Before You Begin


What’s the point? Working with RCX messages may help students develop a better understanding of how input is used by a program to determine its path. Since they set up a message as a numeric value transmitted via infrared, it may become clearer to students that a program processes input digitally.

Identifying attributes shared by the light sensor watcher and the message watcher (both work with ranges of values) may help students form a more general view of sensor input and how it affects a program.



What you will need:

   For each group:

·     The Robotics Inventions™ kit

·     A disk

·     A copy of the Technical Guide

·  Any two pre-built robots (will need to coordinate with another group)

·     A small flashlight

·     A building bin (optional)

·     Student activity sheets



   For the class: (Demonstration)

·     2 pre-built robots, one with a light sensor, and the other without a light sensor

·     A flashlight

·     Transparencies # 8 and 9


Programs used: Sender; Receiver

Prepare Ahead:

1.       Make enough copies of the RCX to RCX Communication student activity sheets for each student to have one.

2.       Download the program Sender onto a robot with a light sensor.

3.       Download the program Receiver onto another robot (preferably a vehicle).

4.       Prepare the materials needed for the “container analogy”. (See page 7-3 for details.)

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New commands introduced in this activity:


Tech Guide
© The LEGO Group



  Tech Guide
© The LEGO Group


            Tech Guide

            Tech Guide

             Tech Guide

           Tech Guide
© The LEGO Group

Activity Overview

This activity is designed to give students additional and somewhat more complex problems to solve. Introducing the RCX to RCX communication creates opportunities for students from different groups to work together because two robots are needed to establish communication, and each group has only one robot.


You will decide whether to introduce this activity while students are still working with Roverbot or whether to postpone it until they build new robots. By now, students might be asking to build something new. If this is the case, we suggest delaying the introduction of this section until after they have had a chance to build a robot of their choice. Also, having different kinds of robots communicate with each other may inspire students to come up with new project ideas.


First you will show the class how one robot is activated by another one. You will tell the class that you have two robots, one with a light sensor and the other without, explaining that you will set the robot that doesn’t have a light sensor in motion using a flashlight. You will then show the class the programs that run these robots and explain the relationships between the sender and the receiver.


It is important for students to understand that for a receiver to get more than one message, an old message has to be cleared before a new one can be received. You will use a container analogy in a class discussion to illustrate this point.

Students will then follow the RCX to RCX communication activity sheet, first figuring out how to set up communication between two robots, and then solving some problems.

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