====== LowPower ======


  * https://github.com/rocketscream/Low-Power
  * https://github.com/chacal/stm32sleep
  * https://www.youtube.com/watch?v=IYuYTfO6iOs
  * http://www.astromik.org/raspi/krmitko/index.htm
  * https://www.arduinotech.cz/inpage/konstrukce-realneho-cidla-sigfox-s-wisol-arduino-i/
  * http://www.gammon.com.au/power
  * https://randomnerdtutorials.com/esp8266-voltage-regulator-lipo-and-li-ion-batteries/