[HN Gopher] Inside a $1 radar motion sensor
___________________________________________________________________
Inside a $1 radar motion sensor
Author : nothacking_
Score : 559 points
Date : 2024-06-30 00:44 UTC (22 hours ago)
(HTM) web link (10maurycy10.github.io)
(TXT) w3m dump (10maurycy10.github.io)
| transpute wrote:
| Through-wall 2.4Ghz Wi-Fi CSI radar can be done with $20 ESP32
| boards, https://github.com/Marsrocky/Awesome-WiFi-CSI-Sensing &
| https://www.cnx-software.com/2022/08/08/esp-wifi-csi-detects...
|
| _> Espressif claims it can also capture subtle movements caused
| by small movements such as breathing and chewing of people or
| animals in a static environment.. works with all ESP32 series
| microcontrollers including ESP32, ESP32-S2, and ESP32-C3, and
| does not require any changes to the hardware_
|
| 2024 AI/NPU laptops with Wi-Fi 7 from Intel and Qualcomm can
| combine RF radar and on-device inference to identify human
| activity.
|
| Related:
|
| DIY Radio Telescope: Building a Camera That Can See WiFi (2019)
| https://www.youtube.com/watch?v=g3LT_b6K0Mc
|
| Wi-Fi devices set to become object sensors by 2024 via IEEE
| 802.11bf standard (2021),
| https://news.ycombinator.com/item?id=40458766
|
| How automotive radar measures the velocity of objects (2024)
| https://news.ycombinator.com/item?id=40768959
|
| How Wi-Fi sensing of movement became usable (2024)
| https://www.technologyreview.com/2024/02/27/1088154/wifi-sen...
| throwup238 wrote:
| _> chewing of people or animals_
|
| The ESP32 can detect the difference between a cannibal and a
| vegan?
|
| That's impressive.
| lopis wrote:
| How can you tell someone is a vegan? Don't worry, this 1$
| radar motion sensor can tell you.
| silisili wrote:
| I think you could go cheaper. A sound detection sensor is a
| bit cheaper, and it just needs to detect the word 'vegan.'
| tstrimple wrote:
| Strangely enough I've heard far more people make this
| "joke" than actual vegans speaking up. Even when living
| in LA.
| stavros wrote:
| The issue with this joke is that it's 100% confirmation
| bias. You know that all the vegans tell you they're vegan
| because you don't know about the ones that didn't.
| LoganDark wrote:
| I think it's also survivorship bias. All the people who
| tell you they're vegan being vegan does not mean that all
| the people who are vegan will tell you they're vegan,
| just like all the people who won the lottery probably
| having bought lots of tickets does not mean that buying
| lots of tickets will win you the lottery.
| stavros wrote:
| That's what I meant, maybe I used the wrong bias name.
| TeMPOraL wrote:
| I know this under "selection bias", so now we have three
| contenders.
|
| 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.
| LoganDark wrote:
| I believe survivorship bias is a specific type of
| selection bias.
| LoganDark wrote:
| Confirmation bias typically refers to accepting very
| little evidence or rejecting disproofs. Survivorship bias
| is the one where you forget to account for the non-
| survivors of a particular selection criteria.
| marcosdumay wrote:
| There are people that I discovered were vegans when
| discussing what to eat. And there are people that loudly
| announced they'd become vegans without any context.
|
| The later group used to be larger, but I don't remember
| anybody doing that recently.
| nothacking_ wrote:
| That's the trick, you invert the logic. If you hear the
| word vegan, assume the person saying it is not.
| 01100011 wrote:
| It made more sense 20 years ago when it was more
| generally true. Veganism seems to have spread beyond the
| merely self-righteous now. It's a very old joke (possibly
| from the 90?s).
| NavinF wrote:
| "Practically everyone knows what veganism is, but vegans
| are actually a very small minority.
|
| There are more Americans with gambling addictions than
| there are people committed to vegan diets!"
|
| Chart: https://x.com/cremieuxrecueil/status/1805367282270
| 433791?s=4...
| the_third_wave wrote:
| Come on, that's simple, just use voice recognition since
| the vegan won't stop telling the sensor about it.
| slicktux wrote:
| Great links! I recall seeing somewhere that AMEX was investing
| in WiFi object detection...can't remember exactly for what or
| how...
| t0mas88 wrote:
| Wifi sensing is interesting, but you can combine a $3 ESP chip
| with one of these for a much easier project at lower cost:
| https://www.dfrobot.com/product-2795.html
|
| 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.
