Need giant touch-surface... Ideas?

I say "touch-surface" rather than touchscreen because I don't necessarily need an actual screen or display, just a surface that can sense precisely where it's being touched. I need a BIG surface (about 4" wide and about 40" long) with preferably millimeter or sub-millimeter precision, and multitouch capability. The UI will be a physical graphic painted or etched onto the surface (hence I don't need a lit display), and it'd be nice if there was the ability for the whole surface to be transparent but I won't get ahead of myself if that ends up being difficult. The main thing right now is: how do I get a giant, precise, multitouch surface that can interface with Arduino (or a Teensy or Pi if I need more power) without spending a fortune???

Capacitive sensing like what's done on phone screens might get you finger close, it'd be a big project.

GoForSmoke:
Capacitive sensing like what's done on phone screens

This occurred to me, but not sure how exactly to do that. The only experience I have with capacitive touch is using up to four MPR121 breakout boards, which only gets me 48 electrodes. How do smartphone screens do it in such a high-resolution matrix?

You'd have to read up on how the phone screen does it, IIRC some only detect 5 spots and calculate from capacitive differences.

I've used beam-interrupt touch screens in the 80's. The lights and detectors were in a frame that went on the front of the CRT and could sense a finger as 2x2 squares. For 4" x 40".... major building, wiring, coding, likely a lot of chips.

That 1 or 2 mm part makes the job hard.

How do smartphone screens do it in such a high-resolution matrix?

The phone is sensing big fat fingers, and usually only cares about relative motion, for panning, zooming, etc.

Try selecting text in a text message, to edit it, and see just how "high resolution" the sensing is. Usually can't even get the correct line, let alone the correct start or end character.

Squirt_5432:
I say "touch-surface" rather than touchscreen because I don't necessarily need an actual screen or display, just a surface that can sense precisely where it's being touched. I need a BIG surface (about 4" wide and about 40" long) with preferably millimeter or sub-millimeter precision, and multitouch capability. The UI will be a physical graphic painted or etched onto the surface (hence I don't need a lit display), and it'd be nice if there was the ability for the whole surface to be transparent but I won't get ahead of myself if that ends up being difficult. The main thing right now is: how do I get a giant, precise, multitouch surface that can interface with Arduino (or a Teensy or Pi if I need more power) without spending a fortune???

Would something like a digitizer tablet work? I used to sell and install these tablets which were used to digitize maps into CAD systems. Accuracy: ± 0.010” (0.254mm) or ± 0.005” (0.127mm). The tablet is not touch sensitive; you have to press a button to output a point or you can set it to output a stream of coordinates as you move the cursor across the face of the tablet. The output is ASCII through a COM port so the interface to an Arduino should be no problem.

Google the right thing! eg large area touch screen

Mark

Also "electronic whiteboard" may also get you closer to what you want. Multi-touch might be impossible with that technology however.

4' x 40' that's 1230 x 12300 mm.

mm-level resolution means you have 15,129,000 points total. If you use a grid of break beam sensors (good luck getting that to work at 12.3 meters distance) you need at the very least 13,530 sensors. That are ridiculous numbers, and won't work for that simple reason.

Maybe you should have a word with these guys. They claim to have a 102" (2m59) diameter touch screen available. About 8 of those should get your wall done. A quick search on their web site didn't turn up any info on screens larger than 84", though 102" is mentioned on their front page. The displays may even be multi-touch.

4 x 40 inches

GoForSmoke:
4 x 40 inches

Misread that.
Mostly as OP was talking about "giant".
Makes it easier. A few bezel-less phones (or tablets, if they exist) placed side to side should do the job to create such a screen.

GoForSmoke:
some only detect 5 spots and calculate from capacitive differences.

Thought of doing something like this, is multitouch possible with that? If so then it might be perfect but I'm not sure how that would happen

PaulS:
Try selecting text in a text message, to edit it, and see just how "high resolution" the sensing is. Usually can't even get the correct line, let alone the correct start or end character.

This was true a few years ago, but my Galaxy S9+ has no problem selecting between desired characters (small ones at that) first try. I just need a version that's about 10 times bigger lol

oldvetteguy:
Would something like a digitizer tablet work?

Kind of, if I can get one big enough and supporting multitouch (and preferably one that doesn't cost an arm and a leg)

MorganS:
"electronic whiteboard" may also get you closer to what you want. Multi-touch might be impossible with that technology however.

An art class I took had one of these that I got to use, that's the right direction but I really need multitouch, and also the response time on it was a bit slow for my purposes. I like your thinking though, I remember being impressed with it when I first experienced it.

wvmarle:
A few bezel-less phones (or tablets, if they exist) placed side to side should do the job to create such a screen.

Technically that might work, but I'd like it to be a smooth continuous surface and also doing that would mean many thousands of dollars spent on additional features in the phones which I don't need. Theoretically that's in the right direction though.

There are also bare displays out there, with touch option. I don't know if they're multitouch or not, and the movement between screens is going to be an issue. You probably need a more powerful controller than an Arduino to control them - think Raspberry Pi or something like that.

It's quite unlikely that you find an existing screen of your size and dimensions. Especially the very long shape is highly unusual.

wvmarle:
It’s quite unlikely that you find an existing screen of your size and dimensions. Especially the very long shape is highly unusual.

Oh I’m aware - I’m pretty sure I’ll have to make this myself, just not sure to what degree. This is just the main part of a bigger project, so I’ll want to custom-build it into the rest of the thing anyway. I’m willing to learn how to do it, but this particular thing has been difficult to Google without just being bombarded with existing products that don’t fit my needs.

Also want to reiterate that I don’t necessarily need an actual screen, just a touch-sensitive surface on which I can paint or etch permanent graphics.

The whiteboards I used to use were NOT "touch sensitive", they had (possibly infra-red) scanners top/bottom and left/right. And they were multi-touch, because you could zoom in/out using two fingers.

Perhaps a call to some white-board manufacturers would be in order.

PS. I'll see if I can find out who makes the ones I've used tomorrow

SMART Technologies

Take note of times 2:50 and 4:46