Smart Watch Will Charge Itself Using Heat from Your Skin | Hacker News Reader

Smart Watch Will Charge Itself Using Heat from Your Skin

spectrum.ieee.org

28 pointsteklaperry49 comments

"Launched […] on Indiegogo"

This should be a huge red flag.

Indiegogo is notorious for hosting fundraisers for technology projects that are impractical, overpromised, or even physically impossible. Unlike their competitor Kickstarter, Indiegogo performs almost no fact-checking on projects, which has resulted in a number of high-profile scams (like the Skarp laser razor, the DragonFly FutureFon smartphone, and the Triton Gills breathing apparatus).

The fact that their fundraiser is operating in Indiegogo's "flexible funding" mode -- which allows them to receive funds even if their goal is not met -- should be an additional warning sign. Real hardware projects have financial targets that must be reached to make them break even.

but a writeup on ieee.org has to mean they are vetted!

oh wait, its some blog hosted on ieee domain :), certain Australian is bound to make a video about this.

Spectrum is a great publication actually. They cover a lot of stuff fresh out of the lab, but I'm surprised to see this on there. I can't remember the last time I covered something launching on Indiegogo, it always turns on my BS sensor.

Woah, we didn't realize launching on IndieGoGo would be such a red flag. Thank you for the lesson learned.

Please believe me when I say that we are a real company with real facilities, not a scam. Some other things that may help reassure people:

  *Our 8-person team has 5 Ph.D.'s, including our founder who did his graduate work in thermoelectrics. Feel free to Google the rest of the team: http://matrixindustries.com/#team

  *We have funding from Khosla Ventures and 3M, among others

  *We have real prototypes in the lab right now that generate power when you put them on

So if a human burns ~2000 calories per day and has 1.5-2 m^2 of skin, that means that a reasonable upper bound on (mean) thermal flux density of human skin is around 65 W/m^2. So if a watch makes contact with an area of, say, 2 square inches, that comes out to... 85 mW of available thermal energy?

Am I missing something?

To a first approximation that looks fine[1]. To a second approximation one might consider that heat doesn't exit any endotherm in remotely equal surface fashion[2]. And if anything the wrists appear as local minima.

[1] https://en.wikipedia.org/wiki/Spherical_cow

[2] http://i.stack.imgur.com/CsnO5.png

Air and clothing vs a metal plate in skin contact makes that slightly less important. The real probably is you probably get 2% efficiency due to minimal temperature differences involved, and people take their watches off.

you can divide that by ~100, unless you manage to keep temperature difference at 100'

Not a direct response to you, but if you calculate Carnot thermal efficiency with a skin temp of 37 C (likely too high), and ambient temperature of 20 C (probably about right), you get 5.5%.[1] Using this result (combined with yours), the watch has to run on less than 5 mW of electrical energy.

[1] http://calistry.org/calculate/thermalEfficiencyCalculator

P.S. It would also be interesting to see how much waste heat is removed in breathing.

5mW should be enough for a simple e-ink watch. CPU and display have to stay idle most of the time though and you can't communicate a lot over radio. It should be possible, even with that little power if you can accumulate the energy in a capacitor. However it's not an easy task and poses a real engineering challenge, that's for sure.

Many of the Cortex M0s are very good at conserving power, and have a number of low-power and sleep modes, which make running at these levels quite easy. On the other hand, while Bluetooth 4.0 is low-power friendly, cost and size limits inherent to the watch will probably force the team to do a custom antenna and FCC certification, which is expensive, slow, and painful.

I would say the electronics are not too complicated or difficult, but the energy harvesting and design will be tough, and the whole project will be quite arduous.

It would be very interesting to see their development plan, and whether they are going for an iterative/modular design, or all-in.

I agree, the CPU is probably the smallest problem.

I'm curious with how little power you can get away with using a BLE radio. Especially if you constrain yourself to some kind of polling mode where the watch reaches out to the smartphone every minute or 5 minuetes or so.

