I have a Athom PS02C3MZ presence sensor that uses the HLK LD2450 mmWave sensor. This sensor has a 6.0m range.
I got this with the Athom ceiling mount - however, I’ve now found out that apparently the LD2450 is recommended to be wall-mounted…not ceiling mounted.
Apparently with the ceiling mount, the range is around 2.0 meters - but if you wall mount it, you get the full 6.0m range. I was curious why this is - possibly I’m missing something very obvious about angles here?
I taped these temporarily to the ceiling, and used the HLKRadarTool app to do some tests. The ceilings are around 2.3m high - and yes, you basically do only get the 2.0m range, for some weird reason. It can’t detect people who are further out - it just loses tracking on them.
But if you put the sensor around chest heigh facing outwards - you do get 4-5 metres of range - and it does seem to nearly get 180 degree coverage as well.
Does anybody know why the ceiling mount position is so much worse, or why the angle of coverage seems less?
I believe the LD2450 is built more for wall mounting as the radar signal is more targeted towards the front of the sensor so it has a much better range for distance. Its not great at the wider angles and above and below. So when mounted on the ceiling, the range of the sensor becomes how wide the 360 coverage of the sensor is (ie. left/right/above/below) hence the poor range.
Think if it like a torch light. It lights up straight in front of you but around you, its fairly dim. Think of the radar as similar to the light from a torch.
Consider the image a radar would see from persons from
the side
the top
both are some much different in shape, that the software (firmware) needs to be competely rewritten for those profiles.
This is also the reason that a top located sensor is very good in ‘fall detection’ as the shape of a dot changes to person shape.
Top scanning is just hard to make presence detection precise enough
@athua I know for wifi APs (and other RF transmitters etc), the datasheet will typically give you a radiation diagram or polar plot, so you can see the signal propagation through free space:
Does anybody know if there’s something similar for the LD2450, or other mmWave sensors? (Or I guess, whatever the equivalent to a RF radiation diagram here is).
The closest I can find is on page 14 of the user manual - but I’m not sure what the diagram means?
@checking12 Yeah - fair enough - I guess if you see it from a profile view - top of head is harder to find vs getting a proper view of the whole person side on =).
It’s a bit annoying, as now I have a bunch of Athom presence sensors with the ceiling bracket - and it seems the ceiling bracket might be useful .
And Apollo also make a deal of having the ceiling mount:
It’s weird though - why would they sell them, if the mmWave sensors aren’t designed to be ceiling mounted at all?
Or is there some tweak to at least make the ceiling positioning slightly better?
.