Raspberry Pi Pico: RCWL-0516 Microwave Radar Proximity Sensor (Arduino IDE)

In this guide, you’ll learn how to use the RCWL-0516 Microwave Radar Proximity sensor to detect motion with the Raspberry Pi Pico programmed using Arduino IDE. We’ll show you how to wire the sensor and write an Arduino sketch to detect when motion is detected. The RCWL-0516 is a great alternative to the popular PIR motion sensor.

New to the Raspberry Pi Pico? Read the following guide: Getting Started with Raspberry Pi Pico (and Pico W).

Table of Contents:

Throughout this tutorial, we’ll cover the following contents:

• Introducing the RCWL-0516 Microwave Radar Proximity Sensor
• RCWL-0516 Sensor Pinout
• Microwave Radar Proximity Sensor vs PIR Motion Sensor
• Wiring the RCWL-0516 Sensor to the Raspberry Pi Pico
• Raspberry Pi Pico with the RCWL-0516 Sensor – Arduino Sketch

We have a similar tutorial using Raspberry Pi Pico with MicroPython firmware: Raspberry Pi Pico: RCWL-0516 Microwave Radar Proximity Sensor (MicroPython).

Prerequisites

You need to install the Raspberry Pi Pico boards on Arduino IDE and you must know how to upload code to the board. Check out the following tutorial first if you haven’t already:

• Programming Raspberry Pi Pico with Arduino IDE

Introducing the RCWL-0516 Microwave Radar Proximity Sensor

The RCWL-0516 is a small, inexpensive sensor that uses microwave radar to detect the presence of moving objects. The sensor works by emitting a beam of microwaves and then detecting the Doppler shift in the reflected waves as objects move past.

Usually, these sensors are sold as a pack of five and don’t come with header pins. So, you may need to get header pins separately and then solder them yourself.

Where to Buy?

You can check the following link on Maker Advisor and compare the price in different stores.

• RCWL-0516 Microwave Radar Proximity Sensor

You can use the preceding links or go directly to MakerAdvisor.com/tools to find all the parts for your projects at the best price!

How does it work?

The RCWL-0516 sensor has a built-in oscillator that generates a microwave signal at a frequency of 3.18 GHz. The sensor then sends out this signal in a 360-degree pattern.

When an object moves within the sensor’s range, the reflected waves are picked up by the sensor’s receiver. The receiver then measures the frequency of the reflected waves and compares it to the frequency of the original signal. If the frequency of the reflected waves has changed, the sensor knows that an object has moved.

The RCWL-0516 sensor has a single output pin that goes HIGH when it detects movement. It outputs LOW when no motion is detected.

RCWL-0516 Sensor Features

The RCWL-0516 has a detection range of up to 7 meters and can detect objects moving at speeds of up to 2 meters per second. It also has a built-in adjustable delay time, which can be used to prevent the sensor from triggering repeatedly on the same object.

Here’s a summary of some of the key features of the RCWL-0516 sensor:

• Uses microwave radar to detect moving objects
• Detection range of up to 7 meters
• Can detect objects moving at speeds of up to 2 meters per second
• Built-in adjustable delay time
• Low power consumption
• Inexpensive

RCWL-0516 sensor specifications:

• Supply voltage: 4–28 VDC
• Operating frequency: 3.18 GHz
• Sensing distance: 5–7 m
• Output level: 3.4V High <0.7 Low
• Output drive: 100mA
• Output timing: 2 second retrigger with motion

You can get more information about the sensor on the following GitHub page:

• RCWL-0516 Github page

Optional Light Depend Resistor (LDR) Sensor

The sensor comes with the option to solder a light-depend resistor (light sensor) if you want your sensor to operate just in dark conditions, for example. You can get the output of the LDR sensor on the LDR pin. Alternatively, you can also connect the LDR to the CDS pin.

When the output of the LDR is bigger than 0.7V, the OUT pin will output a HIGH signal when motion is detected. If motion is detected but the output of the LDR is smaller than 0.7V, the output will be LOW. This means that when attaching an LDR, the sensor will only sense motion when it’s dark.

You can adjust the sensitivity of the LDR, by connecting a resistor on the R-CDS pads (see the following section), or by adding a pull-up resistor externally in parallel with the CDS pin.

In my case, I added a pull-up 22KOhm resistor to the LDR pin so that it could detect motion when there is low light. Without the resistor, not even in very dark conditions I had a positive output. You might need to try different resistance values to see which one works best for your scenario.

