Abstract: A constant current driving circuit for driving light emitting diodes, wherein a variation detecting circuit comprising a resistor and a field effect transistor is provided and the output voltage of the detecting circuit is effectively used to control the variation of electric current which flows through the driving transistor.

Abstract: In an information processing system controlled systematically by a programable logic array, the initialization of the contents of a predetermined memory circuit after switching-on the power is effected by setting the contents of the memory circuit to an initial value by means of a signal generated automatically or manually.

Abstract: A key input circuit characterized in that a plurality of keys are divided into a plurality of key blocks, that a plurality of series of timing pulses of a first group are supplied to the respective key blocks, each series of timing pulses differing in phase from each other series of timing pulses, thereby to multiplex information on the respective keys of each key block, and that the multiplexed key information from the respective blocks is further multiplexed by a plurality of series of timing pulses of a second group, the timing pulses of the second group being longer in duration than the timing pulses of the first group.

Abstract: A digital display system of the dynamic pulse-lighting type for electronic desk-top calculators and the like, characterized in that a blanking signal having a pulse width large enough to cover each border time between adjacent display timing signals is used to shut off the power supply to the display devices for each pulse duration to suppress any flicker of the display unit which might otherwise result from non-synchronism or overlapping of the display signals.