Some IR questions- beginner

[jbp26]

Hi, I'll start by saying that I'm totally new to engineering. I studied literature, psychology, and language in college, and for some reason my new job decided to give me all the engineering projects. The last few months have been constant research and experimentation, and I've done ok so far, I've been able to build and fix a lot of basic things. What kills me every time though, is the trouble shooting. Theres so many variables in all of these topics that are completely foreign to me, I really don't know how to approach solving them. Hopefully someone can help me out here, all of these stumbling points become incredibly educational, once I learn whats going on.

The current problem thats been plaguing me has to do with this eye tracking system. It requires a substantial source of IR light to illuminate the subjects eye, so the camera can record the pupil. One thing I've been trying is with glowsticks. I ordered some IR glow sticks, the kind you just snap, shake, and htey light up, just these are infrared. They're usually used by the military in conjunction with nightvision goggles.

So I opened one up and cracked it, and held it by the camera to see how much light it gave off- and the camera registered none. My digital camera and cell camera also registered no light emitting from it. I tried this many times over about 4 hours- nothing.

Any idea what the problem here is? I did some research and found that regular IR light is reflective, whereas thermal IR like this is emitted- could that be a problem in reading it? I called the company, to no avail. All they were able to tell me was the wavelength of the light (850-920nm).

Thanks to everyone for their help.

 

[sreid]

Just a thought; 800 nm is in the near infrared which would be for a pretty hot source, near visable light. An IR camera looking at room temperatures would be in the far infrared,

 

[VEBill]

800nm is near IR (as used with IR Remote Controls). Many consumer camcorders are sensitive to this range (you can see the otherwise-invisible IR from Remote Controls via the camcorder). I'd have assumed that 850-920nm would have been close enough to be same, but I dunno.

The systems that I've seen (on TV - probably Discovery Channel or the like) used obviously-commercial IR illumination systems consisting of banks of IR LEDs. The IR illuminator was a flat plate on a fancy tripod mount, and the plate (coated PCB?) had a cluster of perhaps about 100 IR LEDs. Such illumination would be several orders of magnitude more than a light stick.

With the more recent ultra high-power IR LEDs, you'd better check the safety standards before frying someone's eyeballs. Some newer LEDs are much more powerful than even a few years ago. You might not need a cluster these days, but you'd better be more careful.

A cheap IR-sensitive camcorder and a borrowed IR Remote Control might help with troubleshooting.

 

[IRstuff]

Go to your local electronics store and get a cheap CCTV camera with IR LEDs; they go for about $50-$100. Since they're designed to be sensitive to the near IR from the LEDs, you can use it to verify functionality of your own source as well as potentially substituting for your sensor.

As for the IR glowstick you bought, it's likely that its wavelength is actuall higher than 900 nm, making it less likely to be visible in a normal camera, whose response generally falls rapidly past 800 nm.

The human eye is nominally characterized by response up to 780 nm, but if the source is sufficiently bright or the eye is sufficiently dark-adapted, it can respond beyond 850 nm, which would suggest that something like an IR glowstick that should only be visible to night vision goggles would need emit a wavelength beyond 900 nm.

There's also some apparent misinformation you're getting. Infrared is no different than any other light, there are some things that emit it and there are other things that can sense it. You, sitting at your monitor, are sensing the light emitted from the display. You are also emitting infrared, which could be sensed by the appropriate sensor.

If the source is strong enough, you can sense infrared directly as a heat change. The explosions in the Water World and Backdraft shows at Universal Studio can be be immediately felt as heat impulses on your skin. Some rattlesnakes can sense the thermal emissions of their desired prey.

TTFN

 

[Warpspeed]

IRstuff is definitely on the right track.

To make your CCD camera more sensitive to IR, and less sensitive to visible light, try placing a red filter in front of the camera.

The red acrylic filters commonly used in front of red LED displays is very low cost and readily available. It is also very effective. The front out of an old digital alarm clock would work fine too.

 

[jimkirk]

Another handy trouble-shooting gadget you can get is an IR sensitive fluorescent indicator. Radio Shack used to sell them for less than ten dollars, I don't know if they still do. You had to "charge" it by exposure to bright visible light for a minute or two. Then, for half an hour or so it fluoresces orange in the presence of infrared. Not sure exactly what frequency range they respond to, but I've used them with IR LEDs.

 

[MacGyverS2000]

Interesting... never knew you had to charge those RatShack IR indicators before use.

For a cheap IR filter, develop an unexposed portion of 35mm film.

Dan
Owner

http://www.Hi-TecDesigns.com

 

[VEBill]

Some Sony camcorders have a 'Night Mode' (filter and optional IR illumination). There are even optional more powerful IR illuminators.

Later models had the Night Mode disabled in high brightness conditions (daytime) because some people were using it to see through certain types of fabric (clothing) under some lighting conditions.

 

[e2zn]

How about an IR sensor? About a buck at Mouser:

512-QRE1114

Add battery, resistor, and DMM and you've got it. Cheaper than a camera. The part number above also has an IR diode, so if you need to check the sensor, you can hook up the IR diode to check that the sensor is working.

e2zn

 

[e2zn]

Correction on that PN:

512-QRD1114

Sorry about that...

e2zn