Page 56 - Hacking Roomba

Chapter 2 — Interfacing Basics 37

The remote control codes are undocumented in the ROI specification, but Table 2-4
shows the remote codes for the standard remote. There are 255 possible codes, allowing
for many different possible commands. The more powerful Scheduler remote likely uses
some of them. The RoombaComm code, introduced below and available for download at
http://roombahacking.com/, contains the most comprehensive list of remote codes.

Table 2-4 Remote Control Codes
Value Hexadecimal values Description
255 0xff No button pressed
138 0x8a Power button pressed
137 0x89 Pause button pressed
136 0x88 Clean button pressed
133 0x85 Max button pressed
132 0x84 Spot button pressed
131 0x83 Spin left button pressed
130 0x82 Forward button pressed
129 0x81 Spin left button pressed

Distance and Angle
Roomba computes the distance and angle values by watching its wheels move. This doesn’t
always correspond to actual motion. The two-byte values are combined into a single 16-bit
signed number through the standard method of:
value = (high_byte << 8) | low_byte
Or in plain English: Take the high byte, shift it up 8 bits and overlay (OR) it with the low byte.

Both the distance and angle are cumulative values and are cleared after they are read. This
means that in order to get accurate readings, they must be read often enough that they don’t
overflow. In practice this isn’t that much of a problem. A larger problem with not reading often
enough is the loss of awareness of the true motion. Distance and angle give a single vector
direction from point A to point B. In actuality, Roomba may have moved in a multi-point
zigzag motion (or any other path) between points A and B. In Chapter 6 you’ll delve into the
details of dealing with these issues.
Power Sensors
Figure 2-7 shows the details of the 10 bytes that make up the power systems sensor packet
group. Roomba spends a lot of time thinking about power, and that is reflected in this ROI