Light projection type measurement apparatus effectively utilizing a post of a one-chip microcomputer

摘要

A distance measurement apparatus for use in a camera having a CPU. The apparatus has no analog distance-measuring IC and can yet perform active distance measuring. It comprises an infrared-emitting diode (IRED), a light-receiving element and an integration circuit, both connected to the ports of the CPU. In operation, the IRED emits an infrared beam toward an object. The light-receiving element receives the beam reflected form the object and stationary light and converts the beam and the light into an electric signal. The integration circuit integrates the electric signal. The CPU measures a first period of time lapsing from the time when the the integration circuit is initialized to the time when the output of the integration circuit increases over a predetermined value. The CPU also measures a second period of time lapsing from the time when the the integration circuit is initialized to the time when the output of the integration circuit increases over the predetermined value while the IRED is emitting no infrared beam. From the first and second periods of time, thus measured, the CPU determines the distance at which the object is located, not influenced by from the stationary light at all.