To share with the entire class:

• Arduino Uno microcontroller board, specifically the Arduino Uno - R3 ($30; this simple, stripped-down computer is useful for many "smart" appliance or device projects; in this activity, it receives signals from optical sensors, determines the speed of an object based on the time elapsed between sensors, and sends the latest speed data to a computer monitor; available at: 1) Radioshack, most locations carry the Uno microcontroller on the shelf, and 2) Sparkfun Electronics at https://www.sparkfun.com/, click the Products tab, scroll to the Development boards category to Arduino, and look for DEV-11021, or link directly at https://www.sparkfun.com/products/11021.)

• laptop with Arduino software installed (to install the driver on a PC or Mac, go to https://www.arduino.cc/, click on the Download tab, and follow the installation instructions for your operating system)

• USB cable, standard A-B type (the kind used with most printers)
• 1 medium-size breadboard (available at Radioshack)
• 2 photo interrupters (photo sensors) with 10 mm gap (such as the GP1A57HRJ00F, $2 each, available online at Sparkfun Electronics at https://www.sparkfun.com/products/9299)
• 2 220-ohm resistors (available at Radioshack)
• jumper wire, as needed to complete breadboard circuit (solderless breadboard jumper wire kit available at Radioshack)
• double-sided foam tape or dual-lock tape, a few strips
• 2 sheets of 18" x 24" x 3/16" thick foam core board, white or a light color
• white school glue or foam glue
• duct tape or masking tape, as needed
• BRIO wooden toy train car
• Runaway Train Pre-Activity Assessment, one per student
• Runaway Train Worksheet, one per student
• Runaway Train Post-Activity Assessment, one per student