Working Principle
The RCWL-0516 is a microwave Doppler radar motion detector that transmits a continuous 3.18 GHz signal and detects frequency shifts in the reflected signal caused by moving objects. When a person or object moves, the reflected microwave frequency shifts proportionally to the object’s radial velocity (Doppler effect). The on-board ASIC processes this shift and outputs a digital HIGH/LOW signal.
Key advantage over PIR (HC-SR501): Microwave radar penetrates thin walls, plastic enclosures, and glass — it can detect motion through a closed project box. PIR requires a direct line-of-sight to warm objects.
Electrical Characteristics
| Parameter | Value |
|---|---|
| Operating Frequency | 3.181 GHz (ISM band) |
| Detection Range | 5–7 m (default) |
| Supply Voltage | 4–28 V DC |
| Current Draw | ~2.8 mA (active), <3 µA (idle) |
| Output | Digital: HIGH (3.3 V) on motion, LOW (0 V) idle |
| Hold Time | ~2 sec (adjustable via CDS pad resistor) |
| Trigger Repeat | Repeatable (re-triggers on continued motion) |
| Detection Angle | ~360° (omnidirectional through enclosure) |
| Board Size | ~17.3 × 35.9 mm |
Interfacing with an MCU
Dead simple: 3 pins — VIN (5 V), GND, OUT. The OUT pin goes HIGH (3.3 V) when motion is detected. Connect directly to a 3.3 V or 5 V MCU digital input. No pull-up resistors needed.
Calibration
- Range: Add a resistor to the R-GN pad to reduce detection range; remove the default 1 MΩ jumper for maximum range
- Hold time: Modify the capacitor on C-TM pad — larger value = longer hold time after trigger
- Light sensitivity: The CDS pad accepts an LDR to disable detection in bright conditions (daylight inhibit)
Code Example
/*
* RCWL-0516 Microwave Motion Sensor — Arduino
* Wiring: VIN → 5V, GND → GND, OUT → Pin 3
* Output: HIGH (3.3V) on motion, LOW on idle
*/
#define RADAR_PIN 3
void setup() {
Serial.begin(9600);
pinMode(RADAR_PIN, INPUT);
Serial.println("RCWL-0516 Microwave Radar Ready");
delay(3000); /* Allow initial settling */
}
void loop() {
if (digitalRead(RADAR_PIN) == HIGH) {
Serial.println("Motion detected! (microwave)");
} else {
Serial.println("No motion");
}
delay(200);
}Real-World Applications
Through-Wall Detection & Concealed Automation
Because microwave radar detects through plastic, wood, and drywall, RCWL-0516 is ideal for concealed motion-activated lighting, automatic faucets behind countertops, alarm systems inside sealed enclosures, and occupancy sensing behind wall panels. It complements PIR sensors in dual-technology detectors that require both RF and thermal motion for reduced false alarms.
Limitations
- Motion only: Detects movement, not presence — a stationary person will not trigger the sensor.
- False triggers: Fans, swaying curtains, or vibrating machinery can cause false detections.
- No direction: Cannot determine the direction or distance of the moving object.
- RF interference: Other 3 GHz devices or strong EMI can cause false triggers.
- Omnidirectional: Detects through walls in all directions, which may be undesirable in some installations.