Inside a $1 radar motion sensor(10maurycy10.github.io) |
Inside a $1 radar motion sensor(10maurycy10.github.io) |
> Espressif claims it can also capture subtle movements caused by small movements such as breathing and chewing of people or animals in a static environment.. works with all ESP32 series microcontrollers including ESP32, ESP32-S2, and ESP32-C3, and does not require any changes to the hardware
2024 AI/NPU laptops with Wi-Fi 7 from Intel and Qualcomm can combine RF radar and on-device inference to identify human activity.
Related:
DIY Radio Telescope: Building a Camera That Can See WiFi (2019) https://www.youtube.com/watch?v=g3LT_b6K0Mc
Wi-Fi devices set to become object sensors by 2024 via IEEE 802.11bf standard (2021), https://news.ycombinator.com/item?id=40458766
How automotive radar measures the velocity of objects (2024) https://news.ycombinator.com/item?id=40768959
How Wi-Fi sensing of movement became usable (2024) https://www.technologyreview.com/2024/02/27/1088154/wifi-sen...
I use those for presence detection in my house. 3D print a small case and for < $20 you have highly accurate presence detection that also works when sitting still. Ideal for automatic light and climate control.
1. https://github.com/Marsrocky/Awesome-WiFi-CSI-Sensing#vital-...
NIST, "Monitoring Respiratory Motion with Wi-Fi CSI" (2022), https://www.nist.gov/news-events/news/2022/12/wi-fi-could-he... & https://doi.org/10.1109/ACCESS.2022.3230003
Google: Nest Hub sleep sensing for one person, with Fitbit Premium, https://www.techradar.com/health-fitness/how-to-track-your-s...
The ESP32 can detect the difference between a cannibal and a vegan?
That's impressive.
— kool aid man
I wonder what kind of resolution you can reasonably achieve? Is it good enough to detect finger pose?
Aside: is there a way around IEEE paywall? I'd really love to read some of these papers
I don’t know who designed this, but they were a master of the black art of Radio Frequency waveguide engineering. I am impressed. The PCB, itself, is a major component. Not only for the patch antennas but also several RF filters, the local oscillator, and the mixer are all largely made from peculiarly-shaped PCB tracks. Apart from the PCB, there are only five “components" on the board. Five passive components to implement a Doppler radar module. C’mon. You have to be impressed by that!Priced between 11 and 20 bucks they are fairly feature rich...
If you want to roll your own check out what the folks over at ESP home have going on (google esp home mm wave).
That said, it doesn't work very well for me when sitting still 4-5m away, it thinks I've left.
I'm sure there are more expensive options but they're more locked down/limited as well.
[1] https://www.cambridge.org/core/journals/international-journa...
[2] https://pubs.rsc.org/en/content/articlelanding/2022/tc/d1tc0...
I have an driveway alarm from mighty mule, which uses 433Mhz radio powered by two AA batteries to communicate signal from the coil sensor detection sitting next to the driveway to the base station in the house using OOK modulation. The stock PCB antenna was not very good at the distance I had it to work with, so I started experimenting with external antenna. I tried loaded antenna (i think it is what it is called - the one with the coil) and straight piece of wire.
I quickly realized that formula for 1/4 length is more of a starting point, and a lot depends on actual output components of the RC circuit (I have little to no understanding of how all of that works). I tried to cut slightly different sets of wires trying them next to HackRF/PortaPack showing me signal strength in the real time. Basically was eyeballing how strong and clear OOK bursts are, and how well or noisy they sounds through the built-in speaker... (again, I have no idea what I am doing...)
At some point I got tired of cutting wires and soldering them, so I tried to cut slightly longer wire and use thin piece of copper tubing to cover end of the antenna at various depth, hoping to simulate the antenna length changes. But at some point something weird to me happened - when just the tip of the antenna was covered by the tube, signal increased dramatically. I am talking about -55db - -50db to -36db on HackRF at the lowest usable gains settings...
