This circuit lets you design your own robot to suit your own taste. It would not be difficult, for instance, to convert this design to a credible R2D2, without any modification to the PC board. With a little imagination, the possibilities would be even wider. The circuit could operate a pulley system, serve as a line-tracker or rotate motors in response to broken beams of varying intensity, without modification to the PC board.

As noted, the robot is programmable. Therefore, the drive circuit is merely a slave to the software and is of a relatively simple design. The circuit is based on a PICAXE-08 micro, as has been featured previously in SILICON CHIP. Although more limited than a "raw" microcontroller, it is a small marvel nonetheless – both for cutting out the need for a costly programmer and for placing respectable power at the service of the constructor with great simplicity.

All that the Programmable Robot requires in its support is a PC and a serial cable. The programming software is free www.rev-ed.co.uk and comes in the form of a telegram-style BASIC and flowchart programming.

Note that the Programmable Robot’s memory is limited – not all the features listed above can be used at the same time. However, with careful programming, the robot will perform most dual or even triple tasks with aplomb. As an example, light-seeking, bump-and-respond and sound can all be incorporated in a single program.

Since the PICAXE-08 microcontroller represents the Programmable Robot’s "control room", this is where we shall begin. Unfortunately, the PICAXE-08 is confusing in its pin numbering, which has become something of a legend in its own time – therefore we shall resort to the standard IC pin numbering here; ie, pins 1-8, with pin 1 being situated next to the small indentation on top of the IC.