Abstract: End-of-ribbon sensor circuitry for use with an end-of-ribbon sensor of an electronic typing system comprises an input voltage divider for receiving the output signal of the end-of-ribbon sensor. The two signals from the voltage divider are applied to a differentiating circuit providing different time constants to the two signals. The differentiating circuit compensates for varying conditions of ambient light within the ribbon cartridge and provides a delay which eliminates false signals due to rapid fluctuations of the ribbon. After differentiation, the two signals are compared utilizing delayed switching time to determine the presence of an end-of-ribbon signal. The output, if any, of the comparator is applied to a sampling circuit where the signal is sampled for a predetermined period of time after the print hammer is fired.

Abstract: An end-of-ribbon sensor for use with an electronic typing system comprises a housing which protrudes from a mounting block and plate attached to the ribbon cartridge mounting plate. The housing protrudes through an aperture in the ribbon cartridge and within the interior volume thereof and contains a light source for directing a beam of light at a predetermined angle at the ribbon and a light detector directed at a predetermined angle for receiving the reflected light. Upon sensing a reflective marker attached to the ribbon, the output of the sensor provides an appropriate signal indicating the end-of-ribbon. The housing also comprises a portion of the mounting means for the ribbon cartridge.