Wi-Fi Connection

[中文]

Let’s now get this power outlet on a Wi-Fi network. In this Chapter we will connect to a hard-coded Wi-Fi network that is embedded within the device’s firmware executable image. You may refer to the 3_wifi_connection/ directory of esp-jumpstart for looking at this code.

The Code

#include <esp_wifi.h>
#include <esp_event_loop.h>

tcpip_adapter_init();
esp_event_loop_init(event_handler, NULL);

wifi_init_config_t cfg = WIFI_INIT_CONFIG_DEFAULT();
esp_wifi_init(&cfg);
esp_wifi_set_mode(WIFI_MODE_STA);

wifi_config_t wifi_config = {
    .sta = {
        .ssid = EXAMPLE_ESP_WIFI_SSID,
        .password = EXAMPLE_ESP_WIFI_PASS,
    },
 };
esp_wifi_set_config(ESP_IF_WIFI_STA, &wifi_config);
esp_wifi_start();

In the above code:

• We initialize the TCP/IP stack with the tcpip_adapter_init() call
• Similarly, the Wi-Fi subsystem and its station interface is initialized with the calls to esp_wifi_init() and esp_wifi_set_mode()
• Finally, the hard-coded SSID and passphrase configuration of the target Wi-Fi network are configured and we start the station using a call to esp_wifi_start()

Wi-Fi is a protocol that can generate asynchronous events like connectivity lost, connection established, DHCP Address received etc. The event loop collects events from the TCP/IP Stack and the Wi-Fi subsystem. The call to esp_event_loop_init() initialises the event loop. The event loop delivers these events to the callback that is registered through the first parameter.

The asynchronous event handler that is registered with the event loop can be implemented as:

esp_err_t event_handler(void *ctx, system_event_t *event)
{
    switch(event->event_id) {
    case SYSTEM_EVENT_STA_START:
        esp_wifi_connect();
        break;
    case SYSTEM_EVENT_STA_GOT_IP:
        ESP_LOGI(TAG, "Connected with IP Address:%s",
             ip4addr_ntoa(&event->event_info.got_ip.ip_info.ip));
        break;
    case SYSTEM_EVENT_STA_DISCONNECTED:
        esp_wifi_connect();
        break;
    return ESP_OK;
}

The event handler current handles 3 events. When it receives an event SYSTEM_EVENT_STA_START, it asks the station interface to connect using the esp_wifi_connect() call. The same action is taken even when we receive a Wi-Fi disconnect event.

The event SYSTEM_EVENT_STA_GOT_IP is received when a DHCP IP address is obtained by ESP32. In this particular case, we only print the IP address on the console.

Progress so far

You can now modify the application to enter your Wi-Fi network’s SSID and the passphrase. When you compile and flash this code on your development board, the ESP32 should connect to your Wi-Fi network and print the IP address on the console. The outlet’s functionality of toggling the GPIO on pressing the push-button is, of course, also retained.

One problem with this approach is that the Wi-Fi settings are hard-coded into the firmware image. While this is ok for a hobby project, a product will require the end-user to dynamically configure this device with their settings. This is what we will look at in the next chapter.