Review on DROK 180047 High Conversion Efficiency Power Converter Step-down Female USB Adapter 12V to 5V - Max 3A/15W Output for iPhone/HTC/Nokia by Jeremiah Vishwasrao

This is a great product considering the price. Just plug it in and it controls your computer's system volume like any other multimedia keyboard. It rotates smoothly with a medium detent or click and marks increments. No setup, no software installation, no additional power supply. High marks for ease of use. Remember this is a cheap plastic product. The top swings on the base when you push it sideways. The base is light enough that it sometimes slips when you rotate the top quickly. If that bothers you, use double-sided tape to attach the base to a heavy, non-slip surface (like a cup holder) or to your desk.