Page 200 - Robots Androids and Animatrons : 12 Incredible Projects You Can Build

8.13 Close-up photograph detailing front drive wheel, showing coun-
terweight, drive wheel, gearbox motor, and light sensor with shroud

operation as described in Chap. 6 for the light tracker circuit. 179
The operation of the sensor array is shown in Fig. 8.15. When both
sensors are equally illuminated, their respective resistances are
approximately the same. As long as each sensor is within ±10
points of the other, the PIC program will see them as equal and
doesn’t move the servo motor (steering). When either sensor falls
in the shadow of the main light source, the resistance variance
between the sensors increases beyond the ±10-point range. The
PIC microcontroller activates the servo motor to bring both sensors
back under even illumination. In doing so, this steers the robot
straight to the light source. If the sensors detect too great of a light
intensity, the robot will go into avoid mode.
Schematic
The schematic for the robot is shown in Fig. 8.16. Intelligence for
the robot is provided by two PIC16F84 microcontrollers. The
steering servo motor control signal is provided by RB3 off the PIC
microcontroller number 2. The 100:1 gearbox motor is attached to
an H-bridge consisting of components Q1 to Q4, D1 to D4, and R1
to R4. The H-bridge is controlled by the PIC microcontrollers RB1
and RB2 input/output (I/O) lines. Sensor readings of the CdS cell
are read off pin RB4. RB5 reads the tilt switch to check if the robot
has encountered an obstacle. I assembled the entire circuit on two
Team LRN
Behavioral-based robotics, neural networks, nervous nets, and subsumption architecture