Off-grid fun
------------

Lately cmccabe has been writing[1,2] about his efforts to bulid an
RPi pubnix powered by a gravity battery.  This is super cool!  About
as cool as Tomasino's solar powered wireless free library, which - and
I really should have said this earlier! - is one of the coolest things
I've read in gopherspace.  I'm really interested in off-grid
computing.

I'm long, long overdue for an update on my Franken-Peugeot bicycle
project (shouldn't be too much longer, I promise!).  But one important
change since I last wrote about it is that it's acquired a new front
wheel - with a dynamo hub.  If your idea of a bicycle generator is one
of those little "bottle dynamos" which physically presses up against
the side of the tyre, you may be interested to know that they've come
a long way since then!  Modern dynamos are built right into the wheel
hub (the part in the middle, where the axle passes through).  There's
no additional physical contact involved compared to a standard wheel,
so there is a lot less (but still some) drag, and no wear on the tyre.
High quality dynamo hubs have become pretty popular with serious
cyclotourists, randonneurs and other people who ride long times and
long distances.  Mine is an entry level model by Shimano designed for
city bikes, so nothing fancy.  It puts out 3W at 6V.

The classic application for a generator on a bicycle is, of course,
for lighting.  I fully intend to explore lighting options, but not for
several months: it's only a week until Midsummer's Day here, and it's
light enough to ride from before I ever get out of bed until later
than I'm ever likely to be out.

An increasingly common alternative application of generator hubs is
for charging devices while riding during the day.  Phones, of course,
but also headlamps or flashlights, GPS receivers, radios or
walkie-talkies; anything you might bring on an adventurous ride.  I'm
really interested in this.  I have exhausted my phone's battery on a
ride before after getting lost in the middle of nowhere and making
extensive use of the GPS, and it's not fun.  Being able to charge it
while riding is super appealing.

There are plenty of expensive USB charging devices you can buy for
plugging into dynamo hubs, but I'm excited to try homebrewing my own
solution.  Dyanmos generate AC, so after running the output through a
bridge rectifier I'm going to end up with a DC voltage well above the
5V of USB power.  A lot of people who've built their own chargers seem
happy to use a 7805 linear regulator to drop it down, but I want to
use this as an opportunity to finally get some hands-on experience
with building a switching regulator.  I have a bunch of MC34063 chips
- the Trabie[6] of switching regulators! - that I bought on sale years
ago which I still haven't done anything with, and this seems like a
perfect opportunity to finally change that.  I'm looking forward to
experimenting!

[1] gopher://zaibatsu.circumlunar.space:70/0/~cmccabe/18-off-grid-pubnix-test-01.txt
[2] gopher://zaibatsu.circumlunar.space:70/0/~cmccabe/19-off-grid-pubnix-test-02.txt
[3] gopher://gopher.black:70/1/phlog/20181014-little-free-library-part-1
[4] gopher://gopher.black:70/1/phlog/20190109-little-free-library-part-2
[5] gopher://gopher.black:70/1/phlog/20190115-little-free-library-part-3
[6] gopher://kagu-tsuchi.com:70/0/phlog/worst_car.txt

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