Paul_KD7HB:
No, not kidding. You think you are detecting people, but you are in fact detecting clothing the people are wearing. And there is your problem using ultrasonic sensors. Some fabric will just absorb the sound, Some will reflect it at an angle, so the receiver will not see it.Paul
Yeah, I got your point. good points.
After I did it by IR sensors, I wanted in first place a sensor that detects long distance,moreover, I watched this video which show what I want to do and he used the ultrasonic sensor.
So what is the best sensor should I use here.