just wanted to share this info. On our robot for the past few years we have been using a SCSI drive select switch. It digitally selects the decimal values from 0-9, giving us 10 modes in autonomous.
They are inexpensive, and are good for teaching binary math as they wire into 4 digital I/O ports and then do bit math to get the decimal modes.
Here are some examples...
goto here
http://www.scsisource.com/scsi_enclosure_cables/
look for
SCSI ID Selector Switch (0-15) w/selector cable
$6.00
this one would do even more modes than 10 as I state above.
wiring instructions are here...
http://www.wetex.com/downloads/SCSI_ID.PDF
good luck...
Ken Leigh
Team 811 controls Mentor