
Smart Watch Will Charge Itself Using Heat from Your Skin - teklaperry
http://spectrum.ieee.org/view-from-the-valley/consumer-electronics/gadgets/this-smart-watch-will-charge-itself-using-the-heat-of-your-skin
======
duskwuff
"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.

~~~
rasz_pl
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.

~~~
devindotcom
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.

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fisherjeff
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?

~~~
david-given
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](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.

~~~
nom
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.

~~~
david-given
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.)

~~~
nickff
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.

~~~
david-given
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...](http://www.atmel.com/products/microcontrollers/arm/sam-l.aspx)

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.

~~~
nickff
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.

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

~~~
hyperpape
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?

~~~
Seebeck
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.

~~~
gnicholas
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?

------
beambot
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...](http://www.travisdeyle.com/blog/2007/03/12/thermo-electric-
generator-energy-scavenging)

~~~
digikata
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](https://en.wikipedia.org/wiki/Eco-Drive)

------
kodis
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.

------
capote
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.

------
ourcat
I love that they're called "Matrix".

Turning us into batteries.

------
simonbarker87
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.

------
drzaiusapelord
>“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.

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gumby
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.

