[TriEmbed] wireless communications and battery life

[Dewey Hylton]

Hello, first post to the list. I'm somewhat new to the embedded space, having
leveraged rpi/beaglebone type hardware for 1-wire projects and such. But I am
just starting to look at lower power devices such as omega2 and arduino.

Quick introduction, and not so quick questions for those with experience ...

Several decades ago I was an advanced electronics tech in the US Navy, trained
to troubleshoot/repair nuclear instrumentation and control circuitry. Yup, I
was a subsurface "nuke" and operated the reactor plant on 3 different classes
of submarine ... I was no stranger to the soldering iron and could build a
basic calculator from simple components (no chips).

But that was a long time ago, and my only real experience with soldering on
digital equipment is mostly limited to doing so on my Commodore 64 computer
and peripherals. Also not exactly a recent thing.

Now that I have a 13-year-old boy expressing interest in these things, I plan
to get into the embedded stuff so we can work on some neat (and safe!) projects
together. One idea we came up with was a (USPS) mailbox monitor. I have since
found others doing the same thing online, but we have questions and I figured
this might be a good place to ask ...

The original intent was to monitor the mailbox. Could use a physical switch
to determine when the door was opened/closed, or even a light sensor to do
the same. But we wanted to wait a number of seconds after the event, take a
picture of the inside of the box, and send the results via email or mms or
whatever. So not only a fun project for us, but something actually useful in
that we could tell whether a package was present or just more bills. :)

Two basic questions, really. The first has to do with power and battery life,
and the second having to do with wireless communications. 

We started with the Onion Omega2 because (1) very user friendly, as it runs
linux and I can use my python/shell/whatever prowess to get things done. And
(2) it has built-in wifi. We are comfortable with this and have done a few neat
things inside the house. BUT ... I think it's going to be quite power hungry
and may rule it out as far as locating in the mailbox and not having to change
batteries every day or two.

About the wireless bit ... I have plenty of experience with "standard" ip
based networking and wifi, but wonder if that is the best fit here. For starters
my mailbox is about 250 feet from the house. And I figure anything capable of
doing an ip stack over wifi may present similar battery problems. So I am
starting to look into other communications which are not ip based as well.

We recently had our home alarm system upgraded to include wireless sensors.
I learned that not only are these devices able to communicate over fairly long
distances (and through walls/brick/etc.) but their tiny little batteries can
last 3-5 years even with the sensors having a mostly constant connection to the
system. Learning this gave me hope that the mailbox monitor might actually be
feasible.

I have found some wireless modules used to communicate between arduino units;
perhaps the mailbox unit can communicate with a much closer unit, and the closer
unit can be fed power from the house and do the smarter stuff while the remote
unit essentially stays asleep until triggered by light or physical switch in
order to conserve battery.

So ... first steps first ... do any of you have experience with low power
wireless communication which might actually work in my case? Both the distance
and battery life are the main worries currently.

If you've made it this far, thanks for your attention and consideration. I look
forward to hearing some opinions and experiences in this space, and using your
input for projects with my son.

Dewey Hylton