Abstract: An electrooptical display device having, between a pair of electrode plates, a layer of a guest-host, dichroic dye-containing nematic liquid crystal having a positive dielectric anisotropy, wherein optical characteristics of the section of the liquid crystal layer laid between a pair of electrodes formed separately on the electrode plates are made substantially equal, when no voltage is applied between the electrodes, to optical characteristics of the other section of the liquid crystal layer corresponding to the background, thereby providing a good positive display, that is, the formation of a colored display pattern distinctly discernible on a colorless or light-colored background.

Abstract: A miniature DC motor is connected to a DC source through a PNP type driving transistor. The back electromotive force of the motor which is proportional to the speed is applied to the base electrode of an NPN type control transistor through a variable resistor and the output of the control transistor is applied to the base electrode of the driving transistor through an NPN type amplifier transistor. A capacitor is connected between the base and emitter electrodes of the control transistor for smoothing the voltage applied to the base electrode of the control transistor. The sensitivity of the speed control system can be improved by connecting a Zener diode in the input circuit to the control transistor. Further the effect of the variation in the ambient temperature can be compensated for by using a thermister.