Bi-Directional LED Sensing Tips

Friday, 22 May, 2009 § 10 Comments

Okay since my last post i’ve been doing a bit of reading and doing some tests on bi-directional led sensing. These are a some Tips i present to people who are interested in taking this further. I personally have given up perusing this route of sensing mainly due to its limitations of use, and sensing capabilities.

Helpful Hints

Helpful Hint #1: Using Inexpensive LEDs as Optical Sensors

Most LEDs can be used as detectors without harming the device in any manner, there are some leds which dont work as well, the ideal typle of led is a red led and with a clear casing.

The trick to get an led to sense is to electrically bias the LED in the proper current-voltage (I-V) quadrant for operation as a detector and to detect an appropriate range of wavelengths.

The LED, as the name (Light Emitting Diode) implies, is electrically a diode and can be used as a detection device similar to a photodiode.

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LED Sensing ~ Bi-Directional LEDs – Part 2

Sunday, 3 May, 2009 § Leave a comment

So to continue on with my last post … Now that we have this photo current what can we do with it, how can we make use of it, to detect inputs. The nature the LED is such that the photo current is very small, due to the geometry of the PN junction, which is not designed to maximise to act as a photo diode. However using a small trick we can integrate all photo currents over a set period of time, and make the diode act as a capacitor.  We  this by charging up the diode  and then seeing how long it takes the photo current to discharge and go to a logic zero.

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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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Past 2 Months – CityScape 2008 Duabi

Wednesday, 5 November, 2008 § 7 Comments

Well during the past 2 months i’ve been working with as a consultant at a  local Canadian company, Globacore, and with them i was involved in the process of creating a 10m x 1.5m Multitouch wall. My Job entailed designing of the hardware and creating some of the underlying multi-touch software.

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A brief Comparison Between Xbox360 Vision Cam Vs Philips SPC900NC

Monday, 1 September, 2008 § 2 Comments

On the surface at first the the xbox360 cam looks great and works well in an MT scenario, it by far has the best IR sensitive CCD chip on borad, and performs extremely well in MT scenarios when used at 320×240 resolution, you can easily achieve 50+ fps. However where the camera lacks is in its 640×480 resolution range it barely does 17fps, usually it satys between 11~15fps and with that the cpu usage also skyrockets. « Read the rest of this entry »

Quick Update

Sunday, 3 August, 2008 § 3 Comments

Hey guys i thought it was time that i showcased my low FTIR project since its nearly done, here are some pictures of my setup during the construction process, and its current state, a little information about it…

Windows XP Pro SP3
Intel Core 2 T7200 2Gb RAM (IBM T60 ThinkPad)
ATI Mobility Radeon X1400 512mb
Microsoft XBox360 Live Vision Camera

Acrylic Surface, 80x60x0.8cm (31″x24″x0.32″)
IR Frame using U Channels
120 OSRAM SHF485

Toshiba TLP-651U (running at 1600×1200)

Box Dimensions, 90x90x65cm (WxLxH)

Well its time for pictures then…

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BandPass Filter Lens Attachment

Thursday, 3 July, 2008 § 3 Comments

Well recently i’ve had a lot of requests on how i’ve attached my BP filter to my camera… so i thought i might as well post a write up…

Note: in the pitures i’m using the original focus lens that came with the camera but this method could also be employed with a wide angel lens or a fisheye lens. Also it this technique can employed with any camera that has a manual focus lens. For fisheye or wide angle lens your bandpass filter need to be at least 30mm in diameter.

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