This Demo was designed for really small processor but can work on every one, in case of a rapid blinking led folowing a pause, it means the stak memory sice needs to be adjusted, count the rapid one to know what thread is compromised.

was tested with ATTiny85 and 84, Arduino NANO, MKZERO, Bluepill, ESP8266, DUE, AVR MEGAs

pins 1, 2, 3, 4