Has anyone had any problems with the 10mw 780nm lasers being incredibly dim (yes, I know you can’t see them)?  I have a firefly MV and can just barely see the laser with line filter in, and I can see some visible light from it so I know it is sharply focused.  Do I need to upgrade to 25mw to get a nice strong beam?  The 6mm lens that comes with the MV doesn’t have an IR filter on it, does it?

Parker

The idea of pulsing the laser for safety reasons sounds very appealing. Can I use any laser if I want to pulse it so that it stays open for a couple of milli-seconds 60 times per second? Can anyone tell me what typical rise times of lasers are, do we need to consider them when we want it to shine for a few milliseconds at a time?

Regards
Jerome

You guys might want to look into how green lasers work… they are in fact infared lasers with a frequency doubling crystal to slow the light down and make it appear green.

You can buy green laser pens quite cheap and should be able to remove the frequency doubling crystal and be left with a high power infrared laser that is battery powered and can be used for prototyping right away.

the raw infrared frequency is really high however (1064nm) so it may not be compatible with some cameras.

Just a thought…

So I’ve been researching this topic in hopes of creating a university research team for MT in education applications. Since costs are a big issue, I am trying to see how to get the best performance for the buck (not unlike everyone else here).

So my idea was using a laser setup like AlexP’s multitouch pads. However, I noticed that the surface itself is one plane and the laser is faced up. Would it make any difference if one adds reflective strips on the same layer as the lasers. The attachment under might make better sense.

I’m not sure exactly how weak the laser is according to distance but I thought this could be a better solution for better performance than purchasing two laser.

let´s repeat some posts: (and I hope I am right (and my experience/tests), if not - please response)

AlexP - 03 July 2008 08:31 PM

justin - 03 July 2008 05:17 PM

I think some people think you need to wear the safety glasses all the time. Even when your done tuning the display. When your using it after you built it.

I’m not an expert in this by any means, but consider this:

- Under DI method, hundreds of IR LEDs shine directly in the user’s eye all the time.
- Under LLP (and FTIR) method the IR light shines only when there is a touch and this reflected light is not directed towards the user’s eye but in the opposite direction (towards the camera). According to the Class 3B specs, unless you touch the surface with an extreme reflective object, the use without the glasses should be safe.

~Alex

so for a LLP setup it might be good to avoid reflective materials under/inside your table.
But what if you want to detect objects (maybe mobile phones - many phonecovers are reflecting) ?

780nm 10mW or 780nm 5mW / 850nm at 5mW or 850nm at 10mW ??

-> 780 or 850 : might be important for some cams for a good and easy recognation, but in general both are IR-Lasers and they work

-> 5mW or 10mW or higher : (using of 2 lasers for a clear/good detection (no shadows) recommended - see attached picture)
for smaller tables (~22” +-) 5mW Laser should be sufficient. (you are using 2 Lasers with 5mW in your setup)
for larger setups I recommend to use at least 10mW or more (for big walls)

-> for a good daylight-functionality you may need more (current setup +1), but I don´t know it (havn´t tested)

90° or 120° :
I am using 90° modules because I want to have the IR-light on my screen and not aside, but with the disadvantage having less quality on the screen edges.
120°: best quality of ir-lightning on the surface but with the safty disadvantage to have ir-laser-light at areas where he can aim your eyes(if you don´t have a frame/absorberframe around your screen/surface).

it would be nice if you also post some experiences (if you havn´t done yet) to help finding the optimal laser for the current setup and to prevent safty aspekts.

using more Power as requiered isn´t perfect! (and mostly also not safe!

AlexP.  Do you have any more of your IR lasers around that I can purchase from you?  I want to use them for a LLP setup

SURFACE TRACKER RELEASED !

I wanted to let you know that we just released our Surface Tracker application. It is an open source application for low latency multi-touch finger tracking using OptiTrack cameras. It was designed initially for our Multi-Touch Everywhere system (MUTE), but it should be working more generally as well to track fingers which have been illuminated using the laser light plane method. It might work also for other illumination methods but that’s something that should be tested. It only supports low latency OptiTrack cameras; these cameras have a frame rate of up to 100 frames per second, but due to their onboard image processing, these cameras consume much less computer’s CPU than regular cameras.

The Surface Tracker is a standalone application, which sends TUIO messages to any connected client application at a user defineable IP address and port.

The Surface Tracker is currently only available on Windows. This is due to the fact that the driver for OptiTrack camera’s is currently only available for this platform. We are, however, having discussions with the makers of the OptiTrack camera about extending support of their cameras to OS-X.

To download the Surface Tracker: http://www.future-instruments.net/fr/download.html

For more info on OptiTrack cameras: http://www.naturalpoint.com/optitrack/products/camera-comparison.html

EL