Hz - 3200Hz
Operating Voltage	2.0V - 3.6V
I2C Address	0x53 (SDO=GND)

Register Configuration
• 0x32: X-axis low byte (X0)
• 0x33: X-axis high byte (X1)
• 0x34: Y-axis low byte (Y0)
• 0x35: Y-axis high byte (Y1)
• 0x36: Z-axis low byte (Z0)
• 0x37: Z-axis high byte (Z1)

Hardware Connection Guide

1. XIAO ESP32S3 ↔ ADXL345L Wiring

ADXL345L Pin	XIAO ESP32S3 Pin
VCC	3.3V
GND	GND
SDA	D4 (I2C_SDA)
SCL	D5 (I2C_SCL)
SDO	GND (Address 0x53)

2. Logic Analyzer Connection

Analyzer Channel	Connection Point
CH0	SDA (White wire)
CH1	SCL (Red wire)
GND	Board GND

Connect ADXL345L to XIAO ESP32S3 with logic analyzer

Software Implementation

1. Arduino Code Framework

#include <Wire.h>
#include <ADXL345.h>

ADXL345 adxl; //variable adxl is an instance of the ADXL345 library

void setup() {
    Serial.begin(9600);
    adxl.powerOn();

    //set activity/ inactivity thresholds (0-255)
    adxl.setActivityThreshold(75); //62.5mg per increment
    adxl.setInactivityThreshold(75); //62.5mg per increment
    adxl.setTimeInactivity(10); // how many seconds of no activity is inactive?

    //look of activity movement on this axes - 1 == on; 0 == off
    adxl.setActivityX(1);
    adxl.setActivityY(1);
    adxl.setActivityZ(1);

    //look of inactivity movement on this axes - 1 == on; 0 == off
    adxl.setInactivityX(1);
    adxl.setInactivityY(1);
    adxl.setInactivityZ(1);

    //look of tap movement on this axes - 1 == on; 0 == off
    adxl.setTapDetectionOnX(0);
    adxl.setTapDetectionOnY(0);
    adxl.setTapDetectionOnZ(1);

    //set values for what is a tap, and what is a double tap (0-255)
    adxl.setTapThreshold(50); //62.5mg per increment
    adxl.setTapDuration(15); //625us per increment
    adxl.setDoubleTapLatency(80); //1.25ms per increment
    adxl.setDoubleTapWindow(200); //1.25ms per increment

    //set values for what is considered freefall (0-255)
    adxl.setFreeFallThreshold(7); //(5 - 9) recommended - 62.5mg per increment
    adxl.setFreeFallDuration(45); //(20 - 70) recommended - 5ms per increment

    //setting all interrupts to take place on int pin 1
    //I had issues with int pin 2, was unable to reset it
    adxl.setInterruptMapping(ADXL345_INT_SINGLE_TAP_BIT,   ADXL345_INT1_PIN);
    adxl.setInterruptMapping(ADXL345_INT_DOUBLE_TAP_BIT,   ADXL345_INT1_PIN);
    adxl.setInterruptMapping(ADXL345_INT_FREE_FALL_BIT,    ADXL345_INT1_PIN);
    adxl.setInterruptMapping(ADXL345_INT_ACTIVITY_BIT,     ADXL345_INT1_PIN);
    adxl.setInterruptMapping(ADXL345_INT_INACTIVITY_BIT,   ADXL345_INT1_PIN);

    //register interrupt actions - 1 == on; 0 == off
    adxl.setInterrupt(ADXL345_INT_SINGLE_TAP_BIT, 1);
    adxl.setInterrupt(ADXL345_INT_DOUBLE_TAP_BIT, 1);
    adxl.setInterrupt(ADXL345_INT_FREE_FALL_BIT,  1);
    adxl.setInterrupt(ADXL345_INT_ACTIVITY_BIT,   1);
    adxl.setInterrupt(ADXL345_INT_INACTIVITY_BIT, 1);
}

void loop() {

    //Boring accelerometer stuff
    int x, y, z;
    adxl.readXYZ(&x, &y, &z); //read the accelerometer values and store them in variables  x,y,z
    // Output x,y,z values
    Serial.print("values of X , Y , Z: ");
    Serial.print(x);
    Serial.print(" , ");
    Serial.print(y);
    Serial.print(" , ");
    Serial.println(z);

    double xyz[3];
    double ax, ay, az;
    adxl.getAcceleration(xyz);
    ax = xyz[0];
    ay = xyz[1];
    az = xyz[2];
    Serial.print("X=");
    Serial.print(ax);
    Serial.println(" g");
    Serial.print("Y=");
    Serial.print(ay);
    Serial.println(" g");
    Serial.print("Z=");
    Serial.print(az);
    Serial.println(" g");
    Serial.println("**********************");
    delay(500);

}

Logic Analyzer Verification

1. Typical I2C Communication Waveform

I2C protocol capture for axis data reading

Waveform Characteristics
• Start Condition: SDA falls while SCL high
• Address Frame: 0x53 (7-bit address + R/W bit)
• Register Write: 0x32 start address
• Data Read: 6-byte continuous read (ACK after each byte)

2. Data Parsing Validation

Register	Raw Value (HEX)	Calculation	Acceleration (g)
0x32 (X0)	0x34	52 × 0.00376390	+0.1957g
0x33 (X1)	0x00
0x34 (Y0)	0x05	-251 × 0.00376009	-0.9438g
0x35 (Y1)	0xFF
0x36 (Z0)	0x43	67 × 0.00349265	+0.2340g
0x37 (Z1)	0x00

1.4 Resources

tip

All project code is open-source and available at the following links:

• openGlasses Project Code
• Camera Example Code
• PCB