Hello
I’m actually noob
Me and my friend decided to create our first multitouch based on FTIR. Table will be 75cm x100cm size from acrylic sheet (we still don’t know it thickness)
The first question - LED’s characteristic
So I went to the market… And found only two suitable LED’s:
1. LED 5mm, 1W, 850nm, 150 mW/sr., 1.9Vx0.7A, 50 grad - cost 2.77$
2. LED 5mm, 1W, 850nm, 60 mW/sr., 1.9Vx0.7A, 140 grad - cost 2.77$
3. LED 5mm, 1W, 940nm, 35 mW/sr., 1.9Vx0.7A, 140 grad - cost 2.77$
4. LED 4 * 5mm, 850nm, 80 mW/sr., 70/30 град., transparent - cost 3 cent
5. LED 5mm, 940nm, 20 mW/sr., transparent - cost 0.03 cent

If follow the recommendation witch I found on forum, we need to set 1 LED per inch. Designed table perimeter is 138 inches = 138 LED’s. Using first 3 LED’s in the list will be very expensive 138x2.77 = 382$
Is it possible to use LED’s with lower when 100 mW/sr luminosity does it will cause much worst blobs when if if was LED’s with 100+ mW/sr?

Thanks

wow yeah thats too expensive, go with the 80mW/sr but put it all 4 sides, and angle the leds up slightly, to get better results..

Hello Taha, Thanks for reply
We will place LED’s among all sides
Taha, so your proposition in current situation is #4?
“and angle the leds up slightly”
we also want to try make angeled sides of acrylic
What about dustance between LED and acrylic edge?

Thanks

You want to get the LEDs as close to the acrylic as possible.  Some people even drill a small hole for each LED, but I think that is overkill.  You do not need to angle the edges, as long as they are well polished and you angle the LEDs up.

Good Luck!

Thanks xelapond

I suggested angling the leds cause yours were only 80mW/sr , it will make your blobs brighter, you dont need to worry about angling the edge of the acrylic sheet.

It’s me again
Ok, I found IR LED’s of two types, which much better and cheaper
* IR 850nm, Vf(V) Typ.: 1.5, Vf(V) Max.: 1.8, 160 mW/sr., angle: 13° - price per LED 0.308$
* IR 850nm, Vf(V) Typ.: 1.5, Vf(V) Max.: 1.8, 80 mW/sr., angle: 30° - price per LED 0.308$

Please, help to choose one of them, which will be better for our project

Thanks.

Get the 2nd one with 30°, the other angle is too narrow, even 30 degrees is narrow you should have around 40 degrees…

ohh one question is the full angle or half angle.

Suppliers have indicated what this full angle.
Heh… looks like I need keep searching… so be it

I’ll be back as soon as found something
Thanks

so it must be full angle, full angle is the total range the half angle of that led would be +-15 degrees

Taha, when you told about 40 degrees, you mean half angle? Or it was minimum value of full angle which supposed to be?

thats the optimum full angle, you can use the 30 degree full angle it will work just have your leds like 2~5mm away from the edge of the acrylic

hm… interesting… thanks for advice We will try some other ways to find LED’s which will be applied for our project.. If we don’t find better, we will use LED’s which I found before + take into account your advice.

Thank Taha