Here the Python equivalent code for Raspberry Pi

import os
import sys
import getpass
import time
import pigpio
import RPi.GPIO as GPIO

# #include <VirtualWire.h>

env=os.path.expanduser(os.path.expandvars('/home/' + getpass.getuser() + '/lib'))
sys.path.insert(0, env)

import piVirtualWire.piVirtualWire as piVirtualWire

PIN_RADAR = 4 # #define PIN_RADAR 2
PIN_TX = 17 # #define PIN_TX 9
# PIN_LED = 13 # #define PIN_LED 13 # print instead

# void setup()
baud_rate = 1000 # baud rate instead of bps connection speed

GPIO.setmode(GPIO.BCM)
GPIO.setup(PIN_RADAR, GPIO.IN)
# GPIO.setup(PIN_LED, GPIO.OUT)

# not needed
# pinMode(PIN_LED, OUTPUT);

pi = pigpio.pi()

# vw_set_tx_pin(PIN_TX); # and
# vw_setup(6000);
tx = piVirtualWire.tx(pi, PIN_TX, baud_rate)

rv = -1 # int rv = -1; # "unused"

try:
# void loop()
while True:
#print("PIN_LED would be HIGH if you want to use it")
# GPIO.output(PIN_LED, GPIO.HIGH) # LED on # digitalWrite(PIN_LED, HIGH);
v = GPIO.input(PIN_RADAR) # int v = digitalRead(PIN_RADAR);

if(v != rv):
rv = v
# char msg[20];
# sprintf(msg, "R %lu %d", millis() / 1000, v);
msg = "R %f %d" % (time.time(), v)
tx.put(msg) # vw_send((uint8_t *)msg, strlen(msg));
print(msg) # Serial.println(msg);
tx.waitForReady() # vw_wait_tx();
#print("PIN_LED would be LOW if you want to use it")
# GPIO.output(PIN_LED, GPIO.LOW) # LED off # digitalWrite(PIN_LED, LOW);
time.sleep(0.1)

except KeyboardInterrupt: # press Ctrl + C to stop
GPIO.cleanup()
tx.cancel()
pi.stop()

OUT is digital logic high with motion. There is no point trying to use this with an analog input.

https://github.com/jdesbonnet/RCWL-0516

http://forum.hobbycomponents.com/viewtopic.php?f=73&t=2181

Throw away your Arduinos (not because it was then a great platform back in 2003) and stick any LED on OUT to GND. It is current limited (according to my tests) with the entire spectrum of LED, from Red to Blue, White and UV and none require a current limiting resistor. A single LED will show the status and then attach this OUT to a GPIO on a Raspberry Pi Zero W (wifi). Running node-RED I have my cat-detector logging time and date to a file, emailing and tweeting me at any motion.

My 80 yr neighbor was worried about people coming in her apartment upstairs, so I put a 'cat-detector' in a plastic box with a Pi0W powered by a USB power bank and left it (with her permission) just before she went away for a few days. I logged into the Pi with ssh and looked at the log file and gave her a printed report the moment I got emailed when she came home. Her departure data showed a final event and arrival a few days later with no other activity in between.

VIN is 4 to 28 volts, OUT is a logic 3.3 volt digital output on motion detection and GND of course. The confusing part is 3V3 which is a 100 mA voltage regulated output which can be used to power external devices only. 

https://github.com/jdesbonnet/RCWL-0516/issues/6

I put a load resistor on 3V3 for 100 mA and increased VIN from 5 to 16 volts and got stable regulated voltage out, but it got hot beyond specs at 16 v for a full load. Below 5 v it was not able to regulate at full load. Consider this a very inexpensive freebee but ignore 3V3 if you don't need to power anything else.

Also ignore the CDS (CaDmium-Sulfide) and added LDR photocell, input and just let it float, the intent is to inhibit the OUT signal at light/dark, who cares, it is a very stupid feature (or bug) and does not shut off the RF transmission as the thing draws 3.15 mA irregardless. (not a word :D)

If you want to control the RF output then drive the sensor VIN from a transistor (4 volt minium, better 5) and allow at least 10 seconds for the device to stabilize on powerup.

The device is at the very lowest limits of S band microwaves (upper UHF) and is not radar as an object-detection system that uses radio waves to determine the range, angle, or velocity. All it does is detect reflections or interference between out and in and eventually turns on OUT by internal analog circuitry. It can not be used to detirmine distance, velocity or whatever but relative motion of an incoming cat or lion. Luxury!

http://forum.hobbycomponents.com/viewtopic.php?f=73&t=2181

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If you want the latest inexpensive systems then buy an STM8S103 MINDEV board, a TTL UART dongle for console I/O, a one-time USB Programmer, an RCWL-0516 and get the latest free eForth software from:

https://github.com/TG9541/stm8ef/wiki/

3V3 is not module power supply, it is 3.3 V OUTPUT. Module power supply is IN (4 - 28 V) and you get 3.3 V at OUT pin when the module detects motion. You can use 3V3 pin as power supply for something requiring 3.3 V.

