Radar hallway sensor on an ESP32-C3

// Home Assistant radar sensor: a hallway light that waits for the dark.
//
//   RCWL-0516 on GPIO 18   microwave Doppler radar, OUT high while it sees movement
//   light module on GPIO 0 the analog output of an LDR board, darker reads higher
//   LED on GPIO 19         the hallway light, standing in for a relay or a smart bulb
//
// Honest first: the RCWL-0516 is not an mmWave presence sensor. It is a 3.2 GHz
// Doppler board that sees MOVEMENT, like a PIR that also sees through plastic
// and thin walls. Sit perfectly still and it lets go. The 24 GHz mmWave boards
// people use for true presence, such as the LD2410, also sense the tiny motion
// of breathing and talk over UART; Mokxi does not model them. What this sketch
// shows is the trick everybody uses with a motion sensor anyway: an off delay,
// so a short pause does not turn the lights out (ESPHome calls it delayed_off).
//
// The light logic runs on the device, so the hallway still works when Home
// Assistant is down. Mokxi has no MQTT broker: the sketch prints what it would
// publish, and serves its state as JSON at /state for the Web tab.

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

const int RADAR_PIN = 18;
const int LIGHT_SENSOR_PIN = 0;
const int LAMP_PIN = 19;

const unsigned long OFF_DELAY_MS = 10000;  // keep "occupied" this long after the last movement
const int DARK_ABOVE = 3000;               // raw reading, 0 to 4095: higher is darker

WebServer server(80);

bool moving = false;
bool occupied = false;
bool lampOn = false;
bool lastDark = false;
unsigned long lastMovement = 0;

void publish(const char *topic, const char *payload) {
  Serial.print("publish home/hallway/");
  Serial.print(topic);
  Serial.print(' ');
  Serial.println(payload);
}

bool isDark() {
  // A little hysteresis, so dusk does not flicker the light on and off.
  int raw = analogRead(LIGHT_SENSOR_PIN);
  if (lastDark) lastDark = raw > DARK_ABOVE - 150;
  else lastDark = raw > DARK_ABOVE;
  return lastDark;
}

void setLamp(bool on) {
  if (on == lampOn) return;
  lampOn = on;
  digitalWrite(LAMP_PIN, on ? HIGH : LOW);
  publish("light", on ? "ON" : "OFF");
}

void sendState() {
  String json = "{\"motion\":";
  json += moving ? "true" : "false";
  json += ",\"occupancy\":";
  json += occupied ? "true" : "false";
  json += ",\"light\":";
  json += lampOn ? "true" : "false";
  json += ",\"light_level\":";
  json += String(analogRead(LIGHT_SENSOR_PIN));
  json += "}";
  server.send(200, "application/json", json);
}

void setup() {
  Serial.begin(115200);
  pinMode(RADAR_PIN, INPUT);
  pinMode(LAMP_PIN, OUTPUT);
  digitalWrite(LAMP_PIN, LOW);

  Serial.println("Radar hallway sensor: simulated WiFi, no MQTT broker in Mokxi.");
  WiFi.begin("Mokxi-Lab", "breadboard");
  while (WiFi.status() != WL_CONNECTED) {
    delay(250);
  }
  Serial.print("online at http://");
  Serial.print(WiFi.localIP());
  Serial.println("/state");
  server.on("/state", sendState);
  server.on("/", sendState);
  server.begin();
  publish("occupancy", "OFF");
}

void loop() {
  server.handleClient();
  unsigned long now = millis();

  bool seen = digitalRead(RADAR_PIN) == HIGH;
  if (seen != moving) {
    moving = seen;
    publish("motion", moving ? "ON" : "OFF");
  }
  if (moving) lastMovement = now;

  // Occupied the moment anything moves, clear only after a quiet OFF_DELAY_MS.
  if (moving && !occupied) {
    occupied = true;
    publish("occupancy", "ON");
  } else if (!moving && occupied && now - lastMovement >= OFF_DELAY_MS) {
    occupied = false;
    publish("occupancy", "OFF");
    setLamp(false);
  }
  // While someone is about, the light comes on as soon as it is dark enough.
  if (occupied && !lampOn && isDark()) setLamp(true);
  delay(10);
}