Adjustment components

At the back of the sensor, there are three pads for additional SMD components (0805 dimensions):

The following information was taken from this GitHub page.

• C-TM: Regulate the repeat trigger time. The default (unpopulated) time is 2s. An SMD capacitor to extend the repeat trigger time. Pin 3 of the IC emits a frequency (f), and the trigger time in seconds is given by (1/f) * 32678.
• R-GN: The default detection range is 7m, adding a 1M resistor reduces it to 5m.
• R-CDS: Resistor in parallel with the 1M pullup. Without R-CDS, the lowest resistance of the LDR (i.e. highest light level) where the output is enabled is ~269kΩ (=0.7V). Adding resistance here decreases the LDR resistance of the enable/disable threshold. If the LDR resistance at the desired light level threshold is <269k then you could add an external resistor in series with the LDR.

RCWL-0516 Microwave Radar Proximity Sensor Pinout

The RCWL-0516 microwave radar proximity sensor has five pins:

• 3V3: this is the output from the voltage regulator (not the power pin)
• VIN: this is the power input pin. The sensor can be powered by a voltage range of 4-28V.
• GND: this is the ground pin.
• OUT: this is the output pin. The output pin goes HIGH when the sensor detects movement and remains LOW when it doesn’t.
• CDS: This pin is used to connect a light-dependent resistor (LDR). The LDR can be used to disable the sensor in bright light conditions.

The following table shows the pinout of the RCWL-0516 microwave radar proximity sensor:

3V3	3.3V power output (not to power the sensor)
GND	ground pin
OUT	output pin (goes HIGH when motion is detected)
VIN	input voltage to power the sensor (4V to 28V)
CDS	Light-dependent resistor output

Microwave Radar Proximity Sensor vs PIR Motion Sensor

The microwave radar proximity sensor is many times used as an alternative to the PIR motion sensor, depending on the project application. The following table compares both sensors:

	RCWL-0516 Microwave Radar	PIR Motion Sensor
How it works?	Active Sensor (emits microwave signals and detects reflections).	Passive Sensor (detects infrared radiation emitted by objects).
Detection Range	Longer range, typically up to 7+ meters.	Shorter range, typically a few meters, depending on the model.
Sensing Through Obstacles	Can sense through non-metallic materials.	Obstructed by certain materials (e.g., glass)
Sensitivity to Motion	Highly sensitive, may give false positives.	Not so sensitive, may miss subtle movements. Only detects living things that emit heat.
Coverage Area	Broad coverage with wide radar pattern.	Narrow field of view.

Connecting the RCWL-0516 Microwave Radar Proximity Sensor to the Raspberry Pi Pico

Follow the next table or schematic diagram to wire the RCWL-0516 microwave radar proximity sensor to the Raspberry Pi Pico:

RCWL-0516 Sensor	Raspberry Pi Pico
3V3	don’t connect
GND	GND
OUT	GPIO22 (or any other GPIO of your choice)
VIN	VBUS (or preferably an external power supply between 4V to 28V)
CDS	don’t connect

We’ll also connect an LED to GPIO 21 to give us a visual output when motion is detected. You can connect the LED to any other digital pin.

Parts Required:

• Raspberry Pi Pico
• RCWL-0516 Microwave Radar Sensor
• LED
• 220Ohm resistor
• Breadboard
• Jumper wires

We’re using the VBUS pin to power the RCWL-0516 sensor, but for better results, we recommend using an external power source (4V to 28V).

Raspberry Pi Pico with the RCWL-0516 Sensor – Arduino Sketch

Copy the following code to your Arduino IDE. This example is very straightforward. It simply reads the output of the sensor and prints in the Serial Monitor when motion is detected and lights up an LED accordingly (the LED is on when motion is detected).

