Page 460 - Robot Builder's Bonanza

PROGRAMMED BRAINS 429

Figure 34- 1 A few parts from
basic electronic components form a
Photo Resistor
transistor workable robotic brain. Depending
on how the parts are configured,
Output
Output the robot can display different
“behaviors.” In one variation of
Resistor this light- detection circuit, the
Photo
transistor rebot responds to light; in the other
variation, the robot responds to
darkness.

Figure 34- 1 shows a common form of robot brain made from from simple parts. Wired
one way, this brain makes the robot reverse direction when it sees a bright light. The circuit
is simple, as is the functionality of the robot: light shining on the photodetector might turn
on a relay or actuate some other circuit.
Variations of this circuit could make the robot stop when it sees a bright light. By using two
sensors, each connected to separate motors, you can make the robot follow a bright light
source as it moves. By simply reversing the sensor connections to the motors, you can make
the robot behave in the opposite manner: it steers away from the light source, instead of
driv ing toward it.
You could add additional simple circuitry to extend the functionality of robots that use dis-
crete components for brains. For instance, you could use an LM555 timer as a time delay:
trigger the timer and it runs for 5 or 6 seconds, then stops. You could wire the LM555 to a
relay so it applies juice only for a specific amount of time. (This is the basic function of the
enhanced RBB Bot in the My First Robot lessons.) In a two- motor robot, and using two
LM555 timers with different time delays, your robot can be made to steer around things.

Programmed Brains

Perhaps the biggest downside of making robot brains from discrete components is that
because the brains are hardwired as circuitry, changing the behavior of the machine requires
considerable work. You need to either change the wires around or add and remove compo-
nents. Using a solderless breadboard (see Chapter 32) makes it easier to try out different
designs simply by plugging in components. But this soon gets tiresome and can lead to errors
because parts can work loose from the board.
You can “rewire” a robot controlled by a computer simply by changing the software run-
ning on the computer. For example, if your robot has two light sensors and two motors, you
don’t need to do much more than change a few lines of programming code to make the robot
come toward a light source rather than move away from it.

TYPES OF PROGRAMMABLE GRAY MATTER
An almost endless variety of computers and computer- like devices can be used as a robot
brain. The five most common are:

• Microcontroller. A microcontroller is programmed in either assembly language or a high-
level language such as Basic or C. Figure 34- 2 shows a Parallax BOE- Bot robot kit, which

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