ESP32 WiFi Servo Pulse Controller

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

WebServer server(80);
const char* AP_PASSWORD = "CHANGE_ME_1234"; // Replace with your own 8-63 character password.
bool httpReady = false;

void redirectHome() {
  server.sendHeader("Location", "/");
  server.send(303, "text/plain", "Open the control page\n");
}
String pageStart(const char* title) {
  String page = "<!doctype html><html lang='en'><head>";
  page += "<meta name='viewport' content='width=device-width,initial-scale=1'>";
  page += "<style>body{font:1.1rem system-ui;max-width:40rem;margin:2rem auto;padding:1rem}button,input{font:inherit;margin:.5rem 0}input[type=range]{width:100%}</style>";
  page += "<title>"; page += title; page += "</title></head><body><h1>";
  page += title; page += "</h1>";
  return page;
}
void sendPage(const String& page) {
  server.sendHeader("Cache-Control", "no-store");
  server.send(200, "text/html; charset=utf-8", page + "</body></html>");
}
bool parseUnsigned(const String& text, uint16_t minimum, uint16_t maximum, uint16_t& value) {
  if (text.length() == 0 || text.length() > 4) return false;
  uint32_t n = 0;
  for (size_t i = 0; i < text.length(); ++i) {
    char c = text[i];
    if (c < '0' || c > '9') return false;
    n = n * 10 + (c - '0');
  }
  if (n < minimum || n > maximum) return false;
  value = uint16_t(n); return true;
}
void startHTTP(const char* name) {
  server.onNotFound([]() { server.send(404, "text/plain", "No such route\n"); });
  if (!WiFi.mode(WIFI_AP) || !WiFi.softAP(name, AP_PASSWORD, 6, false, 1)) {
    Serial.println("AP failed; output stays off. Check board and password length.");
    return;
  }
  server.begin(); httpReady = true;
  Serial.print("Join "); Serial.println(name);
  Serial.print("Open http://"); Serial.println(WiFi.softAPIP());
}

constexpr uint8_t SIGNAL_PIN = 25, RESOLUTION = 16;
constexpr uint16_t MIN_US = 1400, CENTER_US = 1500, MAX_US = 1600;
constexpr uint32_t FRAME_US = 20000, COMMAND_LIFETIME_MS = 15000;
bool enabled = false;
uint16_t lastPulseUs = CENTER_US;
uint32_t lastCommand = 0;

uint32_t pulseTicks(uint16_t us) {
  return (uint32_t(us) * (1UL << RESOLUTION) + FRAME_US / 2) / FRAME_US;
}
void disablePulses() {
  if (enabled) {
    bool zeroOK = ledcWrite(SIGNAL_PIN, 0);
    bool detached = ledcDetach(SIGNAL_PIN);
    if (!zeroOK || !detached) Serial.println("LEDC stop reported an error; remove external power");
  }
  enabled = false;
  pinMode(SIGNAL_PIN, OUTPUT); digitalWrite(SIGNAL_PIN, LOW);
  Serial.println("Pulse output disabled; servo supply is NOT switched off");
}
bool writePulse(uint16_t us) {
  if (!enabled || !ledcWrite(SIGNAL_PIN, pulseTicks(us))) { disablePulses(); return false; }
  lastPulseUs = us; lastCommand = millis(); return true;
}
void showPage() {
  String page = pageStart("ESP32 bounded servo control");
  page += String("<p>Pulse output: ") + (enabled ? "enabled" : "disabled") + ".</p>";
  page += "<p>Last accepted pulse: " + String(lastPulseUs) + " us; this is not measured position.</p>";
  page += "<form method='post' action='/arm'><button>Enable at 1500 us</button></form>";
  page += "<form method='post' action='/pulse'><label for='pulse'>Pulse width 1400 to 1600 us</label>";
  page += "<input id='pulse' name='us' type='range' min='1400' max='1600' step='10' value='";
  page += String(lastPulseUs) + "'><button>Apply pulse</button></form>";
  page += "<form method='post' action='/off'><button>Disable pulse output</button></form>";
  page += "<p>Enable can cause immediate movement. Commands expire after 15 seconds; disabling pulses is NOT a certified stop or power isolation.</p>";
  sendPage(page);
}
void setup() {
  Serial.begin(115200);
  pinMode(SIGNAL_PIN, OUTPUT); digitalWrite(SIGNAL_PIN, LOW);
  server.on("/", HTTP_GET, showPage);
  server.on("/arm", HTTP_POST, []() {
    if (server.args() != 0) { server.send(400, "text/plain", "No arguments expected\n"); return; }
    if (!enabled) enabled = ledcAttach(SIGNAL_PIN, 50, RESOLUTION);
    if (!enabled || !writePulse(CENTER_US)) {
      disablePulses(); server.send(503, "text/plain", "Pulse driver unavailable\n"); return;
    }
    Serial.println("Pulse output enabled at 1500 us; keep clear of movement");
    redirectHome();
  });
  server.on("/pulse", HTTP_POST, []() {
    uint16_t next = 0;
    if (server.args() != 1 || !server.hasArg("us") ||
        !parseUnsigned(server.arg("us"), MIN_US, MAX_US, next)) {
      server.send(400, "text/plain", "Exactly one integer us, 1400 through 1600, is required\n"); return;
    }
    if (!enabled) { server.send(409, "text/plain", "Enable at center before moving\n"); return; }
    if (!writePulse(next)) { server.send(503, "text/plain", "Pulse write failed\n"); return; }
    Serial.printf("Accepted pulse %u us; no position feedback\n", unsigned(next));
    redirectHome();
  });
  server.on("/off", HTTP_POST, []() {
    if (server.args() != 0) { server.send(400, "text/plain", "No arguments expected\n"); return; }
    disablePulses(); redirectHome();
  });
  startHTTP("ESP32-WebServo");
}
void loop() {
  if (httpReady) server.handleClient();
  if (enabled && millis() - lastCommand >= COMMAND_LIFETIME_MS) {
    Serial.println("Command expired"); disablePulses();
  }
  delay(1);
}