• https://www.raspberrypi.org/documentation/hardware/raspberrypi/gpio/README.md
• https://raspberrypi.stackexchange.com/questions/9298/what-is-the-maximum-current-the-gpio-pins-can-output# 50 mA.
• https://elinux.org/RPi_Low-level_peripherals#Internal_Pull-Ups_.26_Pull-Downs
• http://www.raspberrypi.org/documentation/usage/gpio/
• http://makezine.com/projects/tutorial-raspberry-pi-gpio-pins-and-python/# RpI
• https://electronics.stackexchange.com/questions/7423/what-is-a-pull-up-and-pull-down#
• http://razzpisampler.oreilly.com/ch07.html# PullUp are connected to Ground

• https://www.raspberrypi.org/forums/viewtopic.php?t=46525#
• 50kΩ pull up/down resistors

• The pins can only source or sink 16mA so limiting the current to that level (with at least 220 ohms) makes sense.

• http://www.sonelec-musique.com/electronique_theorie_led.html
• http://visualgdb.com/tutorials/raspberry/LED/
• https://vimeo.com/153263103#connected-tizen-20160131rzr#
• https://github.com/mozilla-iot/wiki/wiki/Configuring-GPIO-for-use-with-the-gpio-adapter# IoT

@TaG: RemoteControl InfraRed Io