The digital pins on the Arduino board can be set (with code) to output either HIGH (5V) or LOW (0V) — essentially ON or OFF. This is great for applications like blinking LEDs or activating relays.

But what if we wanted an output voltage somewhere in between 0V and 5V? This might be useful in applications like controlling the speed of a DC motor, or “dimming” an LED.

Well, the digital pins cannot directly produce an analog voltage; as we’ve said, they’re either HIGH or LOW. But it turns out we can simulate these “in-between” voltages using a technique called Pulse Width Modulation, or PWM.

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