Page 344 - Hacking Roomba

Chapter 14 — Putting Linux on Roomba 325

Listing 14-6 Continued

root@OpenWrt:~# ./roombacmd.mpl /dev/usb/tts/0 spinright ; i
sleep 1
root@OpenWrt:~# ./roombacmd.mpl /dev/usb/tts/0 forward ; i
sleep 5
root@OpenWrt:~# ./roombacmd.mpl /dev/usb/tts/0 spinright ; i
sleep 1
root@OpenWrt:~# ./roombacmd.mpl /dev/usb/tts/0 forward ; i
sleep 5
root@OpenWrt:~# ./roombacmd.mpl /dev/usb/tts/0 spinright ; i
sleep 1
root@OpenWrt:~# ./roombacmd.mpl /dev/usb/tts/0 forward ; i
sleep 5
root@OpenWrt:~# ./roombacmd.mpl /dev/usb/tts/0 stop

Making It All Truly Wireless

Until now you’ve been powering the WL-HDD from its AC adapter. That’s fine for debug-
ging, but the point is to make the WL-HDD completely stand-alone and mobile on top of the
Roomba. So the next step is to figure out how to power the WL-HDD.
Asus products usually ship with a high-quality switching power supply that outputs a regulated
+5 VDC instead of the heavy bulky wall warts shipped with most consumer electronics and
which put out a noisy and only approximate +12 VDC. The advantage of the bulky wall wart
to the hacker is that there must be voltage regulator inside the device and the device can take a
wide range of input power. This is not so for the WL-HDD, so you have to construct an exter-
nal voltage regulator to power it off the Roomba voltage of +16V.

Battery Pack Instead of Roomba

The WL-HDD is a pretty useful device by itself. Instead of tying it to Roomba power, you
could instead make a battery pack and then you could stick the WL-HDD up to whatever you
wanted. Imagine making your own network access point and file server at a café without need-
ing any wires at all. Instead of using the +16V supply from Roomba, you can create a supply
using just enough batteries to make a voltage regulator work. The 7805 needs at least 6V in
order to regulate down to 5V. The nominal voltage across AA cells is between 1.2 and 1.5V. Six
cells makes 7.29V, so that’s about optimal. Any more and you’d just be causing the 7805 to
work harder regulating a higher voltage down.
Figure 14-10 shows a battery pack circuit for the WL-HDD. SparkFun sells some 2700 mAh
NiMH AA cells for $2 apiece.This is an amazing amount of capacity in an AA battery. Normal
NiCd rechargable AA cells only put out at most 1000 mAh, so this is about a three-times
improvement in capacity. SparkFun also sells a good but inexpensive charger for the batteries.