Sweet by David Cook

Sweet is a line-following robot made from a metal candy 
container. The robot follows either light or dark lines. When
someone presses the exhaust-pipe switch, the robot 
determines the type of line by comparing the edge sensors to the
center sensors. Then, the robot races away!

Six phototransistors are located under the front. If a 
high-contrast line is used, the robot handles 90-degree turns
and can stop when the line ends. If the surface contrast 
is poor, the robot can still follow tiny differences because
of an autocontrasting algorithm applied after each sensor read.

For fun, Sweet's grill includes a 10-segment LED bar graph. 
A red pulse sweeps back and forth while driving, and
indicates the line location when stopped.

It took one and a half calendar months (evenings and weekends) 
to design and build. Reusing code and designs from a
recent mini Sumo robot saved a lot of time. Also, I made my 
own circuit boards for the first time, which took some time
to learn, but saved time in wiring.

Cost:
 $ 5 candy can (less candy)
 $ 8 MC68HC08GP32 microcontroller
 $20 motors
 $ 5 tires, hubs
 $10 emitters and detectors
 $20 rechargeable batteries
 $10 PCB copper boards
 $ 5 switches
 $10 MOSFET H-bridge 
 $20 buttons, capacitors, resistors, diodes, nuts, bolts,
     solder, paint, wires, Velcro, connectors
 $ 7 LCD
The total is around $120.

More information and pictures of Sweet can be found at 
http://www.robotroom.com/Sweet.html

Email: david@robotroom.com