Page 203 - Robots Androids and Animatrons : 12 Incredible Projects You Can Build

a robot with two processors that operate in tandem (distributed
processing).
I will assign the targeting of the light source and bumper switch
detection to one microcontroller, called microcontroller 1. Con-
trolling the steering and drive motor will be assigned to the second
microcontroller, called microcontroller 2. To make this scheme
work, it is necessary to have the microcontrollers communicate with
one another. However, bidirectional communication isn’t required;
we will have one microcontroller talk and the other one listen.

Microcontroller 1 Microcontroller 1 will handle reading the CdS
cells and bumper switch detection. It will communicate to micro-
controller 2 using three I/O lines.
I/O line 1 will communicate the status of CdS 1. If light falling
on CdS 1 is brighter than light falling on CdS 2, then bring the
line low. If equal, bring the line high.
I/O line 2 will communicate the status of CdS 2. If light falling
on CdS 2 is brighter than light falling on CdS 1, then bring the
I/O line low. If equal, bring the line high.
I/O line 3 will communicate either the status of the bumper
switch or that the CdS cells are receiving too much light. In
182 either case this will bring line 3 high.

Microcontroller 2 Microcontroller 2 will check the status of the
three I/O lines and, based on the status, it will steer and move the
robot as follows:

CdS 1 CdS 2 Tilt switch
Line 1 Line 2 Line 3 Results
0 0 0 Sleep mode, not moving
1 1 0 Move forward
1 0 0 Steer right, move forward
0 1 0 Steer left, move forward
X X 1 Avoid mode
X don’t care.

Accordingly, lines 1 and 2 represent the two CdS cells and line 3,
the status of the bump switch.
Adding sleep mode
I added a sleep mode for when the ambient light is very low. The
robot moves forward when both CdS sensors receive approximately
the same light intensity. The robot steers right or left when one CdS

Team LRN
Chapter eight