Whole Class Activity
In this class discussion you will demonstrate how two robots
communicate with each other. The sample programs provided, Sender and
Receiver work only if the sender has a light sensor and the receiver
can move. Depending on when you decide to introduce this lesson,
students may still have their Roverbots built, or they may already
have other robots such as the Acrobot or the Inventorbot ready. Be
sure to choose one robot with a light sensor (or simply add a light
sensor to it) and one that moves.
Set the robots so that they are within communication range.
Note that they do not have to be pointing at each other in order to
communicate. Turn on both robots and set them to the appropriate
program slots, holding Sender and Receiver. Tell the students that you
are going to shine a light at one robot and ask them to pay attention
to what happens. If needed, repeat this part of the demonstration,
pointing out that both RCXes are running before you shine a light at
one of them.
Students will soon realize that shining a light at one robot
generates a response in the other robot. You can show them that the
longer you wait before shining a light at one, the longer the other
robot waits before moving.
Tell the class that, indeed, the robots communicate. Explain
that one robot sends a message and the other robot has a program set
to receive the message and act on it.
Show the class Transparency #
8. Explain that when two
robots communicate, one sends a message and the other one is set to
receive a message. Point out that the message is just a number; it has
except for setting off a stack of commands in the receiverís program.
It is important that students understand that a robot can
send and receive messages and that an old message must be cleared
before a new message can come in. This concept of clearing a variable
may be foreign to your students. Consider using a container analogy
short set of instructions on a piece of paper (e.g., touch your
forehead 3 times) and tape it to a small container such as a cup, a
jar, or a box.
the range 10 to 20 on a label and tape it to the container.
some numbers on pieces of paper, small enough to fit in the container
and large enough for the students to see. Be sure to have some numbers
between 10 and 20 and some that are outside that range.
the class that you will carry out the instructions attached to the box
each time a message within range arrives.
Emphasize that thereís
one rule: there can only be one message in the box at a time. If the
box is occupied, a new message canít come in.
first number in the box and ask the class:
a) Is the number within the set range?
b) Should I touch my forehead 3 times?
the card in the box, try inserting another message as you remind the
class of the ruleóone message at a time. It will be obvious to the
students that the old message has to be cleared before a new one can
the class that the command to clear the message box is called
Message. Write this command at the end of your set of instructions
and repeat the demonstration one more time.
Have students work in small groups, coordinating the
communication between their RCXes. The Programming Highlights below
explain the commands students must use to set up their senders and