Chapter 1, page 11 This code is basic but allows the reader to gain insight into key elements for several other projects in this book. It combines two pieces of code that are listed in the examples ...

Pin 9 generates a PWM signal using a time-honored technique. Suppose you want to generate 20/255 (about 8% duty cycle). You take an 8-bit accumulator and add 20 to it repeatedly.

Pulse-width modulation (PWM) Pulse width modulation (PWM) is a powerful technique for controlling analog circuits with a microprocessor’s digital outputs. Pulse-width modulation,as it applies to LED ...

But generating a smooth voltage in this way takes just a few more parts. [Scott Daniels] spent some time discussing the process of smoothing a PWM output by using a low pass filter.