hardware interrupts

Mastering Arduino Part 9 card (horizontal)
Mastering Arduino Part 9: Rotary Encoders and Quadrature Input
Arduino DIY Electronics
Decode rotary encoder position and direction with interrupts, Gray-code state tables, measured detents, LEDs, and a reliably debounced reset button.
Mastering Arduino Part 8 card (horizontal)
Mastering Arduino Part 8: Interrupts: Reacting Without Polling
Arduino DIY Electronics
Learn attachInterrupt(), ISR rules, volatile data sharing, and when polling is enough by building a pulse monitor that proves which events get missed.