| stavros wrote:
| My problem with similar sensors is that they don't work very
| well if you're sitting still around 3m away. Maybe my sensor
| isn't great, but when I'm sitting still at the computer, it
| frequently thinks I'm not there any more, which ruins any
| benefit.
| squarefoot wrote:
| Pairing them with PIR detection should help to also detect
| stationary warm objects.
| stavros wrote:
| I did pair them, unfortunately PIR sensors are even worse
| at detecting stationary objects (less sensitive to body
| micromovements).
| Avamander wrote:
| It's difficult to find good PIR sensors though. The
| commonly found cheap modules don't include a thermistor
| to compensate for room temperature. Finding one with
| analog output or continuous detection is even more
| difficult, most detect changes.
| Avamander wrote:
| There are some that detect heartbeat, I guess those might
| work. But those are mmWave, not just cheap 2.4GHz radars or
| PIR.
| stavros wrote:
| I've got LD2410B, which are mmWave, so they should detect
| heartbeat (and do), but not from more than 2-3m away.
| transpute wrote:
| Is the LD2410B sensing range limited by the PCB antenna?
| stavros wrote:
| I'm not sure, it always just made sense to me that the
| farther away someone is, the harder it'll be to detect
| their small movements.
| transpute wrote:
| Smallness detection depends on RF: higher frequency =
| shorter wavelength = more resolution for imaging.
|
| 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.
| victorbjorklund wrote:
| A hack is to put a sensor on the chair
| stavros wrote:
| Hmmmmm that's not a bad idea, I'll have to see how to do
| that, though. I don't want cables restricting me.
| swsieber wrote:
| If your fine with zigbee, I could see having one of these
| aqara door sensors in the cushion of the seat, triggering
| to closed when you sit on it:
| https://cloudfree.shop/product/aqara-door-and-window-
| sensors...
|
| Seems like it'd be finicky though.
| stavros wrote:
| Zigbee is great, but my chair has a mesh :/ I'll see if I
| can print something below, so that the sensor is
| activated, but yes, it does seem that it would be pretty
| finicky...
| transpute wrote:
| Ceiling sensor is another option.
| stavros wrote:
| For now I've put a mmWave sensor under my desk, which
| works fairly OK. It's not perfect, but definitely good
| enough.
| rpgwaiter wrote:
| You can buy the sensors they use in car seats for like
| $10 https://a.co/d/0dibAFxc
| mytailorisrich wrote:
| I solved the issue by linking my lights to a switch that
| I turn on when needed. It has worked very well so far,
| with no false detection at all!
| banku_brougham wrote:
| plz let us know how it goes after sufficient testi g
| 037 wrote:
| The "Vital Sign Detection & Healthcare"[1] section is very
| interesting, thank you! I am looking for a way to measure the
| heartbeat of a single person in a completely non-invasive
| manner (so without contact) and I see that it can be done with
| Wi-Fi (2019 Paper [2]). However, I've noticed that there are a
| lot of methods (video analysis, thermal camera, etc.), but they
| are hard to find as ready-made products at a reasonable price.
| The simplest solution is under-mattress sleep trackers, but
| unfortunately they are not an option for me.
|
| 1. https://github.com/Marsrocky/Awesome-WiFi-CSI-
| Sensing#vital-...
|
| 2. https://arxiv.org/abs/1908.05108
| amelius wrote:
| Interesting. I'd be interested in a breathing sensor that can
| work on someone working at a computer.
| 037 wrote:
| I'm sure it can be done with a normal camera and enough
| light, especially with the advancement of AI technologies
| in recent years. I haven't had time to experiment, but if
| you have an iPhone, you can try this app [1] I installed
| yesterday to study its feasibility.
|
| On the homepage, there is a video [2] explaining more as
| well, and their paper [3].
|
| 1. https://www.rouast.com/vitallens/
|
| 2. https://www.youtube.com/watch?v=_0HHjovI8hc
|
| 3. https://arxiv.org/pdf/2312.06892
| transpute wrote:
| Intel Meteor Lake+ platforms can use NPU for WiFi 7
| Sensing.
|
| 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/
| transpute wrote:
| _> measure the heartbeat of a single person in a completely
| non-invasive manner_
|
| 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...
| amelius wrote:
| These $1 boards also work through walls (I tried this).
| withinboredom wrote:
| I always go through walls.
