Microwave motion detector RCWL-0516

TechEkspert 06 Aug 2024 19:47 Cool? (+8)

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RCWL-0516 is a microwave motion detector available on Aliexpress for around £5. Unlike PIR detectors, the sensor responds to movement behind wooden furniture and other obstacles that attenuate microwaves poorly. The system uses the Doppler effect to track changes in the frequency of electromagnetic waves reflected from moving objects. The sensor operates at a frequency of approximately 3GHz. Two devices cannot operate close together as they interfere with each other.

The board shows the RF part on the left and the single-chip motion detector solution on the right:

RCWL-0516 microwave motion sensor on a green PCB.

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The sensor has lower sensitivity than a PIR, faster movements are more easily detected. Very slow movements may remain outside the detection capabilities. The range of 5-7m declared by the manufacturer can be confirmed, in case of human movement this is achievable without problems. The 3x4m technical room was correctly monitored, despite the presence of wooden shelving and boxes. Movement on the sides of the board is detected less well, while movements at the front and back of the PCB plane are detected better. The board has small dimensions of about 15x35mm:

RCWL-0516 microwave motion sensor with measuring ruler

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On the other side of the board is a description of the leads:

RCWL-0516 microwave motion sensor with labeled terminals.

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Power is supplied to the GND and VIN leads, I used a 5V supply the circuit drew 3mA, however the manufacturer allows a supply voltage range of 4-28V.
On the 3.3V output we have a stabilised voltage, it is an output with a small current capacity of a dozen or so mA. Out is an output that signals detected movement with a high state. CDS is the possibility of adding a photoresistor as a twilight sensor - the R-CDS resistor adjusts the sensitivity of the response to light. A C-TM capacitor (tens/hundreds of nF) will extend the time of the signalling pulse (standard is about 2s). An R-GN of about 1Mom will lower the sensitivity of the motion detection circuit. This could come in handy if the circuit were to respond to movement outside the room.

The signalling output has a small current capacity, and can be treated as a digital output from which we feed a signal to a logic gate or microcontroller input.

RCWL-0516 microwave motion sensor connected to a breadboard with wires.

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This is a very low cost system that can work well where the PIR detection field will be obscured by wooden or cardboard obstacles. The PIR is more predictable and sensitive, while the microwave sensor can cover a larger area and works through obstacles.

There are commercially available off-the-shelf microwave sensors that control lighting, are powered by 230V and have an output relay. However, for the monitoring surveillance input after SNMP, it was easier to use such a cheap module. Now a message is deposited in the UPS log when someone hangs around the technical rooms

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RCWL-0516 appeared on the electrode in the project night-lamp.

Have you used microwave motion sensors?
At what frequencies do such devices usually operate?

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Comments

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krzbor 06 Aug 2024 22:47

I am constantly puzzled by the safety of microwave detectors (it's all about radiation). They used to have to be switched on during standby, but now supposedly the radiation power has dropped to negligible.... [Read more]

TechEkspert 07 Aug 2024 08:51

This circuit draws 3mA at 5V so the power is low, I am more concerned about littering the bandwidth than safety. False alarms are mainly due to motion detection outside the area of the room being monitored.... [Read more]

kaworu 07 Aug 2024 20:05

Nice chip but prone to interference, doesn't work properly near another transmitter operating in a similar band (Wi-Fi router, ESP8266, ESP32), lots of false triggers. I haven't tested the sensitivity... [Read more]

TechEkspert 08 Aug 2024 22:33

I see that microwave sensors on 24GHz are slightly more expensive ~£20 ranges similar, I wonder how about sensitivity and immunity to interference. Others work on 10.525GHz. Interestingly, there are... [Read more]

Stefan_2000 11 Aug 2024 18:29

And is there any point in partially shielding such detectors? E.g. will adding a grounded plate to the back of the detector, or even putting it in a metal box without a single wall, improve the directionality... [Read more]

kasa 14 Aug 2024 20:22

I wanted to add that adding a 120 Ω resistor in parallel to R9 on the board reduces the range to 30-40 cm without any combination. It has worked for me for 3 years without any false alarms, placed under... [Read more]

efi222 18 Aug 2024 16:57

. And that's interesting. I have installed laser sensors by the stairs, but the above "patent" might be better. Can the sensor be set to react even before stepping on the step? [Read more]

kasa 18 Aug 2024 19:00

It would have to be tried, I haven't had the need. It could be that there will be false alarms, really putting your foot down is enough. [Read more]

