Inside a $1 radar motion sensor • Hacker News Board

Re: Inside a $1 radar motion sensor

#71

Post by wyager » Sun, Jun 30, 2024, 3:22 PM UTC

perlgeek wrote: post #52

037 wrote: post #15

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.

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 d…

> 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.

Re: Inside a $1 radar motion sensor

#72

Post by marcosdumay » Sun, Jun 30, 2024, 3:29 PM UTC

moffkalast wrote: post #64

lpcvoid wrote: post #53

Earlier quoted context omitted.

>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.

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.

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.

Re: Inside a $1 radar motion sensor

#73

Post by nothacking_ » Sun, Jun 30, 2024, 3:48 PM UTC

tstrimple wrote: post #16

silisili wrote: post #13

Earlier quoted context omitted.

I think you could go cheaper. A sound detection sensor is a bit cheaper, and it just needs to detect the word 'vegan.'

Strangely enough I've heard far more people make this "joke" than actual vegans speaking up. Even when living in LA.

That's the trick, you invert the logic. If you hear the word vegan, assume the person saying it is not.

Re: Inside a $1 radar motion sensor

#74

Post by 01100011 » Sun, Jun 30, 2024, 3:59 PM UTC

tstrimple wrote: post #16

silisili wrote: post #13

Earlier quoted context omitted.

I think you could go cheaper. A sound detection sensor is a bit cheaper, and it just needs to detect the word 'vegan.'

Strangely enough I've heard far more people make this "joke" than actual vegans speaking up. Even when living in LA.

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).

Re: Inside a $1 radar motion sensor

#75

Post by swsieber » Sun, Jun 30, 2024, 4:00 PM UTC

stavros wrote: post #50

victorbjorklund wrote: post #49

Earlier quoted context omitted.

A hack is to put a sensor on the chair

Hmmmmm that's not a bad idea, I'll have to see how to do that, though. I don't want cables restricting me.

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.

Re: Inside a $1 radar motion sensor

#76

Post by stavros » Sun, Jun 30, 2024, 4:03 PM UTC

swsieber wrote: post #75

stavros wrote: post #50

Earlier quoted context omitted.

Hmmmmm that's not a bad idea, I'll have to see how to do that, though. I don't want cables restricting me.

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.

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...

Re: Inside a $1 radar motion sensor

#77

Post by farceSpherule » Sun, Jun 30, 2024, 4:30 PM UTC

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.

Re: Inside a $1 radar motion sensor

#78

Post by marcinzm » Sun, Jun 30, 2024, 4:34 PM UTC

farceSpherule wrote: post #77

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.

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).

Re: Inside a $1 radar motion sensor

#79

Post by What2159 » Sun, Jun 30, 2024, 4:45 PM UTC

farceSpherule wrote: post #77

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.

You make China sound like a VC,

Uber, AirBNB, etc ran at a loss to try to own the market.

Re: Inside a $1 radar motion sensor

#80

Post by dclowd9901 » Sun, Jun 30, 2024, 4:53 PM UTC

What2159 wrote: post #79

farceSpherule wrote: post #77

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.

You make China sound like a VC, Uber, AirBNB, etc ran at a loss to try to own the market.

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.