Abstract: This invention relates to a photoelectric switch and a photoelectric detector for detecting the presence or absence of an object by using a light, and more particularly to prevention of mutual interference in the case of using a plurality of photoelectric switches. For example, an LED in a light emitting unit intermittently emits a sensing light at the timing of an output pulse from a pulse generator. The resultant pulse is divided in frequency by a frequency divider and then delayed by a one-shot circuit. At the timing of an output pulse from the one-shot circuit, another LED emits a transmission light to a photoelectric switch at next stage. Therefore, the transmission light is always delayed from the sensing light. The transmission light from the preceding photoelectric switch of the same construction is received by a photodiode, and an output pulse is outputted from a pulse generator in synchronism with a synch timing signal produced from the light receiving unit.

Abstract: An illumination type optical recorded information reading device including a plurality of light emitting elements, a photo detector for detecting optical indication on a media and converting the detected indication to electrical information, a plurality of driving elements for driving the light emitting elements, a driving current detector for detecting a total value of driving currents flowing through the driving elements, and a controller for comparing the total value with a reference value and generating a control signal to the driving elements so as to make a difference between the total value and the reference value constant.

Abstract: In a code reading device, which receives reflected light obtained by scanning a code represented on a recording medium with a laser light beam and decodes it to obtain the code, the reading probability is improved by varying the focusing position for every scanning period with the laser light beam.