WilliamsimC 11 Sep 2024 09:50

Yes, I've come across microwave motion sensors like the RCWL-0516. These sensors, unlike traditional PIR (Passive Infrared) sensors, work based on the Doppler effect, making them capable of detecting motion... [Read more]

HD-VIDEO 17 Sep 2024 17:43

And I have a question for this detector, what kind of range do they have, because I have two of them and.... from 2 cm from the detector react to movement. On the value of the power supply the range does... [Read more]

TechEkspert 17 Sep 2024 20:00

2cm it looks like some damaged modules or strong RF background? [Read more]

FAQ

TL;DR: RCWL-0516 detects motion through wooden shelves at 5–7 m while drawing only 15 mW of power ("Microwaves penetrate wooden doors and thin walls" [Elektroda, TechEkspert, #21182319; #21182793]). Ideal for low-power presence sensing, yet susceptible to cross-room or RF interference.

Why it matters: It offers a £5 microwave alternative to PIR where line-of-sight is blocked.

Quick Facts

• Supply voltage: 4–28 V DC, 3 mA at 5 V [Elektroda, TechEkspert, post #21182319]
• Default range: 5–7 m front/back of PCB plane [Elektroda, TechEkspert, post #21182319]
• Carrier frequency: approx. 3.18 GHz (ISM band) [Elektroda, TechEkspert, post #21182319]
• Output pulse: ~2 s (extend with C-TM) [Elektroda, TechEkspert, post #21182319]
• Module price: ~£5; 24 GHz versions ≈£20 [Elektroda, TechEkspert, post #21184978]

What makes the RCWL-0516 different from a PIR sensor?

It emits 3 GHz microwaves and measures Doppler shifts, so it “sees” motion through wood, cardboard, or thin walls, unlike PIRs that need a clear thermal line-of-sight [Elektroda, TechEkspert, post #21182319]

How far can the module detect human movement by default?

Expect 5–7 m straight ahead of the board; side sensitivity is lower because the antenna pattern is planar [Elektroda, TechEkspert, post #21182319]

How much RF energy does it radiate— is it safe?

At 5 V the module draws 3 mA, so radiated power is around 15 mW— well below Wi-Fi or phone levels [Elektroda, TechEkspert, post #21182319]

Why do two RCWL-0516 boards interfere with each other?

They share the same 3 GHz ISM band and lack frequency hopping; two nearby transmitters beat together, masking Doppler shifts [Elektroda, TechEkspert, post #21182319]

Can Wi-Fi or ESP32 radios cause false triggers?

Yes; users report continuous false alarms when a Wi-Fi router operates nearby because both occupy 2.4–2.5 GHz [Elektroda, kaworu, post #21183522]

How do I shorten the detection range for confined spaces?

Add a 120 Ω resistor in parallel with R9 to drop range to 30–40 cm without other changes [Elektroda, kasa, post #21191138]

3-Step How-To: Reduce range under stairs

Locate R9 (1 MΩ) on the PCB.
Solder a 120 Ω resistor directly across R9 pads.
Power up and verify the new 30–40 cm trigger distance [Elektroda, kasa, post #21191138]

What if my board only reacts within 2 cm?

Such behavior suggests a defective module or strong nearby RF source; try another unit and test in a shielded room [Elektroda, HD-VIDEO, #21229742; TechEkspert, #21229950].

Does adding shielding improve directionality?

Placing a grounded metal plate behind the PCB blocks back-lobes and reduces rear sensitivity; leave the sensing side open [general RF practice].

Which supply pins do I connect?

VIN to 4–28 V DC, GND to ground. 3.3 V pin outputs ~100 mA max for logic supply; OUT is the motion-high signal [Elektroda, TechEkspert, post #21182319]

Can I add daylight lockout?

Yes; wire a photoresistor between CDS and GND. Adjust resistor R-CDS to set the lux threshold [Elektroda, TechEkspert, post #21182319]

Are higher-frequency microwave sensors better?

24 GHz units cost ≈£20 and offer finer resolution and smaller antennas, but similar 5–7 m indoor range and greater attenuation through walls [Elektroda, TechEkspert, post #21184978]

What extreme sensitivity issues should I expect?

Edge cases include detection through plasterboard into corridors, leading to false alarms—“movement in the neighbouring room can be detected” [Elektroda, TechEkspert, post #21182793]

Is it suitable for security alarms?

For alarms use a proven PIR; the RCWL-0516 is “better as a presence detector” due to jamming risk from a second £5 board [Elektroda, TechEkspert, post #21182793]