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Features The controller in our MicroMouse is based on MIT's Handy Board. Because the Handy Board is a Motorola 68HC11-based board designed for experimental mobile robotics work, we thought it would be a good starting point for our controller. We then modified the design by eliminating features that we did not need and adding features that we required. In the end, we wound up with a MicroMouse with the following:
We built our version of the controller board using perf-board. Instead of one large board, we designed the controller as 3 separate boards that sandwich together. The topmost board is the main microcontroller board and contains among other things the 68HC11, the RAM, LCD display and speaker.
The Microcontroller Board
The middle board takes data from the wall sensors and feeds them to the main board. It also contains the latch chips that control the motor driver chips on the third board.
The Sensor Board
The sensor assembly holds eleven IR sensors, 5 on each side and one in the front. All cables are routed to a connector that plugs into the sensor board.
The Wall Sensor Assembly Each sensor is composed of an IR emitter and an IR sensor housed in one package. As an aid when adjusting the sensors, the robot can be put into "diagnostic mode" where the value of the sensors is displayed on the LCD panel.
The Left Sensors
The bottom board serves two functions. It contains the stepper motor driver chips which control the motors and it converts the 12v from the batteries or power supply to the 5v required by the logic chips.
The Motor / Power Board
The three boards are designed to be plugged together and the entire package fits neatly into the lid of the acrylic case.
The Complete Microcontroller Assembly
The programming cable contains the MAX232 chip which translates the voltage levels so that the 68HC11 can communicate with a standard PC serial port. One end of the cable contains a DB9 connector for plugging into the PC, the other end contains a standard 6 conductor telephone plug which connects to the microcontroller board (you can see the square hole cut into the acrylic case in the photo above).
The Programming Cable
The motors were mounted in a wheelchair design on either side of the case. This left just enough room behind the motors for 8 AAA batteries and its holder. Using alkaline batteries, the mouse is capable of running up to 1/2 hour, more than enough time for a competition.
The Two Stepper Motors Mounted in the Acrylic Case and the Battery Pack
Since the mouse only has two drive wheels, it needs a balance point in the rear of the chassis. This was accomplished by creating a custom-built castor. Because of the low friction, the mouse is able to make very smooth turns.
The Custom Castor |
Click here to view an explanation of the major components on the microcontroller board.
