Author Options:

need help with ir object detecor (reflect theory)? Answered

i'm working on a small project using iri want to make an object detector for detecting people who stand in front of a door i don't want to use laser or ir beam cut theory
i want to use reflecting theory
so that the sender and reciver be in the same side
just as supermarkets doors
i have searched for many circuits but they all use cut theory
this site is my local store that have parts in my country


The trouble with PASSIVE IR is that as soon as the target stops moving, so does the signal. These things rely on movement to create the output signal.

ACTIVE IR isn't too hard to arrange these days, but the trick is recovering the received signal from noise. To do it, the transmitter is modulated with an AC signal, often at several kilo-hertz. The receiver is locked with the transmitter, so it is ONLY sensitive to the transmitted signal. The technique is known as the phase sensitive detector, or lock-in amplifier.


Sharp make a good IR ranger finder easy to interface with a PIC microprocessor.

US range several meters

PIR use a commercial one for security lighting they have done all the hard work.

Supermarket doors use ultrasonics if I'm not mistaken.

There are one-point IR detectors for doing that, but the ones HERE aren't too good at detecting soft, light absorbing objects (e.g. people wearing clothes).
(Some of those are range-finders and some give a on/off signal when an object comes within range.

For reliable detection, you may be better off a PIR sensor such as THIS. You can reduce the sensing angle with a tube so it will give a pulse out whenever someone passes through the doorway.