https://raspi.tv/2013/rpi-gpio-basics-6-using-inputs-and-outputs-together-with-rpi-gpio-pull-ups-and-pull-downs https://grantwinney.com/using-pullup-and-pulldown-resistors-on-the-raspberry-pi/
https://raspi.tv/2013/rpi-gpio-basics-6-using-inputs-and-outputs-together-with-rpi-gpio-pull-ups-and-pull-downs
https://grantwinney.com/using-pullup-and-pulldown-resistors-on-the-raspberry-pi/