Ken Warwick

Background I have been mousing for about 6 years and have managed to collect a couple of cheeses. I started with tricycle stepper motor designs but now favour front wheel steered DC motor arrangement. Last year's machine - Busy Lizzie - came second at Exeter. Millennium Bug The Bug is similar to last years design, with the general idea of producing a lighter weight mouse (12 ozs) which will aid acceleration and deceleration when running and turning. The nose wheel is steered with a modified R/C servo. This wheel is also coupled to an optical reader (cannibalised from a PC mouse) which produces 34 pulses per wheel revolution. This is effectively doubled by sensing both the leading and trailing pulse edges. The rear wheels are driven by a pair of old Futaba miniature servos with gear train modified and pot removed. The computer is a very small unit, EM320 by Devantech using a Dallas 8OC320 running at 20Mhz.

Power supply is 5 NIMH cells 2/3 AA size using 2930 low dropout regulators to provide separate 5v rails for computer and servo.

Uses infra-red sensing over the walls - rows of 5 sensors each side with outer/inner pairs coupled together plus one front sensor to check for front wall (7 points to read). The software provides the steering pulse (about 1mS) every 15mS and during this period all other repetitive functions are executed - sensors read, update wall map, solve maze algorithm, motor on pulse etc.

To keep currents low the 11 sensor emitter diodes are in series and are therefore pulsed simultaneously for just long enough to read the 7 sensor outputs via an addressable analogue switch (405 1). The 20v power supply for the emitters is a miniature 5 to 15v converter with limiting resistor. Motors are switched and reversed using 2919 bridge motor driver and braking uses resistors across motors switched in by Mosfet relays.

Current build state - hardware virtually complete but untested.

ken.warwick@cw.com