Building a Pressure-Sensitive, Multi-Point TouchScreen? 31
sonamchauhan asks: "I'd like advice on building (yes, building) my own low-res touchscreen. The reasons for 'build' instead of 'buy' are: 1) to have it sense pressure (pressure sensing is quite expensive) and 2) to have it sense multiple points of contact simultaneously (which is a useful thing). Back in 1985, researchers at U.Toronto built (PDF file) a touch-tablet (not a touch-screen) that fulfilled both requirements (pressure-sensitive and multi-touch) and used only basic electronics: lots of diodes, A/D convertors, etc. Some 17 years later, it should be possible to build a touch-screen using the same techniques (possibly using layers of transparent conductive and insulating paint for the sensor paths.) Any comments? Some other links: a Microsoft paper (PDF file) describing a touch sensor painted onto a mouse, a basic FAQ on current touchscreen technology, and a slashdot thread that discussed building touchscreens (these links don't address pressure or multi-touch though)."
Re:*sigh* (Score:1)
IT WUZ A JOKE!! (I sincerely hope it was, anyway.)
I understand your point but... (Score:2, Insightful)
Re:I understand your point but... (Score:3, Insightful)
Re:light? (Score:1)
Unfortunately this solution wouldn't cater very well for the multi-touch aspects.
Re:light? (Score:1)
Re:light? (Score:2)
1) No pressure sensitivity
2) When 2 fingers are pressed at once you get 2 X values and 2 Y values (X1, X2, Y1, Y2). So if they both happen at the same time are the fingers at (X1, Y1) and (X2, Y2)? or are they at (X1, Y2) (X2, Y1)? You can't tell. So multiple touches also doesn't work. (If the fingers come in one at a time then you can tell. But the fact that they MIGHT come in simultaniously and that there is now way to tell means you really can't support it)
#2 is a major obsticle to designing a touch system that can actually handle multiple touches. A touchscreen with hundreds of tiny etched "wires" across the inside of two surfaces that "connect" when you touch can get around this and is also widly in use today (Though the "wires" are usually spaced pretty far apart, giving you no more than 10 points per inch resolution or less). But there is no pressure sensitivity. You might have to combine two different technologies to get both.
The best people to build this would be... (Score:1)
> etched "wires" across the inside of two
> surfaces that "connect" when you touch can get
Just as an aside: the most efficient 'layer' to build this would be LCD display manufacturers. The way I see it, they already adress each pixel individually to output data (light); they could do the same to input data (pressure).
your plan... (Score:2, Funny)
2- ??????????
3- profit!!
My business plans (Score:1)
1. Get the slashdot community (which includes myself) to provide plans for a pressure-sensitive, multi-point touchscreen.
2. Build one as a component for my project.
3. Taiwanese/Chinese/American/.... manufacturers notice the plans on slashdot.org
4. Cheap pressure-sensitive multi-point touchscreen become available.
Want more info... (Score:1)
Re:Want more info... (Score:1)
In the billbuxton.com PDF paper, they actually outline a circuit that detects different pressure levels. I was thinking of just adapting that idea to a transparent touchscreen.
Re:Want more info... (Score:1)
You've got a few options... (Score:5, Informative)
I'm betting, though, that you want a real 'touch' screen which registers anything hitting the surface.
Here's what you do: Use a transparent metalization process to put squares of transparant, conducting (but resistive) metal on two opposing pieces of plastic. Take a wire from each square and use a microprocessor with a lot of i/o (switched A/D converters, most likely) to detect which metal plates are being pushed together. The size of the plates determines resolution.
That's the easy, no brainer way.
The cool way (with infinite resolution ) is to use the normal method modified a bit. Normally you have two sheets covered with resistive material, one which has conductors on the vertical sides and one with conductors on horizontal sides. Increase the conductors (say, four shorter conductors on each side, and make them points instead of lines).
Send a signal to one conductor, and listen to all the other conductors for the wave front of the returning signal. Through a ton of signal processing (and sending signals from the others and measuring the response) you'll be able to detect an arbitrary number of points on the screen. You'll need to do a lot more processing to measure surface area (pressure), but you'll get there eventually.
Alternately, you get rid of it entirely and make a video system that can sense the position and movement of your hand and get rid of the 'touchyfeely' altogether. This (IMHO) would be easier and faster to develop.
-Adam
What I was thinking of doing... (Score:1)
> you have two sheets covered with resistive
> material, one which has conductors on the
> vertical sides and one with conductors on
> horizontal sides. Increase the conductors (say,
> four shorter conductors on each side, and make
> them points instead of lines).
Actually, I was looking at using something similar to the circuit in the U.Toronto paper [billbuxton.com]. That circuit seems to require only one layer of sensors that sense touch and pressure by measuring capacitance at the point being touched. I think this method also provides infinite resolution.
I was thinking on the lines of using this idea and painting-on the sensors to the screen with transparent conductive paint. Another layer of transparent insulating paint would cover the track upto the sensor point.
MTC TacTex pressure-sensative pads (Score:3, Interesting)
They have a pressure sensative pad and system you can use, the MTC Express (http://www.tactex.com/prodMTC.htm), however, that is not where you would be interested directly.
Their technology uses fiberoptics in a rubber pad with a small controller. There is a lot of research in integrating their technolgies into other things (a prototype of a complete pressure sensative suit was discussed at one stage).
It fufills your requirements quite well.
256 levels of pressure for each region of the pad independently.
The MTC Express pad had only a DB9 serial connection, and needed a power input as well. However, the OEM material and controllers were a lot more flexible in usage.
Re:MTC TacTex pressure-sensative pads (Score:1)
Existing MultiTouch technology (Score:3, Informative)
http://www.fingerworks.com/
right? They've been mentioned on Slashdot before. Their products can detect multiple fingers at once.
They are selling tablets and keyboard replacements, not touchscreens, but I think I read somewhere (on their website maybe) that they believe it would be possible some day to use this tech in a touchscreen.
The cool thing is it sees your whole hand via infrared, so it can tell which finger you're using. For the first time, you can "right click" on a touch surface, or use other finger combinations/gestures for various operations (drag, pan/scroll, rotate, etc.)
Re:Existing MultiTouch technology (Score:1)
Do you need to be bare handed? (Score:2)
If not, you might think about using a standard touch screen system, then building (or buying, if they exist - probably don't) pressure sensitive "gloves". For the sensors (at the finger tips), buy thin ribbon plastic tubing (multiple tubes joined in a ribbon - used in many continuous ink kits for ink-jet printers, so you should be able to buy it somewhere by itself), spread one end and seal the ends of each tube, apply gentle heat and blow "bubbles" at the end of each tube (this may be difficult, but not impossible). Then, attach these bubbles to the fingertips of the gloves, and use a T-connector on the other end of the cable to hook the tubing to a very low pressure air supply and the other side of the T-connector to a air-pressure transducer. Hook the transducers up to a PIC or Stamp (or other ADC system) to measure the pressure change (the positive pressure keeps the bubbles inflated at all times, and reinflates them after being depressed - a closed system might work too, with no active pressurisation - you might have to experiment here).
Other cool things to do with the gloves:
1. Touch gestures (like a chorded keyboard)
2. Use water instead of air, then warm or cool the water with a peltier to provide feedback.
3. Pulse the pressure for other feedback needs.
Hope this helps...
Re:Do you need to be bare handed? (Score:1)
Applications? (Score:1)
Anyone else have ideas what this could be used for?