Forums > MaxMSP

infra-red sensor?

May 9, 2006 | 2:56 pm

Hi,

Sorry if this is a real newbie question, but I need some help figuring out how to use IR sensors.

I need to be able to track the location of a moving object from above. I’m told this can be done using an infra-red beam attached to the moving object, which would be picked up by a sensor mounted overhead. My problem is that I don’t know how to generate an IR beam, nor what kind of sensor would read it.

Any advice?

I’ve done this in the past with a colour video camera above and the moving object wearing a coloured light. But this time, the ambient light levels will be too bright, so I think IR might be the way to go.

Thanks for your help.

Lori



Nat
May 9, 2006 | 4:00 pm

You can still use a camera, however, it will be easier with a camera that has night shot. In addition, you will need to block visible light with a filter (called cold mirror). For the IR source, you can use traditional IR LEDs that are pretty cheap. Even without nightshot, some cameras are very sensitive to IR light, try it with a TV remote.


May 9, 2006 | 4:53 pm

Quote: lbeckste@ryerson.ca wrote on Tue, 09 May 2006 07:56
—————————————————-

> I’ve done this in the past with a colour video camera above and the moving object wearing a coloured light. But this time, the ambient light levels will be too bright, so I think IR might be the way to go.
—————————————————-

As the other post said, you can still use a camera, which I would reccommend. Essentially, you’re just going to be tracking a different color. The advantage of tracking IR is that it is invisible to the eye, so your tracking mechanism won’t be obvious to the viewer.

There is a lot of info on the web about making a cheap IR webcam. Here:

http://homepage.ntlworld.com/geoff.johnson2/IR/

is one example. I think that some people on this forum have done this.

If you know motion tracking with visible light, and you have an IR sensitive camera, the final step is to make sure the thing you want to track has a strong IR emission. You can get IR LED’s, and hook them to a battery. Perhaps a slicker solution would be to get some reflective material and stick it to the thing you want to track. 3M makes some reflective tape that is quite effective. I just stumbled on IR flashlights that might help:

http://www.maxmax.com/aXRayIRLightOrder.asp

Google around a bit more, and the world of IR will be yours.

mzed


May 9, 2006 | 5:04 pm

It’s possible to use a standard webcam as an IR camera, with a little
modification.

I successfully modified a Logitech Quickcam Pro 3000 in about 10 minutes by
following the instructions on this page:

http://homepage.ntlworld.com/geoff.johnson2/IR/

If you want a bright source of IR light you can buy an IR illuminator on
eBay pretty cheaply, they vary in brightness depending on the number of IR
LEDs they contain, usually about 30 – 150 LEDs. You might be able to use a
fixed source pointed at your target if it’s bright enough and the beam isn’t
directly visible to the camera, though I haven’t tried this.

A good source for individual IR LEDs is Junjun Robotics (www.junjun.org). I
bought 10 for $2.50 last week and they arrived today, which was a nice and
quick delivery time for a transatlantic order.


May 9, 2006 | 7:05 pm

Thanks for your responses. Lemme see if I got this straight:

I can use a regular (non-IR) camera but I have to use a cold mirror filter.

Or I can hack a regular web cam to make it IR sensitive.

Or I can get an IR camera.

Question (maybe dumb):
I need to motion track a point source as it moves around. The ambient light levels will be fairly bright (indoors with lots of windows during the day). Will an IR camera (or a hacked one or one using a cold mirror) see everything, or just the IR beam? I need it to just pinpoint the location of the IR beam.

Thanks again for your generous help!

Lori


May 9, 2006 | 11:26 pm

An IR camera will see everything in the infrared spectrum.

Sun, people, warm things, all reflect and/or radiate in this spectrum, but you will make sure that your IR emittor/reflector will be much brighter than any other IR source in the room, making it easy for your software to distinguish it from any other IR source.

If you’re using Jitter, check out the cv.jit objects. Easy to use.

mz


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