Linked by Thom Holwerda on Tue 10th Jul 2012 01:24 UTC
Microsoft "Microsoft and Perceptive Pixel Inc. (PPI) today announced that they have entered into a definitive agreement under which Microsoft will acquire PPI, a recognized leader in research, development and production of large-scale, multi-touch display solutions." Yes, Jeff Han is now a Microsoft employee. This demo still amazes me - from 2006. Before the iPhone. Before Android. Before the iPad. Remember that the next time you wind up in a discussion about who supposedly invented what.
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RE[4]: I built one too!
by Laurence on Wed 11th Jul 2012 09:57 UTC in reply to "RE[3]: I built one too!"
Member since:

Outside noise is not necessarily that much of an issue. If you stick the piezos inside of the device's casing, they will be far, far more sensitive to finger tapping and friction on the device's casing than to outside noise, since there's a lot of acoustic reflection going on at the air-casing interface. That, and acoustic power decreases as the square of the distance that is travelled from the source. To see how big the difference is, just gently tap the surface of a microphone when recording sound : you should get a peak that is far more intense than anything you were recording, even for a very gentle tap.

Pockets are indeed an issue, but on this front microphones are just as bad as capacitive touchscreens, which will also run amok if you forget to turn off your phone before putting it in your pocket. One specific pitfall of acoustic sensing is friction on the back or the sides of the device during device use though. Accounting for these could indeed require complex noise cancellation systems.

I understand the acoustics of it all (I've spent a lot of time working with mics as well). While I appreciate that outside noises isn't a huge issue most of the time, it will be an issue some of the time. For example, in night clubs where the sound system is well tuned for punchy kick drums. Such a touch pad under those conditions could be worse than useless.

You also then have to account for the amplitude of the sound (depending upon how heavy handed the user is), the different refractive properties of the casing for each unique phone handset and the subtle differences in the tune of the touch depending upon the make up of the casing (crude example: tapping a metal table produces a different sound to tapping a plastic table).

So I just think the amount of code that would have to go into understanding the difference between sounds originating from physical contact and those from external sources could amount to a more complex solution than having sensors detect physical contact via the resistance of the users finger. Though I will grant you that some of the above can be configured at run time by a control panel-type app - but even then, that means you don't have an "out of the box" solution unlike with the current method.

Further more, attaching a new phone case (eg rubber sleeve or patterned cover) would then also change the acoustics and thus potentially break the touch pad. Which would be a terrible step backwards in terms of usability.

Don't get me wrong, I think the mic'ed method is a fascinating idea and it sounds like great fun for a lab / home environment. I just think it's not better (or even practical) than current capacitive inputs.

Reply Parent Score: 2

RE[5]: I built one too!
by Neolander on Wed 11th Jul 2012 20:27 in reply to "RE[4]: I built one too!"
Neolander Member since:

Regarding night clubs, I don't know if that would be enough to perturbate an acoustic touchscreen, but I agree that doing the experiment with a prototype would be a good idea...

I think that tap amplitude and tune are not very important for this design, however, as long as the following conditions can be met :
1/It can be assumed that the acoustic properties of the screen are uniform and there are some absorbers on the sides to address the problem of reflections
2/It is still possible for the mics to detect a reproducible signal that is reasonably far above the noise level

That is because, for the design which I have seen at least, finger position tracking is based on sound propagation delays, not attenuation or wave shape. If we detect a pulse on mic 1 at a time t1, on mic 2 at time t2, and on mic 3 at time t3, we can measure t2-t1 and t3-t1, then deduce spatial positioning information using such calbration data as the speed of sound inside of the screen material and the well-known mic network geometry.

I would gladly draw you a sketch that explains this in more details, but my main computer is currently undergoing repairs and cellphones are not very good for that kind of things.

Since we are only interested in the direct signal flowing from the impact region to the mics without undergoing reflections, rubber casing should not be a problem. In fact, they could even help addressing the problem of reflections and the one of friction on the back and the sides of devices that I mentioned above.

To conclude, I am not sure that acoustic touchscreens could play the same role as capacitive touchscreens either. The guys who worked on them at that lab preferred to market them as a path towards cheap large touchscreens (such as touch-sensitive shopwindows). I was just playing with the idea in thoughts experiments to see what would be the advantages and drawbacks, and found that it might work surprisingly well in that scenario, with much simpler hardware than the capacitive electrode mesh insanity. But I'd probably need to build a prototype (which is way beyond my knowledge of embedded electronics) in order to test some of the potential issues that have been raised here.

Edited 2012-07-11 20:43 UTC

Reply Parent Score: 1

RE[6]: I built one too!
by Alfman on Wed 11th Jul 2012 21:14 in reply to "RE[5]: I built one too!"
Alfman Member since:


Do you think acoustic reflection is that big a deal for software to handle in your model?

Granted, I don't know how much attenuation to expect, but I'd be surprised if it's difficult to differentiate between the primary and reflected signals. My guess is that secondary waves would loose high frequency components far more quickly than low frequency components.

Instead of trying to absorb/eliminate reflections, we may be able to use the information from reflections to our advantage. Consider a sensor on the right hand side of the table that picks up a pulse, shortly followed by one on the left hand side. Ordinarily the algorithm would measure the time lapse difference and register a corresponding touch on the right side. However the pulses may have been triggered by environmental sources off the table.

If the reflection isn't too week, we might be able to prove that the pulse originated on the table because from anywhere else the timing of reflections would be off.

Instead of attempting to write an explicit algorithm for this, it might be easier to use a generic pattern matching algorithm and perform a hough transform across it. This would produce a 2d graphic with intensities corresponding to the areas that have the strongest matches. This could be projected onto the table so that it gets lit up in the spots where it is touched. Then try to fool it with external noise.

Edited 2012-07-11 21:19 UTC

Reply Parent Score: 2

RE[6]: I built one too!
by Laurence on Wed 11th Jul 2012 22:34 in reply to "RE[5]: I built one too!"
Laurence Member since:

I follow what you're saying so no diagram is required (thanks for the offer though).

Actually, you've raised some interesting points there - to the point of nearly convincing me (it's a real pity I can't up vote once I've posted).

I don't think there's necessarily a "right" or "wrong" answer though, at least not without building a prototype and testing it (sadly it's above my level too). I do think you're right about the huge potential of using such a solution for larger surfaces though (if it's not already in wide-spread use).

Reply Parent Score: 2