ESP-IDF Code

#include <stdio.h>
#include "freertos/FreeRTOS.h"
#include "driver/gpio.h"
#include "esp_log.h"
#include "driver/i2c_master.h"

// Settings
static const char* TAG = "AirQuality";

// I2C Variables
i2c_master_bus_handle_t bus_handle; // this will hold the bus
i2c_master_dev_handle_t scd40_handle;

void setup_i2c_bus() {
    i2c_master_bus_config_t i2c_mst_config = {
    .clk_source = I2C_CLK_SRC_DEFAULT,
    .i2c_port = I2C_NUM_1, // tried 0,-1 to no avail
    .scl_io_num = 4,
    .sda_io_num = 3,
    .glitch_ignore_cnt = 7,
    .flags.enable_internal_pullup = true,
    };

    ESP_ERROR_CHECK(i2c_new_master_bus(&i2c_mst_config, &bus_handle));
}

void setup_scd40_device() {
    i2c_device_config_t scd40_dev_cfg = {
        .dev_addr_length = I2C_ADDR_BIT_LEN_7,
        .device_address = 0x62,
        .scl_speed_hz = 100000,
    };

    ESP_ERROR_CHECK(i2c_master_bus_add_device(bus_handle, &scd40_dev_cfg, &scd40_handle));
}

void start_scd40() {
    uint8_t periodic_measurement_cmd[2] = {0x21, 0xb1};
    ESP_ERROR_CHECK(i2c_master_transmit(scd40_handle, periodic_measurement_cmd, sizeof(periodic_measurement_cmd), -1));
    vTaskDelay(pdMS_TO_TICKS(5000));
}

void read_scd40() {
    uint8_t read_measurement_cmd[2] = {0xec, 0x05};
    i2c_master_transmit(scd40_handle, read_measurement_cmd, sizeof(read_measurement_cmd), -1);
    vTaskDelay(pdMS_TO_TICKS(1));

    uint8_t buf[9];
    i2c_master_receive(scd40_handle, buf, sizeof(buf), -1);

    // TODO: buf[2] is the crc of CO2, which should be checked
    uint16_t co2 = (buf[0] << 8) | buf[1];
    // TODO: buf[5] is the crc of TEMP, which should be checked
    uint16_t temp_hex = (buf[3] << 8) | buf[4];
    float temperature = -45.0 + 175.0 * ((float)temp_hex / 65535.0);
    // TODO: buf[5] is the crc of HUM, which should be checked
    uint16_t hum_hex = (buf[6] << 8) | buf[7];
    float humidity = 100.0 * ((float)hum_hex / 65535.0);

    ESP_LOGI("SCD40", "CO2: %u ppm | Temp: %.2f C | Hum: %.2f %%", co2, temperature, humidity);
}

void stop_scd40() {
    uint8_t stop_measurement_cmd[2] = {0x3f, 0x86};
    i2c_master_transmit(scd40_handle, stop_measurement_cmd, sizeof(stop_measurement_cmd), -1);
    vTaskDelay(pdMS_TO_TICKS(500));
    ESP_LOGI(TAG, "Stopped SCD40 periodic measurement");
}

void app_main(void)
{
    vTaskDelay(pdMS_TO_TICKS(5000));
    ESP_LOGI(TAG, "Starting...");

    setup_i2c_bus();
    setup_scd40_device();

    start_scd40();

    for (uint8_t i = 0; i < 30; i++) {
        read_scd40();
        vTaskDelay(pdMS_TO_TICKS(5000));
    }

    stop_scd40();
}