Radar motion detector

I needed a motion detector for Arduino. I saw a cheap Microwave Radar Induction Switch Human Motion Sensor Module at DX (similar also available at Banggood at pack of 5). It advertises High Sensitivity for Arduino, Long Sensing Distance, Wide Sensing Angle for Detecting Moving Objects.

Using this is a microwave sensor module that specifically for detecting moving objects and human body. It uses  uses Doppler radar technology, a technology that I tested with other module at my HB100 microwave radar to Arduino posting. This module promises advantages such as high sensitivity, long sensing distance, wide sensing angle, high reliability, wide range of operating voltage. It is designed to be used in human body sensing lighting system and anti-theft alarm system (as an alternative to the common PIR motion sensors).

The working voltage range is 4-28VDC with operating current less than 3 mA. The module outputs 3.3V digital signal that is on or off based on detection. Those specifications are such that the module can be directly interfaced to Arduino board that used 5V voltage (connect GND / OUT / VIN). . That 5V is right operating voltage for module, and the 3.3V digital output works OK with Arduino AVR chip operating at 5V digital input. The module has also 3.3V regulator that did not test.

The module promises detecting range of less than 120 degrees taper angle within 7 meters. The module works well up to few meters distance (I did not try longer distance). The trigger mode s repeat trigger and the delay time is 2 seconds (option to change value). When this radar module triggered by moving object, its TTL-level output (OUT) pin switches from LOW (0 V) to HIGH (3.3 V) for a finite time (around 2 seconds) before returning to its idle (LOW) state.

Soldered wires


3V3……….Regulated output (reference only)
GND………Ground / 0V supply input
OUT……….Trigger: HIGH (3.3V) motion detected / LOW (0V) idle
VIN………. 4V-28V supply input
CDS……….Sensor disable input (pull low to disable)


Here are some videos on this and similar radar modules:

Amazing $1 microwave RF motion sensor board review and test


Coolest motion detection sensor ever!


#135 Radar Sensors / Switches: Comparison and Tests


Doppler Radar – and how it works


RCWL-0516 Microwave Radar Sensor Arduino Distance Test and Review

How this device electronics works? It was a little hard information available for this (eg even the operating frequency is left unstated on product page). But after some Google searching I found some useful information bits.

Electroschematics RCWL-0516 page gives some details on the technology of the module:

Key features:

Supply Voltage: 4–28 VDC

Operating frequency: ~3.2 GHz (observed by me at my lab)

Transmit power: 20 mW (typical)/30 mW (max)

Sensing Distance: 5–7 m

Stackexhange posting on rcwl-0516 module tells that the operating frequency is 3.181GHz! RF part of this has surprisingly few components (what looks like a MMBR941M NPN and a hand full of passives) and the microwave magic could be in the PCB design. There is a GitHub repository on module information at https://github.com/jdesbonnet/RCWL-0516. Also Hackaday has some information on this module.

MPJA page says that this detects human motion even thru an interior wall! Range about 20 feet, bigger objects perhaps further. Hobbycomponents page says that HCSENS0040 device operates at ~3.2GHz/20 – 30mW. In some countries it may be illegal to operate this device. Component side should face detection area for maximum sensitivity. Do not place metal objects within 1cm of antenna. I am not sure would this device fall within ETSI Short Range Devices definitions and would the used frequency OK to use.

Investigating a RCWL 9196 / RCWL-0516 “Radar” motion detector module page provides this nice circuit diagram of the device (similar to one on this data sheet):

Based on the schematics – the transistor works as a free running UHF oscillator, the changes in its collector current are filtered by R3 C9 low pass filter and fed into the chip. Whatever the chip does, it is quite simple design.

A microwave frequency transmitter/receiver/mixer and a much lower frequency part based on an IC (marked RCWL-9196) which is very similar to the BISS0001 IC used in PIR motion detectors. For idea how the microwave part of this works, check the patent EP3091605A1 that describes similar device that operates at 5.8 GHz. At the heart of the RF is a Q1 a MMBR941M high frequency NPN transistor in what is probably a Colpitt oscillator confguration and works as mixer for difference between the transmitted and reflected signal. The core of the low frequncy signal processing is an IC marked RCWL-9196. For some more details, check this RCWL-0516 document.




  1. Tomi Engdahl says:

    The still unanswered question is that would using this device be legal as small power radar?

    Or is this considered as illegal RF noise source that disturbs something important?

  2. Tomi Engdahl says:

    Intelligent Sensors using 24GHz Radar Technology

    Getting started with Infineon’s development kit SENSE2GOL

    Infineon’s range of radar offerings provide unique benefits not possible with traditional motion sensing technology (passive infrared technology, camera based systems) such as increased range coverage, small form factor solution or object detection while keeping identities anonymous.

    The BGT24LTR11 can be found at the heart of Infineon’s radar sensor portfolio. Synonymous with ultra-low power sensing using a new generation of 24GHz radar technology it operates perfectly also under harsh (weather) conditions. The low power radar transceiver combines one transmit and one receive channel. It is currently the smallest 24 GHz MMIC in the market.


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