The first edition release of the NUI Group community book Multi-Touch Technologies, is here!

This book comprises state of the art articles from the NUI Group Community Wiki, as well as several chapters written by leading experts in the field specifically for this publication. Detailing basic hardware technologies as well as the process of developing software suited for multi-touch systems, this book provides a technical introduction to the world of multi-touch.

I am proud to have been a contributor to and co-author of this book. Please check it out as it is full of helpful information. Well done to all who took part and made this possible..

Click here to download a copy of the book..

For more info please see the original post here at NUIGroup.

UPDATE:

We have gone ahead with the printing process, through Lulu.com’s online printing services. A this point, we are still waiting for an ISBN number to allow distribution through Amazon.com and other retail channels to achieve maximum readership. Once the ISBN application process is completed, ordering information will be made available. Tentatively, the price for a copy of Multi-Touch Technologies is $7.00 USD, + shipping. We are working to lower this cost: it is not final.

And remember, the online pdf is 100% free! – the version that is going to the presses is available on the NUI code downloads, as described above

Thanks!

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 capablities.

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.

Alrite to update from my previous post heres an update video of my 3×2 matrix using led sensing

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.

However this can take a long time since going to logic zero will take time, an easier way to detect input is simply by measure the voltage across it, after you have given it a short time to discharge. What this will give you is capacitive charge held by LED, you can use this to determine whether an input was created or not.The LED is not an ideal device, that is, not all of the discharge is caused by photons, other causes include thermal noise and leakage. So given enough time the charge will decay without any light.

Finally, since LEDs are not designed to be used as light sensors, the light sensing ability varies from LED to LED. There are some types that are better than others.  I’ve found Red LEDs are the best as they will be sensitive to more colours of light where as blue LEDs will be sensitive to only blue light. Worst of all are white and IR LEDs most dont work effectivly to obtain any significant reading. The junction size is also important so the smaller an LED is the more sensitive it will be as the capacitance is smaller and it takes less photons to discharge it. Finally a clear package will let more light in than a coloured one. If you want to use LED light sensors as touch sensors then surface mount LEDs are probably best, since they have a wider FOV and are in a clear package.

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.

It is a little known fact that an LED can be used not only to output light but also to sense it. From a basic electronic standpoint a diode is simply a PN junction, so are light emitting diodes (LEDs) and photo diodes, therefore essentially all diodes are the same thing in that they are a PN junction.

Any semiconductor can be doped with one of two types of impurities (from either group 3 or group 5 in the periodic table)  that result in material that conducts electricity in two different ways. One is with an excess of electrons is called N type and the other with a shortage of electrons is called P type, this varience is due to the nature of the doping element which either create an excess or shortage in electrons. This is because a shortage of electrons can behave, as far as electricity conduction is concerned, just like an excess of positive charges. These positive charges are called holes in recognition of what they are, the absence of an electron. So electricity can be conducted by the flow of holes in P type material or electrons in N type.

So when a P and N type material come together to form a junction some of the holes in the P type materiel move into the N type material where the combine and cancel each other out. Similarly some electrons at the junction move into the P type material and cancel each other out. So around the junction an area of materials builds up that has neither electrons or holes and so will not conduct electricity at all. This is known as in intrinsic region or I type. This seals off the path for the migration of any more holes and electrons and the I region stabilises.

To get electricity to flow you have to apply an external voltage  that adds more electrons to the N side and more holes to the P side. This builds up a potential that is big enough to break through this intrinsic layer. However, if you put a smaller voltage across it you just put an extra charge or electrostatic pulling power across the I-Region.

Now if a single photon (light particle) enters into this I-Region it interacts with an atom and forces it release energy (i.e. it causes the electron to jump into a higher orbit). This frees up an electron for conduction  and it also leaves a hole behind where the electron originally was.

we say we have generated an electron hole pair, that is one electron (free) and one hole. These would normal recombine due to there oppsing nature, but the electric field across the region pulls them apart causing a tiny current to flow. The more photons that enter this light I-Region the more the current adds up and so you have a current that is proportional to the light falling on the diode, this is called a photo current.

Well sorry for the delay in releasing the source of my media viewer application, i got busy with exams and what not… Anyway i promise the source of MediaViewerApp 0.4b should be up by the end of the week.

As for some news I’ve been working on some interesting approaches for multitouch and multimodel input devices…. Currently my work has shifted away some what, from the whole software side of things and moved back into my preferential domain; working with hardware.

I’ve never been a huge fan of either capacitive or optical systems used for input detection… each has there own flaws, which I’m not going to go much into depth describing, apart from just saying they are far from perfect. The major drawback of capacitive systems’, is that they rely on the human touch factor; where the system seizes function if  the users skin does not come into contact with the capacitive input device(i.e. if you are wearing gloves the system seizes to work). Although Optical Systems by far are one of the best methods of detecting input they still rely on field of view (FOV) and as such aren’t as mobile in large form factors, since the depth of the system is proportionally related to size of the screen depending on the focus of the lens being utilized by optical sensor.

As such i’ve moved away from both these methods and have started to look into other electronic methods of input detection.

Well guys im currently in the process of cleaning up the code for my Media Viewer Application Ver:0.4b after that i will be reasing the code under MPL or MIT licence.  So stay tuned

Ok guys this has been a long awaited release… Im currently releasing the alpha version of media viewer application 0.5.  Essentially its the same as older media viewer applications that i’ve released with improvements to the code, the most significant changes that can been seen are the applications capablity of aranging visual data in various patterns, as well as having mp3 playback capablity.

You can Download the application from the Downloads section or from here

Cheers guys

Hey guys sorry about not uploading the application. I’ve been busy with university and the lack of a fully functioning table has taken some to develop the application as well… So what im asking rite now is a few beta testers that would be willing to help test the application and let me know how well its working and what are the major bugs that appear. All i need are people with working hardware, and not testing via simulator or ipod/ipohone.

Thanks guys.