📋 Overview
The RCWL-0516 Microwave Doppler Radar Sensor Module is a motion detector that uses microwave radar instead of infrared to detect movement. Unlike PIR sensors (such as the HC-SR501) that only detect warm-bodied objects like people and animals, the RCWL-0516 detects motion from any moving object — people, animals, and even non-living things — by measuring changes in reflected microwave signals.
The module transmits a continuous low-power microwave signal at approximately 3.18 GHz. When an object moves within its detection range, the frequency of the reflected signal shifts slightly (the Doppler effect). The onboard RCWL-9196 IC detects this frequency shift and outputs a HIGH signal (3.3V) on the OUT pin for approximately 2–3 seconds before returning to LOW (0V).
Because microwaves can pass through walls, glass, thin wood, and plastic enclosures, this sensor can be mounted inside a project box or behind a panel and still detect motion — something a PIR sensor cannot do.
⭐ Key Features
- Microwave Doppler radar detection — detects motion from any moving object, not just warm bodies
- ~7 meter (21 ft) detection range — adjustable via onboard resistor pad
- 360° detection pattern — detects through the board from both sides (front side is more sensitive)
- Penetrates obstacles — works through walls, glass, thin wood, and plastic enclosures
- Simple digital output — OUT pin goes HIGH (3.3V) when motion is detected, LOW (0V) when idle
- ~2–3 second trigger hold time — adjustable by adding a capacitor to the C-TM pad
- Repeat trigger behavior — output stays HIGH as long as motion continues
- Light-sensing input (CDS pad) — optional LDR connection to disable detection in bright light (daylight inhibit)
- Wide operating voltage — 4V to 28V input with onboard 3.3V regulator
- Ultra-compact size — approximately 17.3mm × 35.9mm
- Low current consumption — approximately 2.8mA at 5V
📡 How Doppler Radar Detection Works
The RCWL-0516 uses a principle called the Doppler effect to detect motion. Here's how it works in simple terms:
- The module transmits microwaves — The onboard antenna continuously broadcasts a low-power microwave signal at approximately 3.18 GHz
- Signals bounce off objects — These microwaves reflect off objects in the surrounding area and return to the sensor
- Moving objects shift the frequency — When an object is moving, the reflected signal comes back at a slightly different frequency than what was transmitted (this is the Doppler effect — the same reason an ambulance siren sounds higher-pitched as it approaches and lower-pitched as it drives away)
- The IC detects the shift — The RCWL-9196 chip compares the transmitted and reflected frequencies. If it detects a frequency shift (meaning something moved), it sets the OUT pin HIGH
- Output goes HIGH for ~2–3 seconds — The OUT pin stays at 3.3V for approximately 2–3 seconds, then returns to 0V. If motion continues, the output remains HIGH (repeat trigger)
📝 Note: Because microwaves pass through non-metallic materials, this sensor can detect motion through walls, doors, glass, and plastic enclosures. However, it cannot penetrate metal — metal surfaces will block or reflect the signal.
📌 Module Pinout
The RCWL-0516 has 5 pins along one edge of the board. Looking at the component side (the side with the IC and capacitors) with the pins at the bottom:
| Pin | Label | Function |
|---|---|---|
| 1 | 3V3 | 3.3V regulated output (can power small external circuits, ~100mA max) |
| 2 | GND | Ground |
| 3 | OUT | Digital output — HIGH (3.3V) when motion detected, LOW (0V) when idle |
| 4 | VIN | Power supply input (4V – 28V DC) |
| 5 | CDS | Light sensor input — connect an LDR here to disable detection in bright light (optional) |
⚠️ Important: The OUT pin outputs 3.3V, not 5V. This is safe for both 3.3V and 5V Arduino boards (5V Arduinos read 3.3V as HIGH). However, if you're driving a relay or other 5V logic device directly from OUT, you may need a level shifter or transistor.
🔧 Onboard Configuration Pads
The RCWL-0516 has several solder pads on the board that allow you to customize its behavior. These are not populated by default — you solder your own components onto them.
