WiFi and NTP

WiFi provides two things: automatic time synchronisation via NTP, and a web interface for configuring alarms and uploading audio files.

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WiFi Station Mode

#include "esp_wifi.h"
#include "esp_event.h"

void wifi_init_sta(const char *ssid, const char *password) {
    esp_netif_init();
    esp_event_loop_create_default();
    esp_netif_create_default_wifi_sta();

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

    wifi_config_t sta_cfg = {};
    strncpy((char *)sta_cfg.sta.ssid,     ssid,     32);
    strncpy((char *)sta_cfg.sta.password, password, 64);

    esp_wifi_set_mode(WIFI_MODE_STA);
    esp_wifi_set_config(WIFI_IF_STA, &sta_cfg);
    esp_wifi_start();
    esp_wifi_connect();
}

Register event handlers to react to connection and disconnection:

esp_event_handler_register(WIFI_EVENT, WIFI_EVENT_STA_DISCONNECTED,
                            wifi_reconnect_handler, NULL);
esp_event_handler_register(IP_EVENT,   IP_EVENT_STA_GOT_IP,
                            wifi_connected_handler, NULL);

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Storing Credentials in NVS

Never hardcode WiFi credentials in source code. Store them in NVS:

// Save (once, from provisioning)
nvs_handle_t h;
nvs_open("wifi", NVS_READWRITE, &h);
nvs_set_str(h, "ssid",     "MyNetwork");
nvs_set_str(h, "password", "MyPassword");
nvs_commit(h);
nvs_close(h);

// Load at boot
nvs_open("wifi", NVS_READONLY, &h);
nvs_get_str(h, "ssid",     ssid,     &ssid_len);
nvs_get_str(h, "password", password, &pass_len);
nvs_close(h);

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SoftAP Provisioning

If NVS has no credentials (first boot), start the ESP32 as a WiFi access point and run a minimal HTTP server for credential entry:

static void provisioning_start(void) {
    wifi_config_t ap_cfg = {
        .ap = {
            .ssid            = "AlarmClock-Setup",
            .ssid_len        = 0,
            .password        = "configure",
            .max_connection  = 1,
            .authmode        = WIFI_AUTH_WPA2_PSK,
        }
    };
    esp_wifi_set_mode(WIFI_MODE_AP);
    esp_wifi_set_config(WIFI_IF_AP, &ap_cfg);
    esp_wifi_start();

    // Start HTTP server on 192.168.4.1
    // User connects to AlarmClock-Setup, opens browser to 192.168.4.1
    // POSTs SSID and password, ESP32 saves to NVS and reboots
}

Alternatively, use the built-in wifi_provisioning component from ESP-IDF, which handles the SoftAP + provisioning protocol for you.

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NTP Sync

Start NTP sync after WiFi connects:

static void wifi_connected_handler(void *arg, esp_event_base_t base,
                                   int32_t id, void *data) {
    ntp_init();  // starts SNTP, fires ntp_sync_callback when complete
}

The clock remains functional if WiFi is unavailable. The RTC keeps accurate time independently. NTP sync is a "make it more accurate" enhancement.

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Web Interface (Alarm Configuration)

The ESP32 HTTP server (esp_http_server) lets you configure alarms from a browser:

Endpoint	Method	Action
/	GET	Clock status page
/alarms	GET	List configured alarms (JSON)
/alarms	POST	Add or update an alarm
/alarms/{id}	DELETE	Remove an alarm
/upload	POST	Upload a WAV file to /lfs/alarms/ (OTA audio update)
/timezone	POST	Set timezone string

Implementing the full web interface is beyond the scope of this guide, but the ESP-IDF HTTP server example is a good starting point.