Patent ID: 7940253

Claim:
A screen system, comprising: a stylus comprising one or more emitters each operable to emit a pulse; a display; three or more sensors each operable to receive the pulse emitted by the one or more emitters and in response thereto transmit a receive message, wherein each receive message comprises an identifier identifying a respective sensor transmitting the receive message; and a processor connected to the display and to each of the three or more sensors and operable to receive a receive message generated when the pulse is first received by one of the three or more sensors, the processor being configured to count clock pulses until receive messages are received from the remaining two or more sensors to determine a time delay between the first sensor receiving the pulse and each of the remaining two or more sensors receiving the pulse, the processor being further configured to determine a position selected by the stylus using the determined time delays and a plurality of stored time delays for the three or more sensors, wherein position data defining a respective position on the display is associated with each of the stored time delays.