A touch-sensitive overlay (20) for cooperative, optically proximate engagement with a visual display (22) of luminous character information (38) latently occupying one or more of a plurality of character locations (26) defined with a position-multiplexed coordinate array one from another, is comprised of a mask (44) of a photoreactive transducer (52) having at least one photoelectric parameter which varies as a function of incident light from the display of character information striking the transducer, and a signal circuit element (92) responsive to a variation in the photoelectric parameter in communication with the mask for developing a characteristic logic pulse indicative of the position of one or more character locations within the array upon a touch thereof and the coincident presence of character information thereat (48). In a highly preferred implementation, the visual display is a CRT display where the raster scan (24) and associated driving circuitry (96) provides the position-multiplexing of character locations and selective illumination thereof, while the photoreactive transducer is an open photovoltaic cell for developing a localized electric potential at luminous character locations, completed upon a manual touch by the operator at a selected location to develop an output voltage pulse indicative of the position(s) touched, which pulse is then employed to interrogate registers (98) associated with the raster scan circuitry in order to provide spatial determination of the location(s) corresponding to the coincident presence of a touch and luminous character information thereat.

A computer input device uses an ordinary sheet material such as a card, letter or envelope to select and point to a symbol. A remote portion of the sheet material covers sensors which sense available ambient light. Uncovered sensors provide background light information. A single sensor is associated with multiple symbols and is associated with symbols in at least two specific groups of symbols. A processor is connected to a demultiplexer and a multiplexer, and the demultiplexer and multiplexer are connected to individual sensors. Biasing resistors are connected to individual sensors. The processor selects a pair of connectors from the demultiplexer and multiplexer, thus sampling a particular sensor. The output of that sensor is converted a digital signal, which is sent to the processor and stored in a random access memory. After sufficient sensors have been interrogated, the processor provides an output which is particularly related to the sensor or group of sensors which are covered by the pointer sheet, and which is specifically related to a symbol pointed to by the pointer sheet. In one embodiment, the processor output is displayed as a particular information. In one embodiment, the processor output illuminates lamps over individual receiver bins to indicate the receiver bin in which the pointer piece should be deposited.

A light-emitting diode is used both for receiving data from an operator to change the logic state of a device and for displaying the entered data back to the operator. Current is selectively applied to the diode to display the data, but on an alternate basis the photo-current produced in the light-emitting diode by surrounding illumination is sensed and the data are received by detecting the fall-off in the photo-current caused by the operator covering the light-emitting diode. This technique is advantageously employed for the input and display of ink slide settings for a rotary printing machine by using a light-emitting diode matrix or bar graph display subject to finger-tip control by the operator. The diode matrix is scanned by repetitively and sequentially inhibiting the lighting current to the individual light-emitting diodes so that they may be sequentially connected to a photo-current monitoring circuit via a multiplexer under control of a clock circuit.