A basic low-power microprocessor (like the MSP430) will run at 1MIPS at about 0.5mA. (Less when sleeping.) At 3V, that's 1.5mW. A Sharp epaper display, like on the Pebble, consumes basically nil when not changing, although I can't find data on energy use when updating. A traditional STN LCD uses about 1mW.

So I reckon it's plausible, just --- thermoelectric generators have traditionally been really inefficient, and I don't know whether getting 2.5mW of electricity out of 85mW of heat is possible. Particularly if you're like me and wear the watch quite loosely.

Edit: Datasheet: http://www.ti.com/lit/ds/slase54a/slase54a.pdf

That's an FRAM model with non-volatile RAM, so it can power down completely without losing memory. It claims it'll sleep with the clock on at 450nA. (That's nano, not milli.) It also claims it'll run with the processor on at 120 µA/MHz, so the 1 MIPS figure I quoted above must be about 4MHz. I've never run one below that but I gather they'll go down to about 500kHz. Enabling peripherals costs more, of course, but you can leave them powered off until you want to use them.

So, yeah. Totally plausible.

There is no epaper in pebble. You can get ~25 microwatts per cm2 per K temp difference (according to Linear). Enough for the Sharp memory display and simple clock circuit.

Yeah, it's the screen I'm curious about. The renders on their Indiegogo page make the screen look pretty awesome.

FWIW, the original Pebble is rated at 2.8 mW and the Pebble Time is 4.6 mW.

Most smartwatches are also paired with phones. So there's extra power usage for bluetooth, too.

There are CPUs out there with sleep currents well below 0.1 mA, for example the Microchip nanoWatt XLP. The product page advertises 9 nA in a best case sceneario.

Well, the MSP430 sleeps at about 1µA --- below if you turn the clock off!

But as you're not really getting anything done when the processor's not asleep, I quoted the power consumption when running. (Of course it's possible to use a capacitor to soak up energy and then run the processor at higher currents, in burst. You'd probably want to do this if you want radio. But on average, you're still getting about the same amount of work done.)

Slight digression, but the MSP430 is obsolete; modern low power ARM microcontrollers are superior in every dimension.[1]

[1] I have worked on products with both uC, and the company where I work buys both by the reel and tray.

Would those be the new Atmel SAM L21? I see a reference to 35 µA/MHz and 200 nA sleep mode:

http://www.atmel.com/products/microcontrollers/arm/sam-l.asp...

So:

(a) yay! super low power processors! Bet you can run these off a couple of long wires and radio scavanging;

(b) ARMs are so dull. [sad face] The MSP430 is a lovely processor to write machine code for. ARMs are just... dull.

Anyway, thanks for the suggestion. I think the MSP430s have a monopoly on FRAM, which makes a vast difference in usability, but I'll check these out.

The low power Kinetis processor can run at low speed for 32 µA, and down to 1.7 V. Many of the ARM manufacturers produce similar parts.

Interesting. Is it still able to wake up regularly without an external source to trigger the interrupt? Or does it have a timer with a dedicated oscillator / clock for that purpose?

Most modern low-power microcontrollers have low power timers which can be left on with the rest of the processor asleep; this low power timer is usually capable of running very slowly, and generating occasional interrupts to wake the processor.

Wow, so great to see this on the front page of HN! I work here, any questions, just ask!

Just skimmed the article. Do you think this tech can be used to power phones too somehow in near future? I always imagined that in future, devices wouldn't need charging.

Right now, even a low-end smartphone has power requirements that are about an order-of-magnitude too high for that to work, so we would probably need both better thermoelectrics (we're working on that!) and more power-efficient smartphones to close that gap.

The other issue is that since, unlike a watch, you don't "wear" your phone on your skin, we would need a clever approach to collecting body heat, perhaps in concert with some kind of tether.

Don't pockets get pretty warm?

It depends on a temperature gradient. One side has to be warm, the other side has to be cold. If you put it in a pocket it stops generating power.

try 4 orders of magnitude

If you are Seebeck, where are Peltier and Thomson? ;)

This looks exciting! Did you consider solar at all, or were you always a thermoelectric group from the start? What was the thought process behind making a watch as your first product?

