Open Source Interface

Official IR Laser Discussion Thread

2008-06-14T14:54:17-05:00

OK, maybe ‘official’ was a bit pretentious, but this is a very hot topic right now, let’s see if we can pool our collective knowledge on this subject in an easily findable unique thread.

AlexP started the ball rolling with his work with a single laser and a cylindrical lens (taken, I believe, from a Craftsman laser level). Straight from the horse’s mouth:

The lasers that I use are all custom made.

Hese are the specs:

- 850nm laser diode with 10mW (max power)
- Laser diode power supply circuit (photo-diode feedback LD current control)
- Focusable line with 120° spread using a special non-linear lens (even brightness)
- Variable voltage supply 3.5V-5V

I had a bunch of these modules prefabricated for me, and I have some extra.
If anyone of you is interested, you can have them for $95/each.

~Alex

Other threads have mentioned using IR lasers from either a CD-Rom drive or DVD burner drive (I think). I personally have not seen this done yet, but I’m very interested in doing so.

The laser beams must (?) be put through a dispersing lens, which may be as simple as putting a glass cylinder in from of the laser. Anyway, I think the main 2 topics of inquiry right now that I’ve seen from people are:

1. How can one pursue this technique cheaply? Do CD/DVD IR lasers provide enough coverage and power to give consistent results?
2. Where can one find the cylindrical lens? May already be an answer with the laser level idea, but if anyone has a better idea go for it.

Infrared LED Ribbon Help

2008-09-03T10:23:54-05:00

I purched some in frared LED ribbions which were recomended but my camera is not picking them up unless Im shining them directly on the plexi glass and as well when I do that they barely stand out from the other light.... any suggetsions my IF LEDs are (940nm)

Am I going too far with 400 LEDs?

2008-09-02T12:26:50-05:00

I am planing to use 400 LEDs for a 100cm by 64cm but they are not the best this is the spec:

# Item condition: Brand New and in High Quality.
# size: 5mm.
# View Angle: 15-30 degree.
# Voltage: 1.5V-1.6V.
# Current: 60mA-120mA.
# Wavelength: 850nm.
# Lens Colour: Water Clear.
# Emitted: Infrared light

I also would like to know whether drilling 5 mm holes the dept of the LEDs would work as a way of securely mounting them and whether i would need a margin for these.

Easy FTIR - Infrared LED Ribbons

2008-08-08T20:19:03-05:00

We’ve been learning a lot from the NUI Group, so we thought we’d give back a little by sharing a new technique: getting multi-touch blobs from infrared LED ribbons. We first tried to solder our own IR LED circuits. Although we got it to work, it was challenging, time consuming, and created many potential points of failure.

Because I was doing some other research involving lighting, I was familiar with flexible LED ribbons, and had a few of these ribbons/reels on hand in the visible light spectrum. We saw that many people were testing their blobs in IR right away, but that often required a dark room, an IR camera, etc. If you’re just trying to test the quality of your surface, this complicates the situation, as poor blobs could be the result of the camera, stray IR Light, the software, etc. So what we did was wrap one of the visible white light LED ribbons around the acrylic to see the FTIR effect first-hand, with our own eyes. By testing for blobs with visible light, you isolate the effects of the surface, can quickly see the results of different techniques (silicone of various types/thickness, Sulky Solvy, etc.) Not to mention it’s pretty cool to witness FTIR with your own eyes and watch your fingertips glow

We were getting really good blobs with the white light LED ribbons, so we started to hunt around for LED ribbons in the infrared spectrum. We didn’t find a source online, but we had a contact at EnvironmentalLights.com from my prior lighting work. We spoke with him, convinced him of the value it would bring to the multi-touch field, and he actually created a new product for us: Infrared LED Ribbons. You can buy these by the foot or by the reel, and a bunch of accessories are available: wire connectors, power supplies and cables, aluminum channels, spacers, etc.

We did a quick test of the infrared LED ribbon, and it produced some really good blobs with direct touch of your fingertips. It also generated good blobs with test sheets of silicone and Sulky Solvy with a Rosco Grey screen on top. What’s great about the ribbon is that there are so many LEDs surrounding the acrylic, that it’s pretty much completely flooded with IR light, even if the sides are not super clear. And it saves so much time.

Earlier this week, we built our first multi-touch display using infrared LED ribbons, which worked quite well. We used a polished piece of acrylic from TAP Plastics, and an L-shaped strip of infrared LED ribbon with a soldered plug that attached to our power supply. This was placed inside aluminum channels (specifically sized for the LED ribbons) that were cut in the shape of a frame, with neoprene spacers to keep the LED lights the right distance away from the acrylic. We used Sulky Solvy for the compliant surface and Rosco Grey for the screen. Both of these were stretched over the acrylic to make them taught, and affixed using a perimeter of thin double-sided tape. Our IR camera was a modified Xbox Live camera, and we borrowed an Infocus DLP projector for this test.

