You may not think of salt and sugar as solids because when you see them in the kitchen they are such small particles. But each of these particles is as much a solid as a wooden table, a glass window, or a gold piece of jewelry. A solid is a collection of atoms or molecules that are held together so that, under constant conditions, they maintain a defined shape and size.
Pulse Width Modulation, or PWM, is a technique for getting analog results with digital means. Digital control is used to create a square wave, a signal switched between on and off.
Re: PWM - What is it, How does it work and how to detect it. Thanks, I took my time coming up with this one and I'm glad people appreciate it. There are no lists that I know of, but this would be a good time to start one.