Smectic liquid-crystal flat display with light-pen and readout functions

A thermally addressed smectic liquid-crystal flat display is described, which is addressed by a laser-diode light pen as well as by the usual heating electrodes. Information can be written manually on the display panel using a laser diode or information generated by external equipment can be displayed by resistive heating in a line-at-a-time sequence. The manually written information can also be read out electrically by detecting the capacitance of each pixel. To detect the pixel´s capacitances arranged in X-Y matrix form, we describe a scheme to prevent crosstalk and to avoid the influence of the electrodes´ resistance. By using these techniques, we constructed an experimental display, It has a 30 × 40 mm²display area and a resolution of 4 lines/mm.