Hey, just wanted to point out the similar efforts going on at: https://github.com/jdesbonnet/RCWL-0516

Maybe you could contact that maintainer and collaborate?

Sorry - I was changing a few items, this one works:

int sensorPin = 8; 
int ledPin = 3; 
int motion; // Variable to read detection of movement

void setup() {
  Serial.begin(9600); 
  pinMode (sensorPin, INPUT); 
  pinMode (ledPin, OUTPUT); 
}
void loop() {
  motion = digitalRead(sensorPin); // Read digital OUT value
  if(motion == 1){ // motion is detected
    digitalWrite(ledPin, HIGH); // light up LED
    Serial.println("MOVEMENT DETECTED"); //print to serial
  }
  else{ 
    digitalWrite(ledPin, LOW); // No motion, so LED is off
    Serial.println("NO MOVEMENT DETECTED"); //print to serial
  }
}

To follow up on this, these sensors are pretty sweet for how inexpensive they are..  Basically all I had wrong initially was to read the OUT digitally instead of analog and it works great.  No resistors, quite sensitive, and less dense objects won't prevent detection.  All you need is 3 wires, Vin (Supply), Gnd (Ground), and OUT (Output indicating motion), really simple -- here's my script, if this helps: 

const int sensorPin = 8; 
const int ledPin = 3; 
int motion; // Variable to read detection of movement

void setup() {
  Serial.begin(9600); 
  pinMode (sensorPIN, INPUT); 
  pinMode (buzzerPIN, OUTPUT); 
}
void loop() {
  motion = digitalRead(sensorPin); // Read digital OUT value
  if(motion == 1){ // motion is detected
    digitalWrite(ledPIN, HIGH); // light up LED
    Serial.println("MOVEMENT DETECTED"); //print to serial
  }
  else{ 
    digitalWrite(ledPIN, LOW); // No motion, so LED is off
    Serial.println("NO MOVEMENT DETECTED"); //print to serial
  }
}

After reading some on these, I think I strongly over-simplified their operation... I'm sort-of new to tinkering, so not surprised.  At least I've seen enough to say they're working.  I believe we'll need to incorporate some resistors/capacitors to fine tune the sensing.

It doesn't seem to pick up motion/movement like I expect, however if I pick up the breadboard it's attached to and move it - I get a clear change in readings.  It looks like I'm getting between 0-1023 from the OUT pin, so I set 600 as my trigger to turn an led on - this is working at least to indicate the sensor is moving so far (I also haven't soldered the pins yet, just have the sensor sitting on the pins).

I purchased some of these and there's a bunch of documentation on the site.  For reference, here's the link: https://market.alibaba.com/snapshotDetail.htm?contentId=1005012494

It appears the 3.3v is maybe to power another controller, but not needed in this sensor's use.  It seems to follow other sensor's in that Vin and GND power the sensor, OUT gives you the reading to indicate motion, and the CDS is used to power (or trigger) sensing.  That said, I just threw mine in a breadboard and am testing with an Arduino nano - I'm getting analog readings from OUT, but they don't appear to be very consistent yet.

Hello.

I wrote one article about this sensor:

http://blogmasterwalkershop.com.br/arduino/arduino-utilizando-o-sensor-microondas-rcwl-0516/

I put many details on the plate. I have done many researches and tests to write this article.

It's in Portuguese because I'm from Brazil. (Use Google Translate).

I hope you can help everyone.

I think Yann is close, but it's not Doppler but reflections of the radio wave changing the oscillator operating point. Just like the radio fuses in the WW2 bombs, see https://en.wikipedia.org/wiki/Proximity_fuze

If I'm right- Russian is not my native language- the module worked reliably on 3.3V from Arduino only if nothing else draw power from that line.

Some more there : https://www.reddit.com/r/arduino/comments/526b8s/anyone_have_experiance_with_microwave_radar/

BTW I don't think it sends pulses, it's probably a CW (Continuous Wave) that receives reflected signal. When the object moves, Dopler effect shifts the frequency. This frequency shift is measured by subtracting the reflected and the emitted wave, which should create a low-frequency signal, which is then decoded...

I'm trying to find more informations because these are usually microwave systems that are pretty interesting...