When I got my first Indiglo watch, I realized the backlight had such fast rise/fall times (as compared to its incandescent predecessors) that it could be used to transmit data. I imagined watches with photocells, held face-to-face, flickering their backlights at each other to "synchronize watches" before a special-ops mission or something.
A few years later, Timex DataLink came out, indeed using a photocell to receive data, but not using the backlight to transmit it! And in all the years since, nobody ever took advantage of that.
But here we seem to be, with phones, a million times more powerful and a million times less power-efficient.
It is deeply wild that the “hello world” project of arduino like systems is to on-off modulate a ~500 THz electromagnetic wave emiter. (Aka blinking an led)
Also that if you want to emit in the mhz range you need permissions and specialist equipment, but in the ~500 THz range you can just use a sub-dolar part and go ham with it without needing to be a ham.
It's high time that we start regulating terahertz EMF radiation. It is dangerous stuff. It can even cause physical eye damage! Scientists refer to it as "pollution" when it occurs at night, because it's so unnatural for the human body to be exposed to so much of it after dark.
The fact that THz EMR is completely unregulated and never discussed by the media is a sign that politicians and the scientific community are complicit in protecting industry at the expense of people's health.
or a design firm that accidentally reinvented the remote control.
if they built a protocol around it that handles error correction and noisy/intermittent links as well as nice apis for both sides, then i'd say they have something interesting.
1.5 kb/s at 5 cm is rather bad. Assuming 24fps (typical smartphone camera) sample rate with QAM-256 modulation, shouldn't the bandwidth be at least a magnitude higher even after error correction? They have 16 LEDs, assuming half are fiducial markers, they will have 8 extra channels.
Where are you seeing 16 LEDs? Everything on the site seems to suggest it's a single LED. I'm not sure how you reach 1.5kbps with a single LED on a wide range of phones.
With the rolling shutter of smartphones, combined with the fact the light from the led will spread slightly throughout the frame (dirt in the lens etc), you effectively get one piece of information per row of the image. So a 1080p60 video, which most phones are capable of, gives you 64kbps.
With no feedback channel though, one can't characterize the channel though, so you need to have super large margins to be sure it's going to work.
> IrDA was popular on PDAs, laptops and some desktops from the late 1990s through the early 2000s. However, it has been displaced by other wireless technologies such as Wi-Fi and Bluetooth, favored because they don't need a direct line of sight and can therefore support hardware like mice and keyboards. It is still used in some environments where interference makes radio-based wireless technologies unusable.
> An attempt was made to revive IrDA around 2005[3] with IrSimple protocols by providing sub-1-second transfers of pictures between cell phones, printers, and display devices. IrDA hardware was still less expensive and didn't share the same security problems encountered with wireless technologies such as Bluetooth. For example, some Pentax DSLRs (K-x, K-r) incorporated IrSimple for image transfer and gaming.[4]
Irda was most definitely available on phones. It was possible to get a laptop online by correctly aligning it and a phone on a desktop. Also very commonly used by printers
Man I miss having a handheld with IrDA on it. I had every device in my house programmed into my Palm. TV, VCR, air conditioner, DVD player, stereo. Not to mention all the universal remote apps that'd let you change the channel and volume in bars, restaurants, and waiting rooms.
Problem is that IR blasters can't receive, so you cant copy the signal from the original remote. Finding the codes online can be very hit or miss, for example I never did find one for my AC during the four years I had a phone with an IR blaster.
Same here on desktop Chrome. I think its a poor execution of Tesla site. Moment I touch the wheel it takes me to next slide... that is - split on the screen with the previous one. Nightmare.
Low bandwidth could be a feature. You'd know that your winking product can't be sending a whole lot of information about you that way. Or at least it would take a while to do so.
An audio version of this sort of thing was Chirp. I wrote the original
audio code to implement something that sounded aesthetically pleasing
like a bird twitter, but actually used multi-carrier FM plus error
correction and a whole bunch of stuff to be a "constellation" modem. I
believe the company are still going. IIRC, when I left they'd got to
the point of realising that in a noisy environment, even with echo
cancellation, you couldn't really do serious data transfer - and why
would you if you have Bluetooth anyway.
The real application for these "last meter" contactless ideas that use
stalwart built-in transducers like mic+speaker or LED+camera, are to
send short codes, such as shortened URLs. There's a whole bunch of fun
to had using them for surreptitious advertising and public
steganography.
This can probably be sabotaged quite easily by putting a powerful enough near-visible light LED somewhere else in the room and a high-res camera to record responses. Many phones have trouble filtering out some IR (you can test this by aiming a remote at your phone with the camera app open, mine shows IR as pink light) and I don't expect communication lights to be too bright because of the discomfort that comes with flashing.
I also think this tech is entirely impractical for one single reason: flashing visible lights can easily induce seizures.
With BLE available in pretty much every OS (and even in many browsers), I don't see the added value of quickly flashing a smartphone flash light.
34 comments
[ 3.2 ms ] story [ 76.0 ms ] threadWhen I got my first Indiglo watch, I realized the backlight had such fast rise/fall times (as compared to its incandescent predecessors) that it could be used to transmit data. I imagined watches with photocells, held face-to-face, flickering their backlights at each other to "synchronize watches" before a special-ops mission or something.
A few years later, Timex DataLink came out, indeed using a photocell to receive data, but not using the backlight to transmit it! And in all the years since, nobody ever took advantage of that.
But here we seem to be, with phones, a million times more powerful and a million times less power-efficient.
Yikes.
Double yikes.
triple!
Also that if you want to emit in the mhz range you need permissions and specialist equipment, but in the ~500 THz range you can just use a sub-dolar part and go ham with it without needing to be a ham.
The fact that THz EMR is completely unregulated and never discussed by the media is a sign that politicians and the scientific community are complicit in protecting industry at the expense of people's health.
if they built a protocol around it that handles error correction and noisy/intermittent links as well as nice apis for both sides, then i'd say they have something interesting.
Or does the amplitude of the led vary continuously? I was assuming PCM.
With no feedback channel though, one can't characterize the channel though, so you need to have super large margins to be sure it's going to work.
> IrDA was popular on PDAs, laptops and some desktops from the late 1990s through the early 2000s. However, it has been displaced by other wireless technologies such as Wi-Fi and Bluetooth, favored because they don't need a direct line of sight and can therefore support hardware like mice and keyboards. It is still used in some environments where interference makes radio-based wireless technologies unusable.
> An attempt was made to revive IrDA around 2005[3] with IrSimple protocols by providing sub-1-second transfers of pictures between cell phones, printers, and display devices. IrDA hardware was still less expensive and didn't share the same security problems encountered with wireless technologies such as Bluetooth. For example, some Pentax DSLRs (K-x, K-r) incorporated IrSimple for image transfer and gaming.[4]
https://studios.disneyresearch.com/2012/12/03/an-led-to-led-...
https://la.disneyresearch.com/publication/connecting-network...
The real application for these "last meter" contactless ideas that use stalwart built-in transducers like mic+speaker or LED+camera, are to send short codes, such as shortened URLs. There's a whole bunch of fun to had using them for surreptitious advertising and public steganography.
I also think this tech is entirely impractical for one single reason: flashing visible lights can easily induce seizures.
With BLE available in pretty much every OS (and even in many browsers), I don't see the added value of quickly flashing a smartphone flash light.
https://www.youtube.com/watch?v=O3Pf4TZ_vOE
https://github.com/gioblu/PJON/tree/master/src/strategies/An...
http://mecrisp.sourceforge.net/ledcomm.htm
https://hackaday.com/2019/12/22/optical-communication-using-...