RCWL-0516 Microwave Radar Motion Sensor

RCWL 0516 practical reference

A microwave Doppler sensor that detects motion through glass and thin plastic, often used where PIR sensors are blocked by enclosures.

Key specifications

• Sensor type: RF microwave Doppler radar, operating at 3.18 GHz (unlicensed ISM band)
• Detection range: ~5-9 meters, depending on target size and PCB antenna orientation
• Operating voltage: 4V–28V DC input, with an onboard regulator providing a 3.3V rail (~100 mA available) for external use
• Output: 3.3V digital HIGH on the OUT pin while motion is detected
• Output hold time: ~2 seconds by default after last detected motion, adjustable by modifying the onboard Cds/R-GN solder pads
• Penetration: Passes through non-metallic materials — glass, thin plastic, drywall — unlike PIR sensors, which these materials block
• Power draw: Continuously transmitting RF — not a low-power sensor; no sleep state like PIR modules have
• Interface: Digital output (OUT) — simple HIGH/LOW read, no bus protocol

Pinout and connection notes

This sensor never sleeps — unlike PIR, it's continuously emitting and listening for RF reflections, so it draws power the whole time it's on. Avoid it for battery-only, low-power designs; PIR is dramatically more efficient for that use case.

Keep metal away from the antenna trace — the sensing element is a PCB trace acting as an antenna. Nearby metal enclosures, wires bundled too close, or even a metal screw near the board can detune it, causing false triggers, reduced range, or a sensor that never stops reporting motion. Give it several cm of clearance from metal on all sides where possible.

Hold time is fixed on stock boards — the ~2 second output-hold behavior after motion stops is set by an onboard resistor/capacitor pair (labeled R-GN / Cds pads on most boards). Changing it requires a physical component swap, not a software setting.

CDS pin is optional — if you want the sensor to only report motion in darkness (e.g., a nightlight trigger), wire a photoresistor to the CDS pad per the module's silkscreen; most projects leave this pin unconnected and it works fine at full sensitivity regardless of ambient light.

• VIN: Power input, 4-28V DC
• GND: Ground
• 3V3: Onboard 3.3V regulator output — usable to power other low-current logic, not just an input
• OUT: Motion detection output, 3.3V HIGH while triggered
• CDS: Light-sensitivity gate input — pairs with an external photoresistor to disable detection above a chosen light level (often left unconnected)

Integration checklist

1. Confirm the exact part number and breakout-board revision.
2. Verify supply voltage, current demand, logic levels, and signal direction against the datasheet.
3. Check controller pin assignments and bus address or interface mode against the example code.
4. Power up with external loads disconnected, then test signals before full integration.
5. If readings or communication fail, check power and ground first, then pin mapping, interface settings, and library initialization.

Troubleshooting and reproducibility

Record the board used, wiring, library/version, supply arrangement, and measured behavior. Use the selected board-specific wiring example as the source of truth. Never assume visually similar modules share identical voltage tolerance or pin order.