Abstract: A light pen computer interface system utilizes a coil located externally of the computer's CRT display monitor to sense the magnetic field which provides the raster for the CRT. Vertical and horizontal sync detection circuits receive the sensor coil output and supply vertical and horizontal sync signals to a timing circuit. The timing circuit in response to an output signal from the light pen and the vertical and horizontal sync signals supplies a pen position signal to the computer which is either representative of the x,y coordinates position of the light pen on the CRT screen or representative of the change of x,y coordinates between successive positions of the light pen.

Abstract: A unitary hand-held wand incorporates two optical inputs with complete optical and electrical isolation between each of the inputs. In the illustrated embodiment the opto-electrical transducers include a light pen assembly and bar code sensor assembly. Each assembly is included within a housing which is divided into two substantially optically isolated cavities. The light pen assembly is disposed in one cavity and the bar code assembly in the other. The electrical portions of the light pen assembly and bar code assembly are each provided with electrical shields which are electrically isolated from their respective assemblies. The shields are in turn selectively coupled either to the power source ground or chassis ground. The light pen assembly and bar code assembly further include high gain preamplifiers which are additionally electrically shielded by a preamplifier shield.