https://www.youtube.com/watch?v=x2EuYqj_0Uk'
http://www.seattlerobotics.org/encoder/mar97/basics.html
https://learn.sparkfun.com/tutorials/pull-up-resistors
http://playground.arduino.cc/CommonTopics/PullUpDownResistor
http://playground.arduino.cc/CommonTopics/PullUpDownResistor