Page 292 - Hacking Roomba

Chapter 13 — Giving Roomba a New Brain and Senses 273

Making a Robot Roach

The many competing behavioral drives of a subsumption architecture robot are discussed in
Chapter 1. The BumpTurn program already exhibits a few simple behaviors, but why not add
an appropriate behavior in honor of the bugs that inspired the subsumption architecture idea?
Most insects are sensitive to light in some way.The moth flies toward light, while the cockroach
runs from it. Since Roomba can’t fly (yet), maybe it can be made to act more like a roach. Having
a robot that runs away from bright lights and scurries to the dimmest corner of the room is not
only a great example of real working artificial intelligence, but is also comical to watch.

Figure 13-10 shows the schematic of an updated Roomba BS2 interface. The additions are
photocells. Photocells are light sensitive resistors. Standard cheap photocells (even available at
Radio Shack), range from 50 Ohms in very bright light to 500 kOhms in darkness. These val-
ues vary greatly and are not calibrated. But with such a wide dynamic range, it’s at least easy to
tell bright from dark. Figure 13-11 shows the circuit implemented on the Board of Education.
Notice how each photocell is pointing in a different direction. The one pointing toward the
RS-232 port will be the front sensor and the other the back sensor. With two sensors you can
tell which direction the bright light is coming from.

Vin
1 24
SOUT VIN
2 23
SIN VSS
3 22
ATN RES
4 21
GND VDD
5 20 Vss
R5 6 P0 P15 19
220 R4 7 P1 P14 18
P2
P13
220 8 P3 P12 17
9 16
P4 P11
10 15
P5 P10 14
Photocell R2 0.1 Photocell R3 0.1 R1 12 P6 P9 13 8 mini-din 8pin
11
C1
C2
P8
P7
220
µF
µF
LED1 DD Vss 7 6 5
TXD
4
RXD 3
Vss Vss Vss 2
Vin +16VDC 1
X1
FIGURE 13-10: Adding light sensors for the RoombaRoach
Figure 13-12 shows the Board of Education plugged into Roomba and positioned correctly for
the front and back orientation of the photocells. To anchor the Board of Education and keep it
from sliding around, you can attach a little bit of Velcro between the Board of Education and
Roomba.