https://www.youtube.com/watch?v=TjzFo63svmM
https://patents.google.com/patent/US6658577B2/en
https://avital.ca/notes/a-closer-look-at-apples-breathing-light
https://sean.voisen.org/blog/2011/10/breathing-led-with-arduino/
http://me120.mme.pdx.edu/lib/exe/fetch.php?media=notes:breathing_led_equations.pdf