FTIR Multi-Touch Surface
Matthew Hagerty, Jun 2006 (http://digitalstratum.com)
Work in Progress.
Before spending a $30 or more on LEDs for this project, I decided to buy, and test, about five or so LEDs of various types that I found referneces to from other FTIR projects. Here is the lineup of LEDs I tested:
Five LEDs tested for best FTIR results.
|LED||Rating (1 - 10)||Spec|
|OSRAM SFH485||10||880nm, 1.5V @ 100ma, 160mW/sr, Angle +/- 20|
|OSRAM SFH4502||7||950nm 1.5V @ 100ma, 60mW/sr, Angle +/- 18|
|LUMEX OED-EL-1L2||8||940nm 1.4V @ 100ma, 60mW/sr, Angle +/- 30|
|RADIO SHACK 276-0143||4||940nm, 1.2V @ 100ma, 16mW/sr, Angle +/- 45|
|AGILENT HSDL-4220||9||875nm, 1.5V @ 100ma, 76mW/sr, Angle +/- 30|
The rating is just a number from 1 to 10 that I gave each LED. It is pretty much just a scale of each LED compared to each other. The SFH485 was given a 10 because is was the brightest in my tests, and all the other LEDs were rated by their brightness compared to the SFH485.
I was just about to purchase 30 or 40 of the SFH485 LEDs from Digikey when someone in the #FTIR chat room asked if I wanted to go in on an ebay purchase of 500 LEDs. I looked at the auction and the specs for the LEDs was very favorable, so we took the gamble and got 250 LEDs each for $25 each ($0.10 per LED is pretty good!) The LEDs were apparently designed as an IR light source for use in consumer electronics like cameras and such, so they are good and powerful. Here are the basic specs:
LED870-01UP: 870nm, 1.5V @ 100ma, 90mW/sr, Angle +/- 10.
They really worked out well and you can see by the bright spots on the build page. I may still buy some SFH485's just to see how much better they are compared to these.