Customizable control system

A system, comprising:

• an electronic device comprising a display with a surface, wherein the display is configured to display encoder marks;
• a repositionable control device at a location on the surface of the display, the repositionable control device having a housing that is removably attached to the display and at least two light sensors in the housing, wherein the housing has a fixed portion and a rotating portion, wherein the at least two light sensors monitor the display encoder marks as the rotating portion rotates about the fixed portion, and a wireless power receiver in the housing that receives wireless transmitted power from the electronic device;
• and
• control circuitry in the electronic device that is configured to direct the display to emit light through the surface using a predetermined time-varying pattern while the light sensors make measurements on the emitted light and that is configured to identify the location on the surface of the display based at least partly on the measurements on the emitted light by the light sensors, wherein the predetermined time-varying pattern includes regions of dark pixels and regions of bright pixels, and wherein a selected one of the regions of the dark pixels and the regions of the bright pixels extends across at least half of the display.

A repositionable knob configured to be magnetically mounted on a display surface associated with a display, wherein the display is configured to display encoder marks, comprising:

• a housing containing wireless power receiver circuitry that is configured to receive wirelessly transmitted power;
• a touch screen display mounted in the housing;
• a rotating portion that rotates relative to the housing;
• a photodetector on the rotating portion that monitors the display encoder marks as the rotating portion rotates;
• and
• communications circuitry that wirelessly transmits knob rotational information indicative of an angular orientation of the rotating portion relative to the housing.