Loooong distance IR detection, and IR collimation

 · 2006-05-10T14:18:01+00:00

Hi,Every body know about the IR remote controls that we use everyday for our TV, music set etc. They are short range, almost omni direction (due to reflections from almost any surface) controllers.Imagine that we have a tube/pipe of some sort with radius R, and lenth L. We have positioned the IR transmiter at the end of this tube and alligned it in such a way that its illimunation axis parallel to the tube so that the IR source can only be visible if the observer/receiver aligned with the tube/pipe. BUT the inner surface of the pipe/tube must be coating with an IR absorbing material so that the tube will not act as a wave guide. Or the tube/pipe must be made out of an IR absorbing material.Do you know any IR absorbing material?Is it possible to collimate the IR light source with the above mentioned method to 2degrees? OR is there a way of creating very narrow IR light cone ie. collimation around 2degree?If we use an ordinary IR remote control receiver (or some other low-cost IR sensor) to detected the IR light about 100 meters away from the collimated IR source how much IR power (how many IR LEDs or what else) we need?ThanksRico Maxle

May 10, 2006 21 Replies

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Rich Grise 20 years ago

Well, an "Opticon", in this context, to the best of my knowledge, is a photocell (electric eye) mounted up on the stoplight bracket, and ambulances and fire trucks (and, presumably, the cops) have some secret code that they flash through their windshield with a strobe - the Opticon picks up that signal, and changes the cross-lights to red, and changes the light for the emergency vehicle green. Some guy had decoded that code, and was breezing through town, but presumably got caught because the red-light cameras were timed to the moment when the light was _supposed_ to have turned red - there was this car in the intersection, and the "switch to red" signal had been overridden!

They caught the guy. :-)

Cheers! Rich

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zwsdotcom 20 years ago

The answer to this is "it depends". Some use coils embedded under the road (often used at highway on-ramps in Long Island, for instance).

The more modern scheme is a camera in the traffic light that exploits the highly reflective license plate on a car to detect if the intersection is occupied.

I read something - here maybe - about a motorcyclist who was tired of not triggering this type of detector. He put a strip of orange reflector tape on his helmet and all was well.

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