The Scribbler robot is a combined effort of three companies: Parallax, Inc.; Element Producs, Inc.; and Bueno Systems, Inc. It's a very inexpensive differential steer robot that's an ideal platform for children to learn on or hackers to use as a base. It includes enough built-in sensors to perform a variety of common robot behaviors out-of-the-box including line-following, obstacle avoidance, and light seeking. The robot is controlled by a Basic Stamp which can be programmed by the user. We provided our review unit to Dick Swan of the Dallas Personal Robotics Group recently and he has written a detailed review complete with photos and disassembled views of the interior.

Scribbler Robot Review by Dick Swan

The Scribbler Robot from Parallax is a great introductory robot. For $100 it comes loaded with features and capabilities not found in many more expensive platforms. It comes preloaded with several built-in programs; as your skills advance there are two levels of user programming capabilities for writing your own autonomous behavior.

The unit is pre-assembled and is ready to run out of the box with the addition of six AA batteries (not included). Unfortunately, there is no expansion capability for hardware enhancement.

The pre-assembled unit is great for the beginning user or the hardware challenged. Capabilities of the Scribbler include:

Top and bottom views of Scribbler Robot

• Separate motors for left and right wheel drive. Turning the scribbler is accomplished by applying different power levels to the motors.
• Two infrared detectors on the bottom of the robot used in line following. The detectors provide a binary output --- either light or dark detected.
• A single infrared distance or obstacle detector on the front center of the Scribbler. Two separate infrared sources are mounted on the left and right side of the robot. By selectively enabling either of these the Scribbler does left or right distance/obstacle detection.
• Three photocell detectors on the top front of the Scribbler. These are used to provide a three-bit input value for starting up one of the preprogrammed robots. You simply optionally place fingers over the detectors to change the reading.
• A speaker for tone and melody generation.
• A motor stall sensor to prevent burnout.

Pre-Installed Programs

The Scribbler comes with eight pre-installed programs. Program selection is via the three-photocell inputs on the top of the Scribbler. The more useful programs include "light seeking behavior", "object detection and avoidance while moving" and "following a line".

A cool capability of the scribbler is a hole on the top for insertion of a felt tipped pen. The pen provides a record of the Scribbler's movement.

It's fun to play with these programs a few times, but then you'll be ready to take on more challenges. Fortunately, the Scribbler is designed for the end-user to write his own programs.

Screen capture of Windows GUI software

User Programming

Once you've played with the built-in programs, you'll want to program the Scribbler yourself. This can be easily accomplished on a standard (Windows only) computer. A first step would be to reproduce or improve on the built-in programs. Source code for the built-in programs is very easy to use and is included on the Scribber CD.

The Scribbler intelligence is provided through an internal Basic Stamp processor. It can be programmed via the RS-232 serial connection on the top of the robot. The appropriate cable is included in the Scribbler kit. For the modern computer without a serial (COM) port, you'll need an USB-to-serial adaptor available at many computer stores for $15 to $25.

Parallax has provided two programming environments for the Scribbler. A basic graphical oriented solution and a text based programming solution using the basic language for the Stamp.

Graphical Programming Interface

The graphical interface is intuitive and easy to learn and, with only a little adult supervision, could be used by a middle-school student. Parallax recommends age 8+. You simply drag and drop icons (graphical objects); each block performs a function (check sensor values, drive motors at certain speeds, etc). Once downloaded to the Scribbler the program is "executed" in the order that the blocks are linked together. Control blocks are provided for modifying the Scribbler's behavior including blocks for branching, subroutines, looping, etc.

To program your robot, you drag icons from the left menu onto the programming screen. The icons are linked together and the Scribbler will execute them in order.

Programs are downloaded to the Scribbler over a cable connecting a COM port on your PC to the connector on the Scribbler.

Screen capture of Windows PBASIC software

"PBasic" Text Based Programming Interface

Once you've mastered the Scribbler GUI, you may want to program the Scribbler using the Basic programming language. Parallax provides their version of Basic for the Stamp processor on the enclosed CD. Summary

The Scribbler is not the fastest running Robot. Its fastest speed is about 1.5 feet per second. This is good performance but not great; a very fast hobbyist robot can do 3 fps or more. The speed is a good match to typical line following solutions where line is about 1" wide; for narrower lines, or tight turns, the scribbler is unable to track the line.

At $100, the Scribbler delivers great value when compared to other introductory robots.

Opening up the Scribbler

Editors Note: The Scribbler is supported out-of-the-box only on Windows. What about Linux and Mac users? There's good news and bad news. The bad news is that there's no official software solution yet. The good news is that, if you're a Perl hacker, you may have a head start. A Scribbler source code package has been released as Free Software licensed under the GNU GPL. It's written and Perl but was developed under ActiveState Perl for Windows, so some porting will be needed to get it to run under a normal Perl environment on a Linux or Mac box. You can find the software in the "Hacker's Haven" section of the official discussion forum.