Page 130 - Making things move_ DIY mechanisms for inventors, hobbyists, and artists

110 Making Things Move

SparkFun’s PRT-00339 is a polymer lithium-ion battery (LiPo for short). This is currently
the most advanced battery technology with the highest energy density (energy density
= energy / volume).

These batteries also need a special charger, of course, and you can get a simple one at
SparkFun (PRT-08293).

Plug-In Options

The advantage of having a project that doesn’t need to move around is that you can
have a big, heavy power supply, or you can plug right into the wall. The following are
a few ways to turn AC power from the wall into DC power we can use.

Computer Power Supplies
If you’ve ever looked inside a desktop computer, you probably noticed a big, boxy
looking thing, like the one shown in Figure 5-7, that was making some noise. This box
is actually the power supply for the computer, and the noisy thing was probably the
fan inside the power supply used to keep it cool. If you think your computer’s power
comes from the wall socket where you plug it in, you are only partly right. Your
computer wants DC power, not the AC
FIGURE 5-7 A computer ATX power
power from the wall, so this power supply
supply (image used with permission from
does the conversion and has some smarts SparkFun Electronics)
built in that regulate the flow of power and
avoid overloads.

SparkFun sells a computer power supply
(TOL-09539), and you can get the
accompanying ATX connector breakout
board (BOB-09558) to take the mess of
wires coming out of the box and give you
a useful 3.3V, 5V, or 12V DC supply to
power your mechanisms. Both of these
can be had for under $35, so if you have
a power-hungry immobile project, the
combination is a very practical option.