🛠 Serveur web embarqué pour piloter une LED

Objectives

Host an HTTP server directly on the ESP32-S2 using the WebServer library: serve a control page, drive an LED via GET requests, and display the status. The S2 does not have Bluetooth: 2.4 GHz WiFi is the only network channel, which makes this server even more central.

Hardware

• ESP32-S2 board
• 1 LED + 330 Ω resistor on GPIO2
• 2.4 GHz WiFi network (no 5 GHz)
• Computer/smartphone on the same network

Complete code

// Serveur web de pilotage LED sur ESP32-S2
#include <WiFi.h>
#include <WebServer.h>

const char *SSID = "VOTRE_WIFI";
const char *PASS = "VOTRE_MOT_DE_PASSE";
const uint8_t LED_PIN = 2;
bool etatLed = false;
WebServer serveur(80);

const char *PAGE =
  "<!doctype html><html lang='fr'><head><meta charset='utf-8'>"
  "<meta name='viewport' content='width=device-width,initial-scale=1'>"
  "<title>ESP32-S2</title></head><body style='font-family:sans-serif;"
  "text-align:center;padding-top:40px'>"
  "<h1>LED ESP32-S2</h1><p>Etat : %s</p>"
  "<a href='/on'><button style='font-size:1.4em;padding:10px 24px'>ALLUMER</button></a> "
  "<a href='/off'><button style='font-size:1.4em;padding:10px 24px'>ETEINDRE</button></a>"
  "</body></html>";

void pageAccueil {
  String html; html.reserve(600);
  html.printf(PAGE, etatLed ? "ALLUMEE" : "ETEINTE");
  serveur.send(200, "text/html", html);
}

void setup {
  pinMode(LED_PIN, OUTPUT);
  Serial.begin(115200);
  WiFi.begin(SSID, PASS);
  Serial.print("Connexion WiFi");
  while (WiFi.status != WL_CONNECTED) { delay(300); Serial.print("."); }
  Serial.printf("\nAdresse : http://%s\n", WiFi.localIP.toString.c_str);
  serveur.on("/", pageAccueil);
  serveur.on("/on", []  { etatLed = true;  digitalWrite(LED_PIN, HIGH); serveur.send(303, "text/plain", "ok"); pageAccueil; });
  serveur.on("/off", [] { etatLed = false; digitalWrite(LED_PIN, LOW);  serveur.send(303, "text/plain", "ok"); pageAccueil; });
  serveur.begin;
}

void loop { serveur.handleClient; }

Expected verification

The console displays the IP assigned by the router (e.g., http://192.168.1.42). From a browser on the same network, the page displays with the current status; the TURN ON button lights the physical LED and updates the page, TURN OFF extinguishes it. Control works from multiple devices simultaneously.

Common errors

• 5 GHz network: The S2's radio is 2.4 GHz only, connection fails in a loop on a 5 GHz SSID.
• Forgetting serveur.handleClient in loop: the page never responds or freezes the browser.
• Using an ADC2 pin for a sensor in the same project: ADC2 is blocked as soon as WiFi is active; stick to ADC1 (GPIO1-14).
• Blocking in loop (long delays): the server stops responding; keep the loop lightweight or use delay(1) to yield control.