LED Sensing ~ BI-Directional LEDs Part – I

Sunday, 3 May, 2009 § Leave a comment

In my quest to find other methods of input detection for multi-touch and multi-modal hardware i came across another technique made famous by Jeff Han it is the use of LED s as bi-directional sensors. This technique is in no means new, it know fact that LED s can behave in such a way that, they act as sensors, when they are reverse biased. The theory behind how this all works is explained below.

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Let there be light…

Friday, 30 May, 2008 § Leave a comment

When it came time to choose the leds there were only a limited number of choices, and since the most popular on NUIgroup forums is the OSRAM SHF485, I went with that.

A bit of background when picking IR emitters…

For everyone else out there when picking leds dont look at that their power for a measure of their luminosity. But rather look at their radiant intensity, which is measured in mW/sr. Typically radient intensity of 100+ is sufficient for for FTIR, on the other hand for DI you want both luminosity as well as dispersion angle, Osram SHF485’s have a radiant intensity for 160mW/sr.

On a side note, you also need to keep in mind the lens on top of the led it self and the angle IR emmits from the led it self. For FTIR its an narrower beam is prefered of around ±20° and for DI a wider angle beam is prefered ±40°, so if you are creating a DI setup then Osram SHF485P would be the better choice.

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