Abstract: A colorimetric circuit comprising three detectors for detecting red, green and blue components respectively, a memory for storing the outputs of the detectors sampled at the same instant in logarithmically compressed form, and a control circuit for reading out the contents of the memory in sequence, thereby it being made possible to improve the accuracy of colorimetry.

Abstract: A stepping motor drive device including a comparator for comparing the number of drive steps with a prescribed value and a control circuit for changing the operation of the stepping motor between a 1-2 phase excitation drive mode and a 2-phase excitation drive mode based on the comparison result of the comparator.

Abstract: A power source system including a power source device and an external device connected to said power source device, in which the connection between the power source device with the external device is firstly confirmed, then the power is supplied from the power source device to the external device when a predetermined output of said power source device has been obtained, while a first signal is transmitted from said power source device to the external device connected thereto, and the supply of power is stopped if a predetermined signal is not fed from said external device.