Every pin of Atmel microcontroler ( it's also apply for great majority others IC manufacturers ) is internally protected by couples diodes. It works for current < 1 - 5 mA, which is true with piezo sensors.
Every pin of Atmel microcontroler ( it's also apply for great majority others IC manufacturers ) is internally protected by couples diodes. It works for current < 1 - 5 mA, which is true with piezo sensors.