We've been a thermoelectric company from day one. We'd like to see thermoelectrics not only in wearbles, but also in smart sensors, medical devices, various IoT devices, etc. The watch just seemed like a good place to start because we would hear about people who would stop wearing them because they forgot to charge them.

Are you confident in generating enough power from the watch body alone, or are you evaluating the strap as a contact point as well?

If it requires temperature differentials so that the cold side of the watch is away from your skin, what happens when the external temperature gets somewhere above 90F/32C?

The technology is able to harness a temperature gradient regardless of its direction, but you're right that the larger the gradient the better it works.

Do you expect to see different performance (and therefore adoption rates) in different regions of the US/world?

Folks in sunny California saw optimal performance of their Tesla batteries, compared to folks in the chilly northeast—perhaps this is the flip side of the coin?

How much power do you actually get out of the TEM?

Also, does the watch charge in any other way? I could imagine using the TEG to top off a normal usb or induction charge. Even if that only doubled the time between charges, that would be a significant improvement.

Does the side of the watch that's against your skin make your skin feel any different (e.g. colder)?

Seiko built similar thermoelectric harvesters for their (very!) limited run of Thermic watches in the late 1990s:

http://www.travisdeyle.com/blog/2007/03/12/thermo-electric-g...

Citizen, Seiko, Casio all seem to offer a wide range of solar powered watches now. I wonder what the ranges are for energy collected by watches for various thermal, kinetic, and solar methods?

I've had a Citizen EcoDrive (solar) for over a decade now.. it just keeps going..

Edit: I see now Citizen also started (1999) and stopped making thermal powered watches... https://en.wikipedia.org/wiki/Eco-Drive

I see the same problem here as with self winding watches -- the idea works well enough so long as a person has only one watch which they wear daily. Otherwise, the watch may lose enough energy that it stops keeping time and has to be reset the next time it's worn.

Watch collectors can buy "watch winders", a motor driven storage case that will keep their self-winding watches going when they're not being worn. I suppose that now the manufacturers will have to add little heating pads to keep these body heat powered watches going as well.

Why don't they just use kinetic energy from the movement of your arm like mechanical watches have been doing for many decades now? Surely it's easier and more of it.

I love that they're called "Matrix".

Turning us into batteries.

Temperature differential is the hardest aspect of this, even if they somehow manage to pipe the heat around the edges any time the user is wearing long sleeves you're going to wreck the heat dissipation - if they could use the top surface of the strap as a heat sink then at least they could get the surface area.

Using a Marlow TEG harvester is out of the question as they are too big (and work best at much higher temperatures) but I guess one of the micro scale TEGs made by Micropelt could maybe possibly work - last I checked they were still in beta and when I referenced them in my lit review 7 years ago they were just getting going so it's been a long slog.

Even then, as others have said, the harvestable energy from the surface of the skin is so small that it would have to be pretty limited in capability. The best bet would probably be an arsenal of energy harvesters, micro-scale vibration energy harvesters (mems piezo maybe), a magnet in a coil to get walking energy and then also TEG. Could land up being pretty huge.

Either way, so long as this isn't a scam, good luck to them.

>“We see ourselves as a thermal energy harvesting company,” Anne Ruminski, Matrix’s head of engineering told me, not a watch company.

Harvesting humans for energy? I guess the Matrix name is fairly tongue-in-cheek here.

Curious to know how plausible this is considering how little heat we produce. I wonder if there's a catch like "needs weekly charging" on top of the heat based charging or also has a charger from the kinetic movement of our wrists with the heat charging being a gimmick to get attention and VC money.

I'm also concerned this watch will have way too many energy saving compromises to be practical. How often will it pool its bluetooth connection for messages? If it all? The indiegogo page doesn't show any integration with your phone other than fitness stuff, which can be synced infrequently. What about alerts and messages? I don't even see that addressed. Sorry, but its not a smartwatch if it can't integrate with my phone for alerts and messages. Its just a fitness device with a clock then.

Pelting devices are pretty expensive and relatively low efficiency. I'm surprised nobody has made a small MEMS oscillator to generate power the same way self-winding mechanical watches work. Perhaps arms smply don't move enough.

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