I purchased a few RCWL-0516 microwave presence sensors to switch on an extraction fan. The sensor was intended to be placed in the false ceiling space above the Gyproc in the shower. The sensor tested perfectly thru a piece pf Gyproc in my living room after adjusting the sensitivity resistor, however when placed in the confined space above the shower ceiling it false activates continuously, even at lowest sensitivity. I have tried screening the back and sides of the sensor, but this has not helped. I am unaware of any interference as nearby fans and downlights were switched off.
Has anybody had experience of this issue, and how it may be resolved?
Thanks, Richard
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Hi Richard,
Does the behaviour still happen when the sensor is used in the same space but not behind the Gyproc?
It does use a frequency outside of normal Bluetooth and Wifi so they shouldn’t be an issue.
Different materials have different election and absorption capabilities so I’m wondering if the shape/materials of the room are causing a stange reflection that is being detected as a person.
Hi Richard
The gyproc in the ceiling wouldn’t be of the insulating kind with an aluminium sheet backing by any chance would it.
Anyway although the product splurge is delightfully empty of any technical details it is likely to be operating in the several GHz range and you got lucky with your original piece of gyproc. Being Radar anything solid should reflect the signal. If the text is correct and this is Doppler Radar the target will have to be moving toward or away from the sensor.
Cheers Bob
Thanks for your comments Aaron.
Yes, the same behaviour occurs if the sensor is below Gyroc.Yes, the small bathroom is fully tiled except the ceiling, so it seems that excessive reflections may be triggering the sensor even though there is no movement.
I have tested 3 of these sensors and they yield the same results.
I have ordered another microwave sensor with a more directional patch antenna in the hope it may perform better in my bathroom environment.
If that doesn’t work then I intend to try an IR sensor through the Gyproc ceiling, which is not ideal.
Bob, both my test piece of Gyproc and the bathroom ceiling do not have an aluminium layer.
I believe the sensor frequency is 3.2GHz, which should penetrate Gyproc, according to several websites.
Hi Richard
3.2G, that is somewhere the “10cm” radar used on large ships. I was looking at the physical size of the antenna on the units PC board. Looks more like about 10GHz. Where did you get the 3.2GHz from?
Marine radar (which is Pulse Echo as against doppler) has one shortcoming called sea clutter which manifests itself as speckles on the display. Caused by white caps on the sea in windy weather so the target can be really made of anything. This is more prevalent in the higher frequency 3cm (10GHz) units. That is why I find it strange that you say it worked perfectly through a sheet of Gyproc. I don’t think it should have.
Cheers Bob
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Hi Bob, Raspberry Pi Pico RCWL-0516 Microwave Radar Proximity Sensor Arduino IDE | Random Nerd Tutorials and All About RCWL-0516 Microwave Radar Motion Sensor : 15 Steps - Instructables both say the frequency is 3.8GHZ and can penetrate non metallic materials.
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Hi Richard
3.18GHz NOT 3.8GHz
Yes the incident wave might but the reflections could be anything. If you were using this for point to point communications yes it might be OK but if you are expecting reflections as in radar I believe you need free air line of sight so you can have some control over what is happening.
Some of the text in that link is a bit strange. Early in the article it says it detects “any objects” (as long as the object is moving) which means you will get a reflection off “any object”. Fair enough, that is OK.
Later it says it works through walls etc. The author should make up his mind here. Even though the wall is not moving WRT the radar unit it will still reflect a signal which would probably be strong enough to override any reflected signal from a moving object on the other side of the wall. The article says this unit works through walls without any degradation in performance. Leave me out of it, Any reflected signal off an intervening wall must surely confuse the issue somewhat. A bit hard to predict with any certainty exactly what would happen here.
My humble thoughts. Save yourself some trouble and don’t operate through a wall.
Cheers Bob
It would be interesting to see some performance numbers on that antenna at 3.2GHz
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Have you tried any type of shileding to solve this problem?
Hi Lia
Just what are you going to shield. You would probably stop it working altogether. There again that might solve all the problems.
Cheers Bob
Hi Richard
Sorry for being a bit slow but just noticed that bit.
If it does that how are you going to detect people movement. Unless the people are wearing a suit of armour they would definitely come under the “non metallic” category.
Cheers Bob
It seems to be 3.18GHz anyway but close enough.
Hi All
Nowhere can I find any information on the radiation pattern of this device or the best orientation when mounting.
Anyone got any info re this???
Cheers Bob
Unfortunately, there isn’t much out there I can find. The best that I could pull up was articles talking about “360-degree detection area without blind spots.”
I’m not sure if there would have been radiation pattern tests done on this device in all honesty.
I need to try a more directional microwave sensor such as this..
I also intend to try a humidity sensor instead, but I’m currently battling to load library for the DHT11.
Hi Aaron
Afraid I don’t quite believe that. This implies that this device is in the centre of a sphere and transmits in all directions. Don’t think this can happen. There will be a horizontal and vertical pattern WRT the device orientation.
Consider the simplest antenna. A 1/4 wave vertical dipole. The radiation pattern will be circular in the horizontal direction (or omni directional)but in the vertical will be a circle on either side of the dipole to if you looked at a 3 dimensional model would look something like a doughnut with a very small hole. Straight up…NOTHING. This area known as the “cone of silence” which will happen with any vertical antenna. Even with a simple horizontal half wave antenna there will be zero radiation out the ends or in the direction of orientation.
I believe all antennas are modifications or fiddles with the simple dipole. Sure you can fill in the gaps and do what is termed “null fill” with multiple elements fed in a phase controlled manner to adjust this null fill and beam angle but I find a spherical pattern as implied a bit hard to believe.
I might add that frequency has nothing to do with all this. It just changes the physical size of the bits and maybe some techniques.
So the question remains. What is the optimal orientation for this board. Or do you just mount it somehow and hope for the best.
Cheers Bob
