Breath LED that turn on/off or loop the brightness smoothly.
Dependents: BreathLed-demo EPD_GDE021A1_demo mbed_esp8266_demo NUCLEO_uart_flow_control
This breathing-led uses Ticker and PWM which consumes few CPU, and most important, you can use it to tell system hang.
Just init it with a PWM pin which connected to a LED.