C-TM — Trigger Hold Time (Repeat Trigger Duration)
By default, the OUT pin stays HIGH for approximately 2 seconds after motion is detected. You can increase this time by soldering a capacitor across the C-TM pads.
| Capacitor Value | Approximate Hold Time |
|---|---|
| None (default) | ~2 seconds |
| 0.2µF | ~2 seconds |
| 0.47µF | ~5 seconds |
| 1µF | ~8 seconds |
| 2.2µF | ~15 seconds |
| 4.7µF | ~30 seconds |
| 10µF | ~60 seconds |
💡 Tip: Use a ceramic or film capacitor for best results. If using an electrolytic capacitor, observe correct polarity.
R-GN — Detection Range (Sensitivity)
The default detection range is approximately 7 meters (~21 feet). You can reduce the detection range by soldering a resistor across the R-GN pads. A 1MΩ resistor reduces the range to approximately 1–2 meters. Smaller resistor values reduce the range further.
📝 Note: You can only reduce the range from the default 7m — there is no way to increase it beyond 7m.
CDS — Light Dependent Resistor (LDR) for Daylight Inhibit
The RCWL-0516 has a built-in daylight inhibit feature that lets you disable motion detection when ambient light is bright — perfect for outdoor security lights that should only activate at night.
This feature works by controlling Pin 9 of the RCWL-9196 IC (the output enable pin). Pin 9 is pulled HIGH by an onboard 1MΩ resistor, which keeps the sensor enabled by default. When an LDR pulls Pin 9 below ~0.7V (in bright light), the sensor output is disabled.
Two Ways to Connect the LDR
The module provides two physical connection points for the LDR — both are electrically identical (they connect to the same Pin 9 on the IC). Use whichever is more convenient for your project:
| Connection Point | Location on Board | Best For |
|---|---|---|
| CDS Solder Pad | Two plated-through holes in the corner of the board (opposite the pin header) | Compact builds — solder the LDR directly onto the board |
| CDS Pin (Pin 5) | Last pin in the header row | Remote mounting — connect the LDR via jumper wires so it can be positioned away from the sensor (e.g., poking through an enclosure) |
⚠️ Important: Use one or the other, not both at the same time. Connecting LDRs to both the pad and the pin simultaneously will put two components in parallel on the same circuit node and produce unpredictable behavior.
How to Wire the LDR
- Option A (CDS Pad): Solder an LDR (e.g., GL5528) directly into the two plated-through holes on the board. No additional wiring needed.
- Option B (CDS Pin): Connect one leg of the LDR to the CDS pin (Pin 5) and the other leg to GND.
No external pull-up resistor is needed — the module has an internal 1MΩ pull-up on Pin 9.
How It Works
- In darkness: LDR resistance is very high (hundreds of kΩ) → Pin 9 stays HIGH → sensor operates normally
- In bright light: LDR resistance drops below ~269kΩ → Pin 9 is pulled below 0.7V → sensor output is disabled
R-CDS Pad — Adjusting the Light Threshold
The R-CDS pad (a separate solder pad on the board) allows you to fine-tune the light level at which the sensor disables. Soldering a resistor here adds resistance in parallel with the onboard 1MΩ pull-up, which lowers the effective pull-up resistance. This makes it easier for the LDR to pull Pin 9 low, meaning the sensor will disable at lower light levels (i.e., it becomes more sensitive to light).
💡 Tip: Most projects work fine without an R-CDS resistor. Only add one if you need to fine-tune the exact light level at which the sensor turns off. A standard 5mm LDR (GL5528 or similar) works well with the default 1MΩ pull-up.
📏 Mechanical Drawing/Dimensions
🏗️ Schematic / Circuit Diagram
🔌 Wiring the RCWL-0516 to Arduino
📦 Parts Needed
- 1× RCWL-0516 Microwave Radar Sensor Module (this product)
- 1× Arduino Uno, Nano, or compatible board
- 1× LED and 220Ω resistor (optional, for visual indicator)
- Jumper wires
Basic Wiring (3 Wires)
| RCWL-0516 Pin | Arduino Pin |
|---|---|
| VIN | 5V |
| GND | GND |
| OUT | Pin 2 (or any digital pin) |
Optional: Adding an LED Indicator
To add a visual indicator that lights up when motion is detected:
- Connect a 220Ω resistor from Arduino Pin 13 to the anode (long leg) of an LED
- Connect the cathode (short leg) of the LED to GND
Optional: Adding an LDR for Daylight Inhibit
To disable detection in bright light, see the section "CDS — Light Dependent Resistor (LDR) for Daylight Inhibit" above.
