There are lots of discussion regarding comparator, comparator circuit, the regulator circuit, and phototransistors are presented inside the paper. In the paper we can find information about the optical sensor, regulator circuit, interface, and optical sensor interface.
The paper contains discussion around sensor, sensors, circuits, and optical sensors. Below are chosen from this paper:
This paper presents a design for an optical sensor interface to an AFX Digital LED Timer/Counter. The goal of the design is to create a highly reliable circuit which can be made from readily available parts and run off of a single wall power adapter (“wall wart”). All the circuitry must fit inside the base of the timer/counter where the batteries are normally housed. While this circuit is being designed specifically for the Aurora LED Timer/ Counter, the design is generic by nature such that it can be adapted for use with other lap counter systems.
Additionally, this paper gives you info about voltage regulator circuit, optical interface, optical sensor, and the comparator circuit.