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:
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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:
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On the other side of the board is a description of the leads:
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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.
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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 .
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?
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. What is the situation with this detector? Does this type of detector also generate false alarms?
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. Microwaves penetrate wooden doors and thin walls. Movement in the corridor or in the neighbouring room can be detected.
The module costs £5. It would be worth comparing the capabilities of a more advanced device.
This detector is suitable as a presence detector while in alarms I prefer a proven PIR. This detector can be interfered with by a second £5 module tossed into the area of operation and triggered at random times.
Car alarms have used ultrasonic motion detectors inside the cabin. Interestingly, I have seen a dog react to the activation of a 40kHz ultrasonic transmitter. He was not frightened, but clearly interested and looked towards the transmitter.
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 reduction function, but from information gathered from the internet, it seems to have reduced the detection zone, which doesn't necessarily translate into reduced sensitivity. I've had it installed in a home workshop for over a year (thick walls, no Wi-Fi, even GSM drops heavily) and it works perfectly, detects a wandering cat, zero false alarms. But already with plasterboard walls or ordinary brick it detects people behind the wall. If it could be desensitised it would be an ideal PIR alternative.
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 specialised microwave sensors operating on 24GHz that detect heartbeat or breathing without contact.
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 and resistance to interference?
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 the wooden stairs under the first and last step, it turns on the WLED illumination along the stairs.
I wanted to add that adding a 120 Ω resistor in parallel to R9 on the board reduces the range to 30-40 cm
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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?
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 behind obstacles like wood or cardboard, which can block or attenuate PIR detection.
Typically, microwave motion detectors like the RCWL-0516 operate in the frequency range of 2.4 GHz to 24 GHz. The RCWL-0516, as you mentioned, operates at around 3 GHz, which is within the lower range of this spectrum. Higher-frequency sensors, especially in the 24 GHz range, offer more precision and shorter detection ranges but can be more sensitive to environmental factors.
Microwave sensors are often preferred in environments where you need detection through non-metallic obstacles, whereas PIR sensors are better in open areas where you want precise detection based on heat signatures.
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 not depend, the wires from the power supply extended to eliminate their influence.
The boards are the same as in the article, soldermask description, resistors. The circuits are from 2021, if this is the production date.
The RCWL-0516 is a microwave motion detector that operates at approximately 3GHz, utilizing the Doppler effect to detect movement through obstacles like wooden furniture, unlike traditional PIR sensors. Users have noted its lower sensitivity compared to PIR detectors, with better performance for faster movements and a detection range of 5-7 meters. Concerns about safety and false alarms were raised, particularly due to the potential for interference from other devices operating in similar frequency bands, such as Wi-Fi routers. Some users have successfully modified the detector to reduce its range and improve functionality in specific applications, such as under stairs. The discussion also touched on the potential for using higher frequency sensors for improved sensitivity and the possibility of shielding the detector to enhance directionality and reduce interference. Summary generated by the language model.
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