📝 Note: The 3V3 pin on the RCWL-0516 is a regulated 3.3V output from the module's onboard regulator. You can use it to power small external circuits (up to ~100mA), but do not connect it to the Arduino's 5V pin.
🚀 Step 1: Basic Motion Detection Sketch
This simple sketch reads the RCWL-0516 output and prints "Motion Detected!" to the Serial Monitor. It also lights the built-in LED on Pin 13.
/*
* RCWL-0516 Basic Motion Detection
* Envistia Mall - Product Support
*
* Connections:
* RCWL-0516 VIN -> Arduino 5V
* RCWL-0516 GND -> Arduino GND
* RCWL-0516 OUT -> Arduino Pin 2
*/
const int sensorPin = 2;
const int ledPin = 13;
void setup() {
Serial.begin(9600);
pinMode(sensorPin, INPUT);
pinMode(ledPin, OUTPUT);
Serial.println("RCWL-0516 Motion Sensor Ready");
Serial.println("Waiting for motion...");
delay(3000); // Allow sensor to stabilize
}
void loop() {
int motionDetected = digitalRead(sensorPin);
if (motionDetected == HIGH) {
digitalWrite(ledPin, HIGH);
Serial.println("Motion Detected!");
} else {
digitalWrite(ledPin, LOW);
Serial.println("No Motion");
}
delay(500);
}
How to Use:
- Upload the sketch to your Arduino
- Open the Serial Monitor at 9600 baud
- Wait 3 seconds for the sensor to stabilize
- Walk in front of the sensor — you should see "Motion Detected!" in the Serial Monitor and the LED on Pin 13 will light up
- Stand still — after ~2 seconds the output returns to "No Motion"
🚀 Step 2: Motion Detection with Cooldown Timer
This improved sketch adds a cooldown period to prevent rapid re-triggering, and provides cleaner Serial Monitor output by only printing when the state changes:
/*
* RCWL-0516 Motion Detection with Cooldown
* Envistia Mall - Product Support
*
* Prints state changes only (not every loop).
* Includes a cooldown timer to prevent rapid re-triggering.
*
* Connections:
* RCWL-0516 VIN -> Arduino 5V
* RCWL-0516 GND -> Arduino GND
* RCWL-0516 OUT -> Arduino Pin 2
*/
const int sensorPin = 2;
const int ledPin = 13;
bool lastState = LOW;
unsigned long lastTriggerTime = 0;
const unsigned long cooldownMs = 5000; // 5-second cooldown
void setup() {
Serial.begin(9600);
pinMode(sensorPin, INPUT);
pinMode(ledPin, OUTPUT);
Serial.println("RCWL-0516 Motion Sensor Ready");
delay(3000); // Allow sensor to stabilize
}
void loop() {
int currentState = digitalRead(sensorPin);
if (currentState == HIGH && lastState == LOW) {
unsigned long now = millis();
if (now - lastTriggerTime > cooldownMs) {
digitalWrite(ledPin, HIGH);
Serial.print("Motion Detected at ");
Serial.print(now / 1000);
Serial.println(" seconds");
lastTriggerTime = now;
}
}
if (currentState == LOW && lastState == HIGH) {
digitalWrite(ledPin, LOW);
Serial.println("Motion Ended - Sensor Ready");
}
lastState = currentState;
delay(100);
}
🚀 Step 3 (Optional): Motion-Activated Relay
This sketch activates a relay when motion is detected — useful for turning on lights, fans, or other devices automatically. The relay stays on for a configurable duration after the last detected motion.
📦 Additional Parts Needed
- 1× Relay module (5V, active-HIGH or active-LOW)
- 1× NPN transistor (2N2222 or similar) — if driving a bare relay coil
- 1× 1kΩ resistor — base resistor for transistor
- 1× 1N4007 diode — flyback protection for relay coil
💡 Tip: If you're using a pre-built relay module (the kind with a screw terminal block and indicator LED), it typically has the transistor and flyback diode built in. Just connect the signal pin directly to an Arduino digital pin.
Additional Wiring
| Component | Arduino Pin |
|---|---|
| Relay Module Signal (IN) | Pin 7 |
| Relay Module VCC | 5V |
| Relay Module GND | GND |
Motion-Activated Relay Code
/*
* RCWL-0516 Motion-Activated Relay
* Envistia Mall - Product Support
*
* Turns on a relay when motion is detected.