|
| -- kool aid man
| roger_ wrote:
| You can also use a single ESP and your WiFi AP as a source of
| packets.
| utensil4778 wrote:
| The gesture recognition sounds incredibly interesting. I work
| with vision based band tracking, and performance really isn't
| good enough for my application.
|
| I wonder what kind of resolution you can reasonably achieve? Is
| it good enough to detect finger pose?
|
| Aside: is there a way around IEEE paywall? I'd really love to
| read some of these papers
| wisty wrote:
| Reminds me of the HB100 teardown, but at least this one has an IC
| to make it more soothing that I don't really understand how it
| all works. https://www.allaboutcircuits.com/news/teardown-
| tuesday-hb100...
| metadat wrote:
| Too fantastic not to submit:
| https://news.ycombinator.com/item?id=40834960
| transpute wrote:
| I don't know who designed this, but they were a master of the
| black art of Radio Frequency waveguide engineering. I am
| impressed. The PCB, itself, is a major component. Not only for
| the patch antennas but also several RF filters, the local
| oscillator, and the mixer are all largely made from peculiarly-
| shaped PCB tracks. Apart from the PCB, there are only five
| "components" on the board. Five passive components to implement
| a Doppler radar module. C'mon. You have to be impressed by
| that!
| boguscoder wrote:
| MCU rp2040 from Pi Pico also costs 1$. We really are in great
| time for affordable hacking
| amelius wrote:
| Now if only the GHz-range oscilloscopes came down in price ...
| mastax wrote:
| The competition between Siglent Rigol and Uni-T will most
| likely drive down the cost. From a high baseline but still.
| robertclaus wrote:
| I've played with these all the time! Great to know how they work!
| zer00eyz wrote:
| USB C mm wave "radars" that hook to home automation are a thing.
|
| 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).
| stavros wrote:
| The actual component costs about $5, if you want to roll your
| own with an ESP32.
| mrcsharp wrote:
| The LD2410 (B) is another option and it operates over UART. It is
| a bit more expensive ~$5 but has more configuration options.
| stavros wrote:
| Get the B variant, you can configure it over Bluetooth from
| your phone. Otherwise it's a huge hassle.
|
| That said, it doesn't work very well for me when sitting still
| 4-5m away, it thinks I've left.
| amelius wrote:
| These radars are designed to detect motion, not someone
| sitting still.
| mianos wrote:
| Wrong, most of these radars are 24Ghz and specifically
| designed to detect body micro movements. They specifically
| give both human 'occupancy' and dynamic ranging
| information.
|
| 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.
|
| https://github.com/mianos/hk-heltec-radar/tree/main/src
| stavros wrote:
| This sounds very interesting, how do your drivers work?
| I'd love to try them out, but there's no documentation.
| I've made a sensor board with various sensors, I could
| really use some occupancy detection improvements on the
| LD2450B.
| mianos wrote:
| All the boards provided by HiLink have an on board MCU
| and offer a serial protocol of some sort. I wrote a
| finite state machine based decoder for each them from the
| basic info on some documents,random example code and the
| textual description of the protocol from the aliexpress
| page. They are all wrapped in an outer state machine that
| provides entry and exit triggers. If you can read C++ the
| code is nothing fancy.
|
| 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.
| stavros wrote:
| That's great, I'll have a look, thank you!
| 037 wrote:
| A little tangential, but are these things safe for humans? I have
| a couple of LD2410 devices and I'd like to use one of them with
| ESPHome in the bedroom. I did some research and they seem to be
| very low power and safe, but you know, before sleeping with a
| radar pointing at us all night long, I'm looking for as much
| feedback as possible.
| 05 wrote:
| Some phones have a SAR of almost 2W/kg, compared to that
| milliwatts of 10GHz RF are nothing. Not to mention that with
| standard energy dissipation formula of E~R^(-2) you're getting
| into microwatts at any practical distance from the antenna.
| t0mas88 wrote:
| I have these all around the house, but not in the bedrooms. I
| use weight sensors to detect that someone is in bed and
| traditional PIR for motion in bedrooms.
|
| 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.
| 037 wrote:
| I agree with you, especially regarding children and anyone
| who hasn't explicitly made this choice, which is why I asked
| the question. The only thing is, I suspect we get scared by
| certain words, like "radar" and "microwaves", and then we
| might spend all day with our heads next to a Wi-Fi router or
| a phone constantly downloading files on 4G.
