Pulse Width Modulation (PWM) is a typical example of digital to analog conversion. By pulsing between 1 and 0 at different frequencies, a digital (binary) signal can mimic many different values. Arduino has a great tutorial on PWM . The wikipedia page is helpful but also TMI. The bottom line is PWM is a great way to output a smooth continuous signal on a wire that is actually only capable of outputting ones and zeros. Applications include fading an LED, mixing colors on LEDs , controlling servo motors , controlling the speed of DC motors, like this pump , or making different sounds on a piezo buzzer. Pulse width modulation is activated by the Arduino function analogWrite .