Here's an interesting idea - being able to place a physical knob or switch onto a virtual control displayed on a laptop LCD screen and use it - instead of a mouse or keyboard - to control an application. A 3-dimensional control surface prototype called SenseSurface allows you to do just that, as demonstrated in the following very short (00:10) video showing a working potentiometer prototype connected to an oscilloscope:
The SenseSurface prototype is said to work with most laptop PCs with a USB input, and consists of low-friction magnetic sensing knobs and a sensing x/y matrix that's attached to the rear of the laptop's screen. The fixed-base knobs contain custom designed movement sensors that determine position within a range of 180° with a 10-bit digital output and can be repositioned simply by picking them up and repositioning them on the LCD screen.
According to the prototype's designer, linear sliders and switches can also be used on the LCD surface. Other controls and surfaces currently being tested include pressure controlled analog touch switches, squeezy knobs and balls, textured rubber, and vibration feedback. SenseSurface is expected to cost less than $100 in production.