|
| 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.
| Avamander wrote:
| > Probably overly careful, but I didn't want to point a radar
| at my sleeping kids (and myself) for 12 hours per day.
|
| 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."
| davidwritesbugs wrote:
| Loud toys are definitely dangerous for my children, they
| make me angry.
| moffkalast wrote:
| Yeah on one hand you have people afraid of wifi and
| simultaneously sending their kids to play all day outside
| in UV index 11 without a hat or sunscreen. Things that are
| "natural" being inherently safe and anything technological
| literally death itself.
| perlgeek wrote:
| Non-ionizing radio waves are generally safe for humans.
|
| 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.
| lpcvoid wrote:
| >soldiers keeping themselves warm by stepping in front of a
| radar emitter
|
| Holy, did people actually do this? A quick search yielded no
| results. Not sure if thankful or not.
| simondanerd wrote:
| Works, it's a weird feeling, speaking from experience. HF
| antennas can give some respectable burns too.
|
| But the effects are debated and not entirely scientific: ht
| tps://www.reddit.com/r/army/comments/13r6hod/i_keep_being_.
| ..
| moffkalast wrote:
| Weren't microwave ovens invented because someone's
| chocolate melted in their pocket while operating a radio
| transmitter? Maybe it's just a lady godiva story since it
| seems weird that the person wouldn't feel overly hot as
| well, but maybe.
| marcosdumay wrote:
| It's a well known story, he was doing maintenance:
|
| 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.
| moffkalast wrote:
| Oh wow it's even known what brand of a bar it was, funny
| that.
|
| > 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.
| wyager wrote:
| > The only mechanism besides ionization that could harm
| humans [is heat]
|
| 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.
| hippich wrote:
| Almost not related, but reminded me about recent RC hack I was
| working on.
|
| 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.
| aeonik wrote:
| I need to see a picture, but fyi some of components of an
| antenna are "electrically" disconnected, but still play a role,
| wave guides being one example.
|
| 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)
| hippich wrote:
| Just to clarify - I changed transmitters antenna.
| perlgeek wrote:
| Since the user manual for this sensor mentions security
| monitoring as a possible application, I'm wondering: is there any
| simple way to prevent detection from such a mm wave radar?
| (Assuming for simplicity that we know where it's mounted, and in
| which direction it's pointing).
| lindboe wrote:
| Depends on the definition of "simple", imo. The first thing
| that comes to mind is research into materials with good (tens
| of dB), wideband absorption in the mmWave bands. It's an area
| of active research [1] [2] (just a couple articles from a quick
| google, so caveat emptor).
|
| [1] https://www.cambridge.org/core/journals/international-
| journa...
|
| [2]
| https://pubs.rsc.org/en/content/articlelanding/2022/tc/d1tc0...
| Havoc wrote:
| LD2410 work well too (do by the cable too, they have tiny non-
| standard pins)
| farceSpherule wrote:
| You cannot try to rationalize the prices that China charges for
| goods. Everything is, more or less, state-owned and state-
| controlled.
|
| 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.
| marcinzm wrote:
| Isn't the US basically the same? The US government gives
| massive subsidies, tax breaks or just has the military buy
| components for 10x the price (to offset commercial loses and
| R&D).
| ein0p wrote:
| And creates regulatory capture for the rest, e.g. healthcare
| and big pharma ($4T a year), both of which too charge
| nontrivial multiples of what the rest of the world pays.
| What2159 wrote:
| You make China sound like a VC,
|
| Uber, AirBNB, etc ran at a loss to try to own the market.
| dclowd9901 wrote:
| The government also stands to benefit greatly if they throw
| their weight behind smart ideas, just like VCs. It would be
| interesting if the government could fund itself with
| investment.
| marcinzm wrote:
| VC returns are overall much worse than the S&P 500. The top
| firms are potentially better but that's a very limited
| investment pool. Softbank has shown what happens if you try
| the VC approach with a massive pool. Not good returns. The
| core value of VC has historically been due to it being
| uncorrelated with the stock market. That allows it to be a
| risk hedge for investors. The perception is that it is no
| longer uncorrelated so even that value is mostly gone.
|
| 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.
| Aurornis wrote:
| The BOM of this circuit really is very minimal because it's a
| clever circuit.
|
| 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.
| m3047 wrote:
| Wiener functions. I love 'em. An analog application too, top
| secret in WW II. Now also used in handset to eNodeB comms.
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