Potato Gun Photogate

https://github.com/bshambaugh/BWPhotogate/blob/master/photogate.ino

 (inset photogate2 code from laptop here)
http://www.atmel.com/images/atmel-8271-8-bit-avr-microcontroller-atmega48a-48pa-88a-88pa-168a-168pa-328-328p_datasheet_complete.pdf

http://www.dfrobot.com/wiki/index.php?title=Arduino_LCD_KeyPad_Shield_(SKU:_DFR0009

http://www.mouser.com/ds/2/268/21733h-26779.pdf (op amp)

http://www.analog.com/library/analogDialogue/archives/43-09/Edch%201%20op%20amps.pdf

https://en.wikipedia.org/wiki/Photodiode