FreeTrack Forum

Hi!

I want to use freetrack with a reflective sphere headset clip.

I'll be sitting up to 1 meter / 3 feet away from the camera, with a fluorescent lamp high above me and completely out of the frame and a blank white wall behind me, so I hope background noise won't be a problem.

I'll need to build a LED array and a reflective clip, and I'll appreciate it if you give me some pointers. I have about 0 knowledge in electronics but I'm a quick learner :]

How many LEDs will I need in the array?

These can be normal IR leds, not necessarily wide angle, right?

Does the shape of the array matter? It seems that many users make a nice round array built around the webcam. Would a simple rectangular array positioned next to the webcam be ok? It would sure be easier to build and maintain.

How do I figure out the power supply I'm going to need for my array?

Where can I get reflective tape? Is it something which should be available at an electronics shop? What size of spheres should I use?

Whoa, that's a lot of questions. Sorry if they've been answered before, I did search but must have missed it.

Thanks in advance,
Twister.

I don't have any experience with the reflective approach to the FreeTrack system.  I imagine it is hard to describe a good generic system since there are so many variables... e.g. the brightness of the led's the sensitivty of the camera, the quality of the reflective tape.  However, it would be good to see someone describe a detailed set-up that uses commonly available supplies, such as those from Radio Shack.

But, I do have some useful information to add.  I've been experiementing with reflective tape for another purpose (navigation for a Roomba floor vacuum).  I've found that there is a lot of variation in the quality of reflective tape. The best I've seen so far is the white reflective tape I purchased from WalMart.

I can't find it on their web site, so it may be a local thing only. But, I found it in their automotive department.

Regarding spheres.  I suspect that you can just get by with a round circle of the reflective tape... perhaps 1/4" diameter.  Now there are existing round reflective plastic things.  But, I didn't experiement with them becuase the "grain" of the reflective prisms is too large for my Roomba navigation system. But, they  may be good for the FreeTrack.  However, the size may still be too large since they seem to start at about 1/2" diameter.

Making a sphere will be much more difficult.  I think the only way is to get some wood beads, and then use reflective paint.  But, buying this type of paint will be much more difficult than buying tape.  I don't know where you can find the paint.  Also, the best reflective "paint" really is a 2-step process.  You apply a base coat of an adhesive type paint, and then cover it with these tiny reflective beads that look a bit like sand.

I have seen a reflective spray paint by Rustoleum.  But, I have doubt about how much light it reflects in comparison to the tape.

Regarding the ring of LED's.  Reflective items are designed to reflect the light from a source back to the source.  So an ideal retro-reflector (like the ones placed on the Moon by the Apollo astronaughts) do a very good job of reflecting back to the source.  But, the lower quality ones will tend to spread the reflected light back with a greater spread of light.

So, a ring is a benefit to only the high quality reflectors.  But, a short linear array, like 3 or 4 inches will probably be OK in your situation as long as it is immediately adjacent to the camera.

Joe Dunfee

Thanks a million!

I've seen a reflective clip on the sticky thread, which used rounded sourfaces (half circles) instead of spheres, so it might not be too much of a problem. I'll probably try that with some M3 reflective tape from eBay.

I still need to figure out the LED array though. I'm thinking I'll start with 8 IR LEDs in two rows right beside an unmodded webcam and see how it goes. Can I use 1.5v AA batteries or do I need 9v ? I don't have specs on the IR LEDs from my local electronics store yet, but I'll appreciate if anyone could tell me if I'm in the right direction on the size and type of array and what specs I should be looking for.

Twister @ 20/09/2008 - 15h45 a dit:

Thanks a million!

I've seen a reflective clip on the sticky thread, which used rounded sourfaces (half circles) instead of spheres, so it might not be too much of a problem. I'll probably try that with some M3 reflective tape from eBay.

I still need to figure out the LED array though. I'm thinking I'll start with 8 IR LEDs in two rows right beside an unmodded webcam and see how it goes. Can I use 1.5v AA batteries or do I need 9v ? I don't have specs on the IR LEDs from my local electronics store yet, but I'll appreciate if anyone could tell me if I'm in the right direction on the size and type of array and what specs I should be looking for.

Any luck?? Did this work?

Twister, the voltage of the batteries is just part of the equation of figuring out what you need.  Also, since you will be putting out more light, you will be consuming a larger quantity of electricity.  Regardless of the voltage or LED current, consider going with either larger sized batteries (C or D size).  An alternative is to go with a wall adapter or perhaps using a USB port from a powered hub.

Also, from your post, it seems like you may not be familiar with the idea that the voltages in batteries can be added up as they are connected in series. In other words, the voltage from one 9volt battery is the same voltage as you get from 6 AA batteries.  Though, the 6 AA batteries will last longer, since there is more of the battery there to do the work (assuming both batteries are the same type of chemistry).  You may be interested that if you take apart a 9v battery, you will see 6 AAA sized ones inside.

The amount of light coming out of a LED is measured in mcd = "milli-candles". So, at least you can compare from one LED for sale to another one.  But, how much IR light you need is an unknown. It depends on how far from the light source you are, plus the other factors I've mentioned. What others have done and have working, in situations similar to your own, is the best guide.

One way to approach this issue is to just make it and see if it works. You can add additional banks of LED's in parallel if needed.

Joe Dunfee