Our next steps are to work on the housing that will hold the display, find a permanent projector, and start testing our blobs with the touchlib software. We’re using Macs, and ran into a few snags with touchlib on that platform. But we plan to make some tweaks to that (or maybe the new Mac tracker will be ready by then, fingers crossed!) Our ultimate goal is to investigate and document the human factors and usability of multi-touch interaction, which we’ll continue to share with the NUI Group community.

what do you mount your LEDs on?

2008-08-29T18:33:26-05:00

The title says it all

what do you mount your LEDs on?

I found some links to prototype breadboards online, but they usually force LEDs to be spaced too much (1.4") ... they also have weird widths (6.5”, etc) and I don’t know if I can cut them shorter, to make sure I cover the whole lengths.

I know many of you use the aluminium frames also used to sandwich the layers and acrylic togethe, but in my case I am not using an aluminium frame for this.

The area I want to light up is 36” x 23” (Acrylic is 1/2")

What do you think?
Product names + pictures of your LED strips would be awesome!!

Thanks

Buying IR LEDs

2008-07-31T16:14:45-05:00

I’m in the US and looking to buy some 940nm LEDs for my DI setup. I’m having a hard time locating a good place to buy. I’ve found this site… has anyone shopped from here? I figure i’ll use about 80 LEDs in my setup. RadioShack has some but I think $1.99 per LED is outrageously overpriced.

http://www.besthongkong.com/product_info.php?products_id=105

online LED calculators, resistors, and how to find them

2008-08-29T21:11:45-05:00

I am in the middle of planning my MT FTIR coffee table (if I can master the mirror technique to keep it low )

Thanks to everyone who has helped me so far with my questions

I am looking into my LED wiring diagram.
I plan for 1 LED per inch, all 4 sides.
36” x 23” surface = 118 LEDs
I round it up to 120 LEDs (SFH 485)

(updated fixed link)
See: http://ledcalculator.net/default.aspx?values=12,1.5,100,120,0

I like what I am seeing, and understand how I will build this…
BUT where do you find the 1 ohms 1/8 watt resistors the calculator calls for?

Also… would you suggest a DIFFERENT wiring diagram?

This is my first time using resistors

DI Illumination, incandescent with lower voltage

2008-07-06T14:02:44-05:00

Since incandescent light puts out a lot of infrared light, I was thinking of trying to diffuse the light to use that as my infrared source. While researching, I came across an article on How Things Work discussing the merits of running light bulbs at lower voltages then they are rated:

...incandescent bulbs become much less energy efficient as you lower their filament temperatures. The light emitted by the filament is thermal radiation and its color spectrum and brightness depend almost exclusively on its temperature.

(context here, about a quarter way down)

The article states that lowering the voltage of a light bulb will make it last longer, but put out lower quality light, so it’s a bad way to save energy.

So I was wondering if I could get good even illumination with a regular light bulb by lowering the voltage to the point where it produces no visible light, then diffusing it. Has any one tried this or have any thoughts on how this would compare to other methods? I’m out of town but I will post results here.

Obviously this won’t be as efficient as LED’s, but it might make it easier for other people to build tables.

FTIR: SFH485 or SFH485P?

2007-12-18T16:12:12-05:00

At first, I was inclined to go for the “P” version for two main reasons:
1) Better coupling with the acrylic sides cause of the flat head, allowing for a more robust and neat design.
2) Twice as wide half-angle, which in theory would spread out the rays more evenly inside the acrylic.

But then, I saw some people raising attention to the “radiant intensity” spec as being of high importance for the brilliance of blobs. Then I went back and compared the specs for the “P” and “P-less” versions, and what I found was this:

- SFH485
Radiant intensity (If = 100 mA, tp = 20 ms): 25 (Ie min) - 160 (Ie max) mW/Sr
Radiant intensity (If = 1 A, tp = 100 μs): 300 (Ie typ) mW/Sr

- SFH485P
Radiant intensity (If = 100 mA, tp = 20 ms): 3.15 (Ie min) - 6.3 (Ie max) mW/Sr
Radiant intensity (If = 1 A, tp = 100 μs): 48 (Ie typ) mW/Sr

I really have no idea on what all these letters mean, but it’s quite clear that the numbers of the “P-less” version look better. Would it be because of the wider half angle, or even the flat head of the “P”? Does it make the 485P an inferior led for FTIR?

The thing is I have to import this component, bringing its costs way up cause of delivery and import taxes. So I’d rather not risk making the wrong choice. Tks.

The best IR-LED for an FTIR setup?

2008-08-25T10:25:34-05:00

Hi guys,
Iam living in germany and iam planning on building an FTIR setup for me
but now iam all confused what LED i should use ...
I have this one store where we buy often electric stuff from (http://www.reichelt.de) so i actually don’t have to pay any shipping costs which is good because i wanted to start with an beginner-FTIR-setup.

The size of the Touch-table will be aproxametly be about 40 x 30 cm =)
I was not planning on using a projector at the beginning because i don’t have one which i can use for it =P
But maybe later but then iam gonna build a bigger one (probably)

So please take a look at the POLL i did above to help me choose which LED i should use.
if you would take another one write it to me or leave a comment on here, just thought if i buy them at the store i don’t need to pay any shipping cost.

Thanks alot,
Simon P. ,Germany