← Web Server OTA Firmware Updates on an ESP32 PLC

Web Server OTA Firmware Updates on an ESP32 PLC — full example

Embedded web server with OTA firmware updates on an ESP32 PLC: status page, JSON endpoint and browser .bin upload — no USB cable on the factory floor.

Complete, runnable program for the ESP32 PLC (webserver-ota-firmware.ino): wiring header, requirements and integration notes included.

Read-only preview.

/*
 * COMPLETE EXAMPLE — Embedded web server with OTA firmware update
 *
 * Hardware: ESP32 PLC (Industrial Shields, any model with WiFi)
 * Based on: textile monitoring project, modul_WebServer_v2.h
 *
 * Network:
 *   The PLCs are spread across the plant, next to each knitting machine:
 *   reflashing over USB means climbing a ladder. With OTA the update is
 *   done from the browser: http:///
 *
 * Endpoints:
 *   GET  /        HTML status page with a firmware upload form
 *   GET  /status  JSON with digital inputs, uptime and free heap
 *   POST /update  Receives the compiled .bin, flashes it and reboots
 *
 * Works together with other catalog examples:
 *   - nonblocking-wifi-reconnection.ino (the server only responds with network)
 *   - rtc-ntp-synchronization.ino (timestamp in /status)
 *   - mqtt-remote-commands.ino (complementary diagnostics without a browser)
 */

#include 
#include 
#include 

const char *WIFI_SSID = "WIFI_SSID";
const char *WIFI_PASS = "WIFI_PASS";
const int   PLC_ID    = 1;

WebServer server(80);

const int pins[] = {I0_0, I0_1, I0_2, I0_3, I0_4, I0_5};
const int NPINS = 6;

// ------------------------------------------------- Pages
void handleRoot() {
  String html =
    ""
    "
ESP32 PLC " + String(PLC_ID) + " — Textile monitoring
"
    "
Uptime: " + String(millis() / 1000) + " s | "
    "Free heap: " + String(ESP.getFreeHeap()) + " bytes
"
    "
/status (JSON)
"
    "
Update firmware (OTA)
"
    "
"
    " "
    "
"
    "";
  server.send(200, "text/html", html);
}

void handleStatus() {
  String json = "{\"id\":" + String(PLC_ID) +
                ",\"uptime_s\":" + String(millis() / 1000) +
                ",\"heap\":" + String(ESP.getFreeHeap()) + ",\"inputs\":{";
  for (int i = 0; i < NPINS; i++)
    json += "\"I0_" + String(i) + "\":" + String(digitalRead(pins[i])) +
            (i < NPINS - 1 ? "," : "");
  json += "}}";
  server.send(200, "application/json", json);
}

// ------------------------------------------------- OTA over HTTP POST
// First callback: final response + reboot. Second: chunks of the .bin
void setupOTA() {
  server.on("/update", HTTP_POST, []() {
      server.sendHeader("Connection", "close");
      server.send(200, "text/plain", Update.hasError() ? "FAIL" : "OK - rebooting");
      delay(1000);
      ESP.restart();                          // boots with the new firmware
    }, []() {
      HTTPUpload &up = server.upload();
      if (up.status == UPLOAD_FILE_START) {
        Serial.println("OTA: receiving " + up.filename);
        if (!Update.begin(UPDATE_SIZE_UNKNOWN)) Update.printError(Serial);
      } else if (up.status == UPLOAD_FILE_WRITE) {
        if (Update.write(up.buf, up.currentSize) != up.currentSize)
          Update.printError(Serial);
      } else if (up.status == UPLOAD_FILE_END) {
        if (Update.end(true))
          Serial.println("OTA OK: " + String(up.totalSize) + " bytes");
        else
          Update.printError(Serial);
      }
    });
}

void setup() {
  Serial.begin(115200);
  for (int i = 0; i < NPINS; i++) pinMode(pins[i], INPUT);

  WiFi.mode(WIFI_STA);
  WiFi.begin(WIFI_SSID, WIFI_PASS);
  uint32_t t0 = millis();
  while (WiFi.status() != WL_CONNECTED && millis() - t0 < 15000) delay(500);
  Serial.println("IP: " + WiFi.localIP().toString());

  server.on("/", HTTP_GET, handleRoot);
  server.on("/status", HTTP_GET, handleStatus);
  setupOTA();
  server.begin();
  Serial.println("OTA web server ready on port 80");
}

void loop() {
  server.handleClient();     // serve web requests

  // ... the normal PLC work continues here (pulses, MQTT, SD):
  // the web server only adds a few microseconds per loop iteration

  delay(5);
}