I ended up with the antenna length slightly below 173mm ideal antenna length with a about 5mm-10mm "cap" made of aluminum foil tape (used for air ducts and such) at the very tip of the antenna. I also closed the other end of this wrap (in my imagination so that the signal does not escape this cap???). The cap itself is electrically disconnected from the antenna, it is just that - a cap.
I have no idea why it worked this way. I suspect by adding such a "cap" I modified something related to the capacitance or perhaps there is some resonance thing coming to play - no clue. But it became much more reliable at communicating over the distance I have it installed.
Perhaps someone who knows about such things, might give me a clue what I was dealing with.
Another thing that probably plays a role in this hack - outdoor transmitter is in the plastic box sitting vertically on a pvc pole, with batteries inside the same box. 1/4 straight antenna would not fit into it, but I also did not want to cut a hole at the top of the box to avoid water intrusion, so I pointed it down. But it also means it goes in parallel with the "USB" cable that connects to the coil-sensor next to the driveway. While system is not grounded, I suspect this USB cable is somehow became part of the antenna, since the best signal was when the line of sight between the antenna and base station, the usb cable was right behind the antenna. Distance between the antenna and usb cable running inside PVC pole is probably about 20-30mm.
If the Chinese government wants to undercut an American product, they will tell the manufacturer to drop the price to X, and the manufacturer will comply.
This also does not take into account Chinese currency manipulation.
Profit or loss be damned.
It’s not without flaws (regulatory approval is non-existent for this) but they really did combine some dirt cheap components on to a dirt cheap PCB.
You, too, could assemble this circuit at scale for extremely low prices, no government intervention necessary.
None of this is really true of the Chinese system.
Uber, AirBNB, etc ran at a loss to try to own the market.
The only mechanism besides ionization that could harm humans is through the transfer of lots of power into the human body (think soldiers keeping themselves warm by stepping in front of a radar emitter).
So let's try to do a ballpark estimate of how much that could matter.
I haven't found (from a quick search) any data regarding the transmission power, but the data sheet at https://fcc.report/FCC-ID/2AD56HLK-LD2410B-P/6620025.pdf says the average current consumption is 79mA at 5V, which means it uses 0.4W.
How much of that is actually transmitted? I'd guess 10%-50% (likely much less, but let's go with this more conservative estimate, from a safety perspective), so now we're in the range of 40mW to 200mW.
If you absorb 1/4th of that (again, somewhat conservative estimate; you'll likely also reflect some, and most of it is going to pass you), we're at 10mW to 50mW extra power that is absorbed by your tissue.
Again, this is a super high (and thus for our purpose, conservative) estimate. Somebody else in this thread mentioned microwatts being absorbed, which sounds much more plausible.
To put this into context, the base level of power that an adult human operates on at rest is about 100W. This is a factor of 500 to 2500 more than the power absorbed from our millimeter wave radar. Unless all the absorption happens by a very specific and sensitive part of the body (like your eyes or so), this should just be background noise.
If you want another perspective, you could try to compare it with whatever radiation (both RF and heat) that your phone emits, that you likely carry in your pocket for hours at a time.
This claim is, IMO, too strong given available evidence.
There are many chemical interactions with characteristic energies well below 1eV, or any reasonable threshold for "ionizing". Photons can couple with these interactions without ionizing anything. 4GHz range is probably fine, because the per photon energy is a small fraction of a mEv, but even then I would not rule out the possibility of multiple photons coupling to a structure without the imparted energy immediately being dispersed as heat.
Any time you have EM with low entropy/etendue, it is always theoretically possible for interactions to occur outside of the thermal regime.
Holy, did people actually do this? A quick search yielded no results. Not sure if thankful or not.
Probably overly careful, but I didn't want to point a radar at my sleeping kids (and myself) for 12 hours per day. Similar for the WiFi access point upstairs, it's only in the hallway and not at maximum power.
