[Tiny-tux] Meeting notes, Thu 24 Feb 2011

[Wladyslaw Zbikowski]

In attendance: Corey, Wladyslaw, Paul, Miloh, John, Tony, Robert, Zac, Erik

Paul is interested in hacking Canon digital cameras to encrypt
pictures. He is looking at Rockbox and the Canon Hacker Developer Kit.

Miloh brought a number of 8" Insignia devices (Chumbies). One is
destined for Metalab in Austria; at least one is for sale (~$110).

Miloh would like to use a Chumby to drive the Makerbot so people can
produce parts without hooking up a PC.

Corey would like to connect a Chumby to a webcam to build a navigation
or security system.

Corey is also interested in building something for Sparkfun Autonomous
Vehicle Competition, possibly using a Chumby for the autonomous
navigation algorithms and an Arduino for realtime control.

Wladyslaw and Tony discussed building a set-top box running Boxee on
the Gumstix Overo Fire and Tobi expansion board with DVI out. Tony
pointed out that while the Chumby can drive SD video through its
compsite output, it probably doesn't have the horsepower to decode
H.264.

Wladyslaw and Corey are building Ubuntu filesystems for the Gumstix
using rootstock, while complaining bitterly about OpenEmbedded.

Battery Discussion!

There was some discussion of building battery packs for Chumby,
Gumstix, and other boards requiring 5V at 1-2A. Zac suggested a
Lithium Ion cell phone battery at 3.7-4.2V, stepped up to 5 with an
LM2577 DC-DC converter. He recommended against LiPo because they are
prone to puncture. Corey has a source for LiFe (Lithium Ion Phosphate)
cylinder cells for about $3. These have a 18mm x 65mm form factor
(slightly larger than AA) with relatively low energy density. Unlike
other Lithium Ion batteries they do not require a protection board
(~$2) to guard against overcharge and overdischarge, as long as they
are only charged at 3.6V (short of the peak 3.7V).

Zac recommended finding old Bluetooth headsets (2001 or newer) to use
for their Lithium Ion charging circuitry. They have a TI chip for
calibration and charging which normally runs around $20. They can be
used with higher capacity batteries than they were originally intended
for, by just charging for a longer amount of time. Zac advised to
never charge at faster than 700mA.

Tony pointed out that the i.MX233 SoC used in the Infocast 3.5" has
built-in charging circuitry which is configurable in software.

A number of people are interested in building switched-mode battery
power supplies during Monday Circuit Hacking.