/*********
  Rui Santos
  Complete project details at https://RandomNerdTutorials.com/raspberry-pi-pico-rcwl-0516-arduino/
  
  Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files.
  The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
*********/

int led = 21;                // the pin that the LED is attached to
int sensor = 22;              // the pin that the sensor is attached to
int state = LOW;             // by default, no motion detected
int val = 0;                 // variable to store the sensor status (value)

void setup() {
  pinMode(led, OUTPUT);      // initalize LED as an output
  pinMode(sensor, INPUT);    // initialize sensor as an input
  Serial.begin(115200);        // initialize serial
}

void loop(){
  val = digitalRead(sensor);   // read sensor value
  if (val == HIGH) {           // check if the sensor is HIGH
    digitalWrite(led, HIGH);   // turn LED ON
    
    if (state == LOW) {
      Serial.println("Motion detected!"); 
      state = HIGH;       // update variable state to HIGH
    }
  } 
  else {
      digitalWrite(led, LOW); // turn LED OFF
      
      if (state == HIGH){
        Serial.println("Motion stopped!");
        state = LOW;       // update variable state to LOW
    }
  }
}

View raw code

How the code works

Start by defining the pins for the LED and for the output pin of the sensor. We’re connecting an LED to GPIO 21, but you can use any other GPIO.

int led = 21;                // the pin that the LED is attached to

We’re connecting the output of the sensor to GPIO 22, but you can use any other pin.

int sensor = 15;              // the pin that the sensor is attached to

Then, initialize some variables. The state variable stores the current state of the output pin of the sensor and it is initially set to LOW.

int state = LOW;             // by default, no motion detected

The val variable will store the status (value) of the sensor’s digital output, either HIGH or LOW.

int val = 0;                 // variable to store the sensor status (value)

Basically, val is used to temporarily store the real-time output value of the sensor, while state is used to keep track of whether motion has been detected or not over time.

In the setup(), set the LED as an output and the sensor as an input. Also initialize the Serial Monitor at a baud rate of 115200.

void setup() {
  pinMode(led, OUTPUT);      // initalize LED as an output
  pinMode(sensor, INPUT);    // initialize sensor as an input
  Serial.begin(115200);        // initialize serial
}

In the loop(), we start by reading the sensor’s digital output (HIGH or LOW) and store it in the val variable.

val = digitalRead(sensor);   // read sensor value

If the sensor’s output is HIGH (motion detected), the LED turns on.

if (val == HIGH) {           // check if the sensor is HIGH
  digitalWrite(led, HIGH);   // turn LED ON

Then, we check if the previous status was LOW. If so, it means the state has changed and that motion have been detected. We print a message in the Serial Monitor and change the state variable to HIGH.

if (state == LOW) {
  Serial.println("Motion detected!"); 
  state = HIGH;       // update variable state to HIGH
}

If the sensor’s output is LOW (no motion detected), we turn the LED off.

else {
  digitalWrite(led, LOW); // turn LED OFF

If the previous state was HIGH and, if now the state is LOW, it means motion has stopped, and we can set the state variable to LOW.

if (state == HIGH){
  Serial.println("Motion stopped!");
  state = LOW;       // update variable state to LOW
}

Uploading the Code to the Raspberry Pi Pico

To upload code to the Raspberry Pi Pico, it needs to be in bootloader mode.

If the Raspberry Pi is currently running MicroPython firmware, you need to manually put it into bootloader mode. For that, connect the Raspberry Pi Pico to your computer while holding the BOOTSEL button at the same time.

For future uploads using Arduino IDE, the board should go automatically into bootloader mode without the need to press the BOOTSEL button.

Now, select your COM port in Tools > Port. It may be the case that the COM port is grayed out. If that’s the case, don’t worry it will automatically find the port once you hit the upload button.

Upload the code.

You should get a success message.

Demonstration

After uploading, open the Serial Monitor.

When motion is detected. You should get a “Motion detected” message followed by a “Motion stopped” message after two seconds.

Additionally, the LED will light up when motion is detected.

If you have an LDR connected, you’ll need to decrease the luminosity for the sensor to detect motion.

Wrapping Up

In this tutorial, you learned how to use the RCWL-0516 microwave radar proximity sensor with the Raspberry Pi Pico to detect motion in your surroundings. The RCWL-0516 might be a good alternative to the PIR motion sensor depending on your project requirements.

Want to learn more about the Raspberry Pi Pico? Check out the following tutorials:

• Raspberry Pi Pico: Read Analog Inputs (Arduino IDE)
• Raspberry Pi Pico: Fading an LED using PWM (Arduino IDE)
• Raspberry Pi Pico: DHT11/DHT22 Temperature and Humidity Sensor (Arduino IDE)

Check out all our Raspberry Pi Pico Guides »

If you prefer to program the Raspberry Pi Pico using MicroPython, you can get started with the following tutorial:

• Programming Raspberry Pi Pico with MicroPython

Thanks for reading.