RIR Sensor with ~3ft detection capability?

[NickF]

Question for you sensor experts...

I'm looking to do a project that would involve detecting when an item passes through a doorway near ground level (~6 inches above ground level). Doing a bit of research it looks like a reflective infrared sensor would do the trick ... only issue I have come across is that there seem to be a slew of these sensors with detection capability of about 15mm max and then another class of these (home security grade) that have detection capability for several 10's of feet.

Any ideas on a RIR sensor (links appreciated!) that has capability ~2-3 feet? Another caveat is I'd like to string up multiple of these sensors in a close proximity, each with the sensor observing a 2-3 ft area right in front of it.

Thanks!
Nick

 

[Tony Stewart]

It may depend on your unwritten assumptions.
Size of object, minimum/max reflectivity, object motion direction? doorway distance, immunity ? error rate allowed?

I have designed / built transmissive IR LED sensors for 1~2m range with a sensitivity of 1mm at 1m/s

 

[MikeMl]

Can you put a retro-reflector on the object being detected, or how reflective is the object at IR?
Can you put a retro-reflector on the far side of the door jamb, and use it like a beam-break detector?

I have had great success with garage-door safety beam sensors... Cheap, long range, works in high ambient illumination. Requires a simple interface circuit. Write back if you want more info...

 

[Reloadron]

I agree with Mike as to safety sensors. A Google of Garage Door Safety Sensor will get you dozens of reasonably priced sensors.

Ron

 

[AnalogKid]

That 10 ' range is a maximum, not a minimum. They will work over much shorter distances. Too short, and reflected energy from whatever is surrounding the reflector might go around the object, or the main beam can reflect directly off the object, and hit the receiver with a detectable energy level even when an object is blocking the main path.

ak