RCWL-0516 microwave motion sensor

The RCWL-0516 Doppler radar module: OUT goes high when something moves in range, even through plastic and thin walls.

Aliases: RCWL-0516, microwave radar sensor, Doppler motion sensor. It does what the HC-SR501 PIR does by another method: a 3.2 GHz oscillator sends out a signal, and anything moving shifts the echo's frequency by a few hertz, which the RCWL-9196 chip on the board turns into a pulse.

Pins

Pin	What it does
3V3	The board's own 3.3 V regulator output, up to 100 mA.
GND	Ground.
OUT	High, at 3.3 V, while movement is seen and for the hold time after.
VIN	Supply, 4 to 28 V.
CDS	The light sensor pads. Pulled below about 0.7 V, the sensor is off. Leave it open.

Reading it on an Arduino

No library: digitalRead(pin) on OUT. 3.3 V is well over a 5 V board's input threshold.

void setup() {
  pinMode(2, INPUT);
  pinMode(13, OUTPUT);
}

void loop() {
  digitalWrite(13, digitalRead(2));
}

While it runs

Click the board to start something moving in range and click again to stop it. The dot above OUT shows the pin.

What the model gets right

OUT rises at once to the board's 3.3 V, continued movement keeps it high, and it drops hold seconds after the movement stops (2 s with the stock board). Unlike a PIR there is no dead time after a pulse and no single-shot jumper. CDS pulled low turns the sensor off, and 3V3 is a 3.3 V source while VIN is powered.

What it does not model

The range (about 7 m) and what is in the way: something is either moving in range or it is not. False triggers from fans, vibration or a second sensor nearby.

Common mistakes

Mounting it behind metal: the radar does not see through it. Expecting it to ignore the next room: it sees through walls, which is often not what you want.

See it in action

Radar light lights the Uno's LED from it. Open it at /templates.