While I understand the sentiment. It's very very unlikely to be dangerous and there are plenty of other environmental dangers.
The biggest being the sun. But the most common man-made ones are probably auditory. Like toys and TVs being too loud or high-frequency sounds blasted from speakers in malls or under bridges to avoid "loitering."
For example: maybe the ESP32 transmitting the bed weight exposes us to more danger than the radar sensor (that can also be placed very far from the bed)? Maybe with our smartphones charging on the nightstand too.
I’m not a big fan of fear-based, illogical decisions. But, again, I understand perfectly.
Also note, if you are just receiving signals you have more freedom to experiment. Antenna tuning matters a lot more when transmitting (especially at larger powers). (Not implying that it doesn't matter with reception)
I have had decent success with them when finetuning antennas for lower bands.
Even tape or insulation from a wire can, be used to electrically lengthen or fine tune an antenna. But thats less about capacitance and more about the electrical lenght being longer in the dielectric.
Sounds like you might have inadvertently created a wave guide.
If you are feeling adventurous you might want to try dropping your creation into an Antenna Simulation software like NEC or something similar.
Here is youtube video someone fixing broken unit to get an idea what it looks like inside - https://www.youtube.com/watch?v=-k_6NsqFAdc
Not sized properly. Transmitter is sitting on a pretty tall pole right now and getting it off is a bit of a hassle. And I also already covered cap with a glued heatshrink to protect against elements, so accurate measurements are not possible without destroying it... But I hope it can give an idea what I came up with.
Thanks for the link to the simulation tool!
The US government invests in growing the economy, or tries to, which increase tax revenue which gives the government more money.
edit: Also it's not that top VCs are better at finding investment but rather that their social capital means they provide values to companies beyond the investment money. As a result companies that are doing well which choose to take money from top VCs versus other VCs. As a result the model doesn't scale since there's a limited pool of top companies to invest in.
On the homepage, there is a video [2] explaining more as well, and their paper [3].
1. https://www.rouast.com/vitallens/
Presence (commercial): https://community.intel.com/t5/Blogs/Tech-Innovation/Client/...
Breathing (research): https://www.intel.com/content/www/us/en/research/respiration...
For older Intel wifi radios, there is custom firmware and many research papers: https://dhalperi.github.io/linux-80211n-csitool/
But the effects are debated and not entirely scientific: https://www.reddit.com/r/army/comments/13r6hod/i_keep_being_...
https://en.wikipedia.org/wiki/Microwave_oven#Discovery
The thing is, you don't need a lot of extra heat to melt a chocolate bar on your pocket. It's perfectly possible that everybody felt hot when working on an active radar, but didn't discuss it or maybe even notice the correlation.
> The first food deliberately cooked with Spencer's microwave oven was popcorn, and the second was an egg, which exploded in the face of one of the experimenters.
They were having a blast I see.
I wrote low level drivers for the ESP32 for all the ones I could buy and have tested all of them. The only one that does not try to give a human occupancy position is the car speed sensor.
The ld2450 can track three people at once.
I have another more complete project for just the 2450 in another repo for the esp-idf with wifi provisioning and publishes presence to mqtt. I have 3 of these around the house.
There are more Americans with gambling addictions than there are people committed to vegan diets!”
Chart: https://x.com/cremieuxrecueil/status/1805367282270433791?s=4...
The later group used to be larger, but I don't remember anybody doing that recently.
Still, I'm not sure if it's a big factor. You likely know who is vegan in your circles, because veganism is unusual enough to be a good topic for gossip, you can easily see it when sharing a meal with someone, and it's also something you'd like to know when inviting people over, if you want to be a good host. So I think a more relevant estimate would be number of vegans you know vs. how many of them announce their veganism at the earliest opportunity.
Seems like it'd be finicky though.
Detection range without obstacles depends on transmit power and signal reception.
There are other models in the same family which might have more power/range.