* Relay stays on for a configurable duration after
* the last motion event.
*
* Connections:
* RCWL-0516 VIN -> Arduino 5V
* RCWL-0516 GND -> Arduino GND
* RCWL-0516 OUT -> Arduino Pin 2
* Relay Signal -> Arduino Pin 7
*/
const int sensorPin = 2;
const int relayPin = 7;
const int ledPin = 13;
unsigned long lastMotionTime = 0;
const unsigned long relayOnDuration = 30000; // 30 seconds
bool relayState = false;
void setup() {
Serial.begin(9600);
pinMode(sensorPin, INPUT);
pinMode(relayPin, OUTPUT);
pinMode(ledPin, OUTPUT);
digitalWrite(relayPin, LOW);
Serial.println("Motion-Activated Relay Ready");
delay(3000);
}
void loop() {
int motionDetected = digitalRead(sensorPin);
if (motionDetected == HIGH) {
lastMotionTime = millis();
if (!relayState) {
digitalWrite(relayPin, HIGH);
digitalWrite(ledPin, HIGH);
relayState = true;
Serial.println("Motion! Relay ON");
}
}
// Turn off relay after duration with no motion
if (relayState && (millis() - lastMotionTime > relayOnDuration)) {
digitalWrite(relayPin, LOW);
digitalWrite(ledPin, LOW);
relayState = false;
Serial.println("Timeout - Relay OFF");
}
delay(100);
}
⚖️ RCWL-0516 vs. HC-SR501 PIR Sensor
Both the RCWL-0516 and the HC-SR501 are popular motion detection modules, but they work very differently. Here's a comparison to help you choose the right one for your project:
| Feature | RCWL-0516 (Microwave Radar) | HC-SR501 (PIR Infrared) |
|---|---|---|
| Detection Method | Microwave Doppler radar (3.18 GHz) | Passive infrared (heat signature) |
| Detects | Any moving object (people, animals, objects) | Warm-bodied objects only (people, animals) |
| Detection Range | ~7m (adjustable down) | ~7m (adjustable) |
| Detection Angle | ~360° (through board, both sides) | ~120° cone (front only) |
| Through-Wall Detection | Yes — works through glass, wood, plastic, drywall | No — requires direct line of sight |
| Affected by Temperature | No | Yes — less reliable in hot environments |
| False Triggers | More likely (detects fans, curtains, vibrations) | Less likely (only detects heat changes) |
| Trigger Hold Time | ~2s default (adjustable via C-TM pad) | ~3s–300s (adjustable via potentiometer) |
| Sensitivity Adjustment | Solder resistor on R-GN pad | Onboard potentiometer (easy to adjust) |
| Daylight Inhibit | Yes — via LDR on CDS pad | No (requires external circuit) |
| Operating Voltage | 4V – 28V | 4.5V – 20V |
| Output Voltage | 3.3V HIGH | 3.3V HIGH |
| Size | ~17mm × 36mm (very small) | ~32mm × 24mm + Fresnel lens dome |
| Best For | Hidden/enclosed mounting, through-wall detection, hot environments | General-purpose motion detection, fewer false triggers |
💡 Tip: For the most reliable motion detection system, consider using both sensors together — require both to trigger before activating your output. This dramatically reduces false alarms while maintaining good detection coverage.
