PETER BALCH

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The Picobotz has been designed as part of the iBotz range for iBotz Ltd. It is also available from many other suppliers. Please Google for it.

The Picobotz contains a PIC processor running at 4M instructions per second. It can be programmed with up to 180 instructions. The programs are written on a PC running Windows and downloaded into the Picobotz through an RS232 port.

The Picobotz has the following analogue sensors:
  • visible-light obstacle detector - works up to 15cm
  • visible-light level
  • line follower
  • microphone measures sound level and length

It has two drive motors and a sounder which can produce a variety of beeps and chirps.

The Picobotz is agood introduction to programmable robotics. It has three sensors: a line-follower, a sound sensor and an obstacle detector. The line-follower can follow a black line on a white surface using a pair of phototransistors and a bright LED. The sound-sensor can distinguish between a short sound, such as a handclap, and a long sound, such as a whistle. The obstacle detector flashes a bright red LED and looks for a reflection; it can also be used to measure the overall light level. There is a small piezo loudspeaker which can make a large range of beeps and whistles.

The wheels are driven by two preassembled motor-gearboxes that give a smooth, quiet drive.

The Picobotz is programmed from a PC running Windows. Programs are downloaded over a serial cable. Your computer should have a serial port or you could use a USB-to-serial convertor.

The Kit

The kit includes all the parts you need, including three pre-soldered circuit boards, two motor-gearboxes, and injection moulded plastic parts that screw together nicely.

Assembly should take under an hour for a moderately experienced constructor. A child would take longer and might need adult advice. The only tool needed is a small Phillips screwdriver. A 9V PP3 battery and two AA cells are required (not included).

A 85x85cm folded paper with a printed track for line following is included.

The 40-page instruction manual also contains a brief history of robotics. There is a complete schematic diagram and a description of the circuit (neither of which is needed but would interest an electronic hobbyist).

Sensors

The Picobotz, has two photo-sensors for line following, and so performs better than robots with just one sensor which can only follow an "edge".

The obstacle sensor uses a very bright red LED instead of an infrared LED (as does the line sensor). It works surprisingly well and can easily detect obstacles up to 15cm away. Because it uses visible light, it can also detect the general illumination level in front of the robot. The circuit has been optimised for detecting obstacles so, when measuring the background light level, it is not very sensitive. However it can easily "see" a desk lamp or a window

The microphone is good at detecting handclaps but it can be hard to make a sufficiently loud "long" sound - whistling works best. The sensitivity of the microphone and the centre-point of the line follower, can be adjusted with preset resistors.

The length of a "long" versus "short" sound, the threshold for the background light level and the threshold for obstacle detection can all be adjusted in software via a PC. The PC can also show a real-time display of sensor values.

Programming

The Picobotz is programmed from a PC running Windows. Programs are downloaded over a serial cable. Your computer should have a serial port or you could use a USB-to-serial convertor. If you want to try out the programming system, you can download it.

  • Computer requirements:
    • PC running Microsoft Windows® 95, 98, 2000, ME, XP
    • 64Mb RAM
    • 5Mb free disk space (200Mb preferred for tutorials)
    • 300MHz processor
    • CD reader
    • tutorial requires soundcard and speakers/headphones
    • RS232 COM port

The programming editor has a point-and-click interface.



There are instructions to control the motors and to follow a line, to read the sensors and to create hundreds of different beeps and whisles. The usual program control statements, If, While, For and Repeat are available along with begin-end block structures. If, While and Repeat instructions test the status of the different sensors.

Sensor readings can also trigger "Events". Events are rather like interrupts and are triggered instanly rather than, for instance, at the end of a loop.

Documentation

An hour of computer-based tutorial matter is included which is suitable to a bright 10-year-old. The same tutorials are available on the CD as a 15-page programming manual.

There is a complete description of the serial communications format and of the program instructions codes so you could develop your own programming editor for another operating system or a different language.


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Questions or comments ? E-mail me at peterbalch@btinternet.com

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