Light, distance and motion

LD2410 radar with ESP32

A PIR sensor sees movement, so it switches off the lights on someone reading a book. The LD2410 is a millimetre-wave radar that also picks up a person sitting still, which is why it has become popular for room presence. On a wall panel it can also wake the screen when someone walks up.

It has two ways to connect. The easy one is the OUT pin: high when someone is there, low when not. That is one wire and one digitalRead, which is what the example does. The UART gives more, with distances and gate settings, but it runs at 256000 baud, so use hardware serial pins and cross TX and RX. Forum threads on this sensor mostly come down to three things: crossed lines, wrong baud rate and weak power. Some users had to feed it from a separate 5 V supply, not the board's 5V pin.

Do not mix up the names. An LD2420 is a different board, and one user needed 115200 baud on it. A fan, a curtain moving in warm air, or a pet can all count as presence, so expect some tuning, and radar passes through thin walls and plastic, so it may see the next room. ESPHome exposes the gate settings. Its example uses 6 m as a maximum distance, but check the manual for your version. Keep it away from the display's power section and mount it where it faces the room. On many display boards the spare UART is already in use. LCD Ultra Pro can read a hardware pin, so the OUT signal can drive a rule without code.

const int OUT_PIN = 5;
int last = -1;

void setup() {
  Serial.begin(115200);
  pinMode(OUT_PIN, INPUT);
}

void loop() {
  int now = digitalRead(OUT_PIN);
  if (now != last) {
    last = now;
    Serial.println(now ? "Someone is here" : "Room is empty");
  }
  delay(100);
}

Use this information at your own risk. It is for general guidance only: the example code compiles, but it has not been tested on every part, and modules differ between sellers. Check the manufacturer's data before you build. Product names belong to their owners, and LCD Ultra Pro is not affiliated with them. See our Terms.