ESP32 DS18B20 Web Dashboard

#include <Arduino.h>
#include <WiFi.h>
#include <WebServer.h>
#include <OneWire.h>

constexpr uint8_t DATA_PIN = 4;
const char* AP_NAME = "ESP32-Temperature";
const char* AP_PASSWORD = "CHANGE_ME_1234"; // Replace before use, 8-63 characters.
OneWire bus(DATA_PIN);
WebServer server(80);
uint8_t address[8];
bool sensorReady = false, converting = false, valid = false, serverReady = false;
uint32_t started = 0, lastAttempt = 0, lastGood = 0;
float temperature = 0;

bool configureSensor() {
  uint8_t extra[8];
  bus.reset_search();
  if (!bus.search(address) || address[0] != 0x28 ||
      OneWire::crc8(address, 7) != address[7]) return false;
  if (bus.search(extra)) return false; // This example deliberately supports ONE device.
  if (!bus.reset()) return false;
  bus.select(address); bus.write(0xB4); // Read Power Supply.
  if (!bus.read_bit()) return false;   // Parasite power is not supported here.
  if (!bus.reset()) return false;
  bus.select(address); bus.write(0x4E); // Write volatile scratchpad, not EEPROM.
  bus.write(0); bus.write(0); bus.write(0x7F); // TH, TL, 12-bit configuration.
  return true;
}
bool readResult() {
  uint8_t scratch[9];
  if (!bus.reset()) return false;
  bus.select(address); bus.write(0xBE);
  for (uint8_t &b : scratch) b = bus.read();
  if (OneWire::crc8(scratch, 8) != scratch[8] || scratch[4] != 0x7F ||
      scratch[7] != 0x10) return false;
  int16_t raw = int16_t((uint16_t(scratch[1]) << 8) | scratch[0]);
  float c = raw / 16.0f;
  if (c < -55 || c > 125) return false;
  temperature = c;
  return true;
}
void sampleTask() {
  uint32_t now = millis();
  if (!sensorReady) return;
  if (converting && now - started >= 800) {
    converting = false;
    valid = readResult();
    if (valid) {
      lastGood = millis();
      Serial.printf("Temperature %.2f C\n", temperature);
    } else Serial.println("Sensor read failed; dashboard marks reading unavailable");
  }
  if (!converting && now - lastAttempt >= 2000) {
    lastAttempt = now;
    if (!bus.reset()) { valid = false; return; }
    bus.select(address); bus.write(0x44, 0); // Externally powered conversion.
    started = millis(); converting = true;
  }
}
void setup() {
  Serial.begin(115200);
  sensorReady = configureSensor();
  Serial.println(sensorReady ? "One externally powered DS18B20 found" :
    "Need exactly one family-0x28 externally powered sensor; fix wiring and reset");
  lastAttempt = millis() - 2000;
  if (!WiFi.mode(WIFI_AP) || !WiFi.softAP(AP_NAME, AP_PASSWORD)) {
    Serial.println("AP failed; check password length and board"); return;
  }
  server.on("/", HTTP_GET, []() {
    String page = "<!doctype html><html lang='en'><meta name='viewport' content='width=device-width,initial-scale=1'>";
    page += "<meta http-equiv='refresh' content='3'><title>Local temperature</title><h1>DS18B20 temperature</h1>";
    if (valid && millis() - lastGood < 5000) {
      page += "<p>" + String(temperature, 2) + " &deg;C</p><p>Sample age: ";
      page += String(millis() - lastGood) + " ms</p>";
    } else page += "<p>Reading unavailable. Check Serial and sensor wiring.</p>";
    page += "<p>Refreshes every 3 seconds. Local read-only demonstration.</p></html>";
    server.sendHeader("Cache-Control", "no-store");
    server.send(200, "text/html; charset=utf-8", page);
  });
  server.onNotFound([]() { server.send(404, "text/plain", "Not found\n"); });
  server.begin(); serverReady = true;
  Serial.print("Join "); Serial.println(AP_NAME);
  Serial.print("Open http://"); Serial.println(WiFi.softAPIP());
}
void loop() {
  if (serverReady) server.handleClient();
  sampleTask();
  delay(1);
}