🎯 Common Applications
- Motion-activated lighting — Automatic lights that turn on when someone enters a room
- Security and alarm systems — Intrusion detection for homes and offices
- Occupancy detection — Detect whether a room is occupied for HVAC or energy management
- Automatic doors and gates — Trigger door openers when someone approaches
- Hidden sensor installations — Mount behind walls, inside enclosures, or under countertops
- Smart home automation — Trigger IoT events using ESP32/ESP8266
- Interactive displays and exhibits — Activate displays when visitors approach
- Robotics — Obstacle and proximity detection for mobile robots
🛠️ Troubleshooting
| Problem | Possible Cause | Solution |
|---|---|---|
| No output / always LOW | Incorrect wiring | Verify VIN→5V, GND→GND, OUT→digital pin. Check that you're reading the correct pin in your code. |
| Output is always HIGH | Metal objects too close to antenna | Remove any metal objects within 1cm of the board. Move the sensor away from metal surfaces, enclosures, or large wires. |
| Constant false triggers | Detecting unintended motion (fans, curtains, vibrations, WiFi interference) | Reduce sensitivity by soldering a 1MΩ resistor on the R-GN pad. Move the sensor away from fans, HVAC vents, and vibrating surfaces. Keep away from WiFi routers. |
| Detecting through walls (unwanted) | Normal behavior — microwaves penetrate walls | Reduce range with R-GN resistor. Shield the back of the board with a grounded metal plate or copper tape to limit detection to one direction. |
| Sensor triggers immediately on power-up | Normal startup behavior | Add a 3-second delay in your setup() function to allow the sensor to stabilize before reading the output. |
| Very short detection range | Metal near antenna or low supply voltage | Ensure no metal is within 1cm of the antenna area. Verify VIN is receiving at least 4V. Check that the component side faces the detection area. |
| Sensor doesn't detect stationary people | Normal behavior — Doppler radar only detects motion | This sensor detects movement, not presence. A stationary person will not be detected. Consider using a PIR sensor or combining both sensors for better coverage. |
| LDR (daylight inhibit) not working | LDR not connected correctly | Connect LDR between the CDS pin and GND. Verify the LDR changes resistance with light (test with a multimeter). No additional resistor is needed. |
💡 Tips for Best Results
- Component side faces the detection area — The component side of the board (with the IC and capacitors) is the primary detection side. It will also detect from the back, but at lower sensitivity.
- Keep metal away from the antenna — Do not place any metal objects within 1cm of the board, especially near the antenna trace. Metal interferes with the microwave signal and causes false triggers or reduced range.
- Allow 3 seconds for startup — The sensor needs a few seconds to stabilize after power-up. Always include a delay in your setup() before reading the output.
- Shield the back for directional detection — If you only want to detect motion in one direction, place a grounded metal plate or copper tape behind the board to block rear detection.
- Reduce sensitivity for indoor use — The default 7m range may be too much for small rooms. Solder a 1MΩ resistor on the R-GN pad to reduce range to 1–2 meters.
- Use the CDS pin for outdoor projects — Connect an LDR to the CDS pin to automatically disable detection during daylight hours (great for security lights).
- Avoid mounting near WiFi routers — The 3.18 GHz operating frequency is close to the 2.4 GHz WiFi band. Strong WiFi signals can occasionally cause interference.
- Combine with a PIR sensor for reliability — Use both an RCWL-0516 and an HC-SR501 together, requiring both to trigger, to virtually eliminate false alarms.
⚠️ Important Notes
- The OUT pin outputs 3.3V (not 5V) when triggered. This is sufficient for Arduino digital inputs but may not directly drive 5V relay modules without a transistor or level shifter.
- This sensor detects motion only — it cannot detect a stationary person or object. If someone stops moving, the output will return to LOW after the hold time expires.
- Microwaves pass through most non-metallic materials. The sensor will detect motion through walls, floors, and ceilings. Plan your mounting location accordingly to avoid unwanted triggers.
- The onboard configuration pads (C-TM, R-GN, R-CDS) require soldering. There are no potentiometers or jumpers for adjustment.
- The 3V3 pin is a regulated output, not a power input. Do not apply external voltage to this pin.
- Operating frequency is approximately 3.18 GHz. Check local regulations if using in commercial or industrial applications.
🛒 Where to Buy the RCWL-0516
Buy the RCWL-0516 Microwave Doppler Radar Sensor Module →
📚 Resources & Downloads
- RCWL-0516 Datasheet (PDF): RCWL-0516 Datasheet — MakerHero
- Tutorial Reference 1: Interfacing RCWL-0516 with Arduino (Last Minute Engineers)
- Tutorial Reference 2: Arduino with RCWL-0516 Microwave Radar Sensor (Random Nerd Tutorials)
- Tutorial Reference 3: All About RCWL-0516 Microwave Radar Motion Sensor (Instructables)
- RCWL-0516 Information on GitHub: https://github.com/jdesbonnet/RCWL-0516
-
Video: RCWL0516 Module Review and Test by JohnAudioTech on Youtube:
This guide is provided by Envistia Mall for educational and technical reference purposes. The manufacturer and Envistia LLC (dba Envistia Mall) are not responsible for any damages or losses resulting from the use of this product. Always follow proper electrical safety practices when working with electronic components. Specifications are based on manufacturer data and are subject to change without notice.