Turning off the mesh to save battery power

[John Gilmore]

> hey guys, here in Nepal we are deciding whether or not to turn off the
> mesh on our custom XO build in order to save power. We will leave on
> regular wifi. 
> 
> Any ideas on how much power we will actually save? An extra hour of
> battery life would be worth it

(1) Try it and see, that's probably the easiest way.  Every laptop has
an instrument in the battery that you can measure its power draw with.
See:

  http://wiki.laptop.org/go/XO_power_draw

When I measured it on 2008-09-12, I got about 0.2w difference between 
a WiFi access point and mesh.  It probably matters how busy your mesh
is, since transmitting uses more power than just sitting there waiting
to receive.

(2) The big win in 8.2.0 from turning mesh off is that the entire WiFi
chip can be powered down when the laptop is closed and suspends.  This
stretches the suspend time from about 8 hours to at least 48 hours,
meaning the kids can just close the lid rather than power-off.  Then
the laptop will be instantly available whenever they open it (e.g. at
home).  If the mesh is still on, the WiFi chip needs power to do its
packet-forwarding job.

(3) If you want an extra hour of battery life, work on the screen
dimming algorithm, or teach kids to turn down their brightness to
increase battery life.  Summary from my results: "Normal power
consumption of about 6 watts. By dimming the screen, you can save up
to a watt. By turning the screen all the way off, you can save another
0.5 watt (total 1.5 watts for screen). By turning the WiFi chip off,
you can save up to a watt."

	John