
Designing a Wireless Device That Lives Forever - adunk
http://www.thingsquare.com/blog/articles/solar-power/
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TeMPOraL
For values of forever equal to ~5-10 years?

I'm not criticizing the article, which is pretty solid, but covers only the
power harvesting topic. I'm just commenting on the title ("Designing a
Wireless Device That Lives Forever").

I would very much like to see a serious discussion about making electronics
live decades. The primary concern would be internal degradation and
environmental damages. How to make batteries that last 100 years? How to make
solar panels that last so long? How to deal with the fact that today's
electronic components are _purposefully_ not designed to last long? That after
many years, your uC will likely just give up and die?

~~~
HeyLaughingBoy
_today 's electronic components are purposefully not designed to last long_

Well, how long do you want them to last? These things aren't designed in a
vacuum, you know. If the customer is willing to pay for a CPU that will run
reliably for 50 years, someone will produce it. However, given that most
consumer electronics are considered disposable, don't be surprised that the
components that go into them aren't designed to last very long.

Engineers -- good engineers, that is -- design to Requirements. If the
requirement is that something last for 15 years and the Reliability engineers
can predict lifespan to +/\- 10% accurately, then a good manager will say
"make sure it lasts at least 18 years." That ensures a 10% margin beyond what
Reliability predicts and it makes sure you don't waste time building a gold-
plated product that costs more than people are willing to pay.

~~~
TeMPOraL
Well, I agree. Note that I didn't _criticize_ that fact here. However, I very
much dislike the disposability of current products, because this is a harmful
way of ensuring repeat purchases through perpetuating waste.

> _don 't be surprised that the components that go into them aren't designed
> to last very long_

It's not surprising, but it's also not _obvious_ that discrete electrical
components like ICs can degrade with use over the span of the years. That's
why I mentioned it.

> _If the customer is willing to pay for a CPU that will run reliably for 50
> years, someone will produce it._

It is a chicken-and-egg problem. No one will pay for such CPU because it costs
a lot, and it costs a lot because no one will pay for it for competition and
economies of scale to kick in...

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jcun4128
Do you need a gateway to access the internet. I understand the problem of FCC,
don't want to use the wrong frequency, but it seems even if your device can
live forever it depends on an existinng network.

When I think of wireless communication in the wild I would have to buy a GSM
module and subscribe to at least an SMS service.

Is there such a thing as free communication that isn't regulated. Maybe that's
what Walkie Talkies are but assuming "internet like purpose" or at least
remote in/out.

That would be cool though just connect to it assuming your device could
interface with it (spread spectrum?)

I think I saw something about phones being able to make their own local
networks as they're able to transmit like up to a mile. It was I think related
to apple phones.

Edit: to try to clarify what I mean by gateway, to connect to the internet
need an ISP, not talking about the TCP protocol but literally have to "be
allowed" to communicate. I know sounding like a conspiracy person I don't know
how to explain it. Also I understand towers transmot far, intercontinental
cable,satellites not saying to replace that.

~~~
retSava
You need a gateway more or less since the devices don't use the same physical
means of communication as the other ones on the network. The mesh network
devices in this post use a 802.15.4-compatible radio, which doesn't work with
wi-fi on a physical layer, so the gateway translates this (and IPv4 <-> IPv6).

All RF communication is regulated (broadly speaking). On the relevant freq.
bands here, the ISM bands on 868/915 and 2.4 GHz, the bands are unlicensed
(you don't need a license) but you have to comply with certain rules. You must
not send too strong, or too much, or occupy too wide freq. band. You must be
able to cope with other transmitters.

Re phones and connections, I think what you mean is ad hoc mesh networks using
the wi-fi that the phones (and laptops) have built in. Then you get a network
in which the devices can communicate with each other (share files,
messages,etc), where they otherwise might have required internet to reach
eachother. It's a different (but interesting) thing...

~~~
jcun4128
Thanks a lot for the information. I had a relevant experience with regard to
video piloting you are supposed to get an Amateur Ham license and then not
transmit (supposedly) more than 25mW but many of the transmitters are close to
1W if not more and depends on antenna design like helical.

Anyway lots of information here thanks.

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luma
Another issue with solar charging in colder climates is snow accumulation on
the panel. Combined with less overall incident sunlight due to shorter days
and cloud cover, charging issues with lithium batteries at temps below 0C, and
the fact that most common air quality sensors of interest (PM) are
comparatively power hungry, it makes fielding a "Lives Forever" device here in
Michigan something of a challenge.

The traditional approach here is large panels with large lead-acid batteries
but the size of the devices involved bring with them further challenges with
siting and maintenance.

~~~
retSava
And dust/sand in eg desert-close environments too!

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retSava
Hi! I'm Marcus at Thingsquare, excited to see this post hit HN :) Feel free to
ask me anything, or hit me up at marcus@thingsquare.com if that suits you
better.

Best, Marcus

------
SlowBro
Useful article! There's one thing you didn't consider: Charging temperature.
Lithium charging temps are typically 0 degrees Centigrade. Any lower could
damage the cells. NiCd is a bit better and there are some low temp NiMh but
for the ultimate go with lead acid. They are not small but there are cells the
size of a D battery.

~~~
retSava
Thanks! You are correct, the li-poly I've looked at specify basically the same
operating temperatures,

discharge: -20 to +60 deg C charge: 0 to +40 deg C

Exactly, the energy density is much less with lead acid, and they also have
poor low-temperature discharge performance. I wonder at what level a very
insulated and slightly heated (if temp < 0) li-poly would be better? I see
there is still room for improvement in the system model we've used in the
article :)

Stay tuned for the sequel! We plan on doing one on indoor-solar powered
devices too :)

~~~
SlowBro
Since charge time occurs during the middle of the day when both ambient
temperatures are higher, and sunlight is warming the enclosure, and since
charging slightly warms cells, and since electronics also warm cells, you have
a better chance of reaching the minimum low charge temperature. Maybe add some
aerogel insulation? Also, active heating could work; requires a larger panel
though.

This solar-powered Pi project integrates a battery heater:
[https://hackaday.io/project/13260-lifepo4weredsolar1](https://hackaday.io/project/13260-lifepo4weredsolar1)

------
SlowBro
Also consider not doing mesh if you need a longer life. I would expect that
LoRa modules could cover the same distance a mesh could, and would only
transmit then power down. Some receiving would be done as well but not as much
as a mesh. By contrast a mesh node is listening and transmitting quite often.

~~~
retSava
Yes, a transmit-only approach would be the most power-saving approach here,
but you'd lose the ability to adjust configuration on-the-fly, and firmware
updates over the air (FOTA), among other things. LoRa has excellent long-range
properties thanks to sub-GHz, modulation, and low bit-rate, but you can just
barely send something back to it and certainly not FOTA it.

The device used in the example post (and here:
[http://www.thingsquare.com/blog/articles/sensortag-
power/](http://www.thingsquare.com/blog/articles/sensortag-power/) ) doesn't
route even if part of a mesh. Ie, it's powered down for the most part so won't
route packets for others, but it can still be many hops away from the gateway.

~~~
SlowBro
Things Network describes a method of updating LoRa device firmwares:
[https://www.thethingsnetwork.org/article/firmware-updates-
ov...](https://www.thethingsnetwork.org/article/firmware-updates-over-low-
power-wide-area-networks)

