Apparatus for detecting the number of objects

摘要

Apparatus for detecting the number of objects such as the number of persons located within a predetermined area. Ultrasonic wave is emitted toward the objects, the number of which is to be determined, and the reflected waves from the objects are received by a receiver. Among the received reflection waves, the waves having an amplitude greater than a predetermined peak value are derived as the useful reflection wave signal having a constant peak value. The number of the objects is determined based on the quantity of the derived reflection wave signals having the constant peak value. By emitting the ultrasonic wave for every unit time, the derived reflection wave signals having the constant peak value may be averaged by means of a smoothing circuit.