An Arduino digital input is one that have one of two states: HIGH or LOW. However, most Arduino implementations also permit you to connect an input whose value can be any value between 0 volts and the power-supply voltage and then convert the input level to an internal digital value between 0 an TODO. The Arduino literature refers to these as “analog” input. The process of coverting a true analog signal to a digital number is called analog to digital conversion (ADC).