Hi all,

I’m a student from the netherlands and start building a FITR multitouch display. Now i’ve already a set up working with one plexiglass surface and white sketch paper (polyester) . The feedback of the infrared light is OK. Now i have one other plexiglass with matte white foil (window foil) on it (so beamer projection is much closer your finger). Now when i use this surface, the feedback of the infrared light is really bad. (see attachement) You can see the infrared LEDS but the blobs are not bright enough.

The difference between the two set ups is that the one with the foil is attached to the plexiglass, the other set up has white sketch paper that is not attached.

Can anybody tell me why the blob feedback is not bright enough? It must be something to do with the foil, or maybe the LEDS are not good enough?

LEDs specification: http://www.leds-buy.nl/led-850nm-graden-5mm-p-106.html

Hope to see a reply.

Grz,

j00

Hi!
i think you need a compliant surface. Maybe “roll-on vellum” technique may help you.

Pole

Hi j00,

I´m from germany and i tried it with a window foil, too. Same bad results. You really need a compliant surface like a thin tier of silicon. I tried it this afternoon with tinkerman´s roll on technique, but my silicon which i bought at the hardwarestore didn´t solve in the acetone :-(
I´m calling a company which produces glue tomorrow to find out what else I can take.

Hope I could help a little bit.

Tom

Hi,

Thx guys for your reply.

@Tom;
To bad it didn’t work! Maybe the new glue will have a better result? Let me know if it works…
I didn’t try the compliant surface yet. The plexiglass with the sketch paper works fine, but i don’t like the distance between finger and the beam image, that is why i’ve tried the window foil. Well to bad.
Tomorrow i will replace the LEDs with the Osrams 485’s but i don’t think i will recieve a better result.

FYI: I’ve tried some silicon spray (fluid), spread it on the whole surface, the surface was very smooth (predictable), but the next day the finger blows were brighter! Only problem is that it is not constant…

grz,
j00

Tom_S - 22 July 2008 01:35 PM

Hi j00,

I´m from germany and i tried it with a window foil, too. Same bad results. You really need a compliant surface like a thin tier of silicon. I tried it this afternoon with tinkerman´s roll on technique, but my silicon which i bought at the hardwarestore didn´t solve in the acetone :-(
I´m calling a company which produces glue tomorrow to find out what else I can take.

Hope I could help a little bit.

Tom

Hi guys you can use regular lacquer thinner or panit thinner… it usually does the trick, acetone will break the bonds of silicone, and from my tests i’ve found that if you use clear silicone it works better than compared to white silicone which turns clear as it dries.