Page 347 - Hacking Roomba

328 Part III — More Complex Interfacing

In Figure 14-13, the lead from the battery is split and run through an ammeter (a multi-
meter configured to measure current) to check how much current the WL-HDD actually
draws from the batteries. It draws about 450 mA, with slight fluctuations based on CPU
usage. With the 2700 mAh batteries, you should get about 2700 / 450 = 6 hours from a
fully-charged battery pack. That’s about three times longer than Roomba lasts on its
battery pack.

FIGURE 14-13: Testing current draw of the WL-HDD

WL-HDD on the Go

If you would like to use the WL-HDD without Roomba, you can easily lash together the
battery pack to the WL-HDD and take it anywhere you want. Figure 14-14 shows how you
could do it with a long piece of Velcro. The resulting bundle fits pretty easily in a book bag.
A better enclosure could make an even smaller bundle. Insert the power plug to start up and
pull it out to power down. Unlike most OSes, OpenWrt is very tolerant of sudden power
removal.