Robust user interface requirement

No ideas except a suggestion - is there anything used in gaming / pinball / arcade games that may suit? They'd take a hammering.

Can you put buttons around the edges of the screen instead? You get quick use, lots of flexibility, and real buttons.

--
Tim Wescott 
Control system and signal processing consulting 
www.wescottdesign.com

Hi Bruce,

When you say "poked" is that with a human finger?

Does a screen need to display information in order for a selection to be made. How big an area do you need and does it have to be very rigidly mounted? How changeable is the selection infoirmation?

So far the screen on my Acer Iconia has withstood some heavy pokes from some people who have accidentally jabbed at it when identifying something of interest. However, I am not certain it could withstand someone who is very heavy handed. I would have thought most musicians were dexterous enough to be able to use such a device though.

--
******************************************************************** 
Paul E. Bennett IEng MIET..... 
Forth based HIDECS Consultancy............. 
Mob: +44 (0)7811-639972 
Tel: +44 (0)1235-510979 
Going Forth Safely ..... EBA. www.electric-boat-association.org.uk.. 
********************************************************************

But, that "poke" wouldn't damage a CRT or LCD (with a lexan face)? I.e., you're not worrying about drummer taking a swipe at it with a stick!

How fast is fast? And, is it "fast" because it needs to be "of short duration"? Or, because the operator is taking a careless *jab* at it? Presumably, its a *set* of controls that the user needs to be able to freely and independantly access? Not just "move to the next preprogrammed preset"

But, the time to press a pushbutton isn;t necessarily short -- depends on the mechanics of the button and how reliably it stays (?) pushed (are these momentary or latching/toggle?)

You want a relegendable button, effectively?

Does the legend have to be graphic? Multichrome? etc. How precisely can you expect users to *find* the button? I.e., does the size need to be variable as well? (of course, you have very little flexibility with your existing mechanical buttons in this regard. But, are all your mechanical buttons the same size? Nothing the equivalent of an EMERGENCY STOP??)

How many buttons in what sort of space (area)? Any size/weight/cost constraints (naw, those things never come into play! :>)

There are lots of choices for touch screen technologies. [I'll restrict my comments to these, initially. There are also *other* approaches you might want to investigate]

Most technolgies assume that you have a firm surface against which the "actuator" (finger, tylus) can operate. I.e., a *typical* LCD monitor has a flimsy plasic "film" so pressing on it will actually damage the display! Most originate in the CRT days so you had a significant bit of glass that the user could interact with mechanically without damaging the display.

If the points on the display surface are relatively few, you an use a bezel of photoemitter/detector pairs. Beams of (Ir) light IN FRONT OF the display surface. Watch to see which *2* (or more -- for folks with fat fingers :> ) beams are interrupted -- one X ,one Y -- and you know where the finger has touched the screen.

These are relatively easy to calibrate -- the emitters/detectors have fixed locations so *they* require no calibration (though they must be aligned properly with their mates). You do, however, need a way to ensure the image *behind* the array "fits" its dimensions (cuz your software expects pixel (x,y) to be "behind" a particular set of emitter/detector pairs). For a CRT, this means adjusting height and width in the monitor (or, comparable scaling in the video generator). For an LCD, it's not an issue! Just ensure the registration of the touch panel wrt the display itself (left/right, up/down).

The downside is this approach costs more emitter/detector pairs to get finer "precision" in "finger reporting". Conversely, if you don;t need to "see" fingers in some portion of the display, you can omit the emitter/detectors that would otherwise be needed to cover that part of the display! "Speak now or forever hold your peace"

This can be power hungry, relative to other approaches. One way to conserve power is to multiplex the drives. But, that increases the amount of time it takes to reliably *see* an finger. (if you have 50 emitter detector pairs on each axis, muxing can save A LOT of power!) So, you tend not to get *big* savings because you don;t want to increase the "scan time" for the entire array.

[You can, however, easily do "X detect" followed by "Y detect" and cut power in half for very little sacrifice in response time *or* hardware cost.]

Another optical variation uses a fixed, rotating light source that sweeps the screen. Less power in the optics -- but now you have mechanism to attend to. And, slower responses.

In the first approach, failure of *a* detector or emitter causes the loss of a row (or column) sense. Depending on where your buttons are (and, if they can be relocated dynamically), you may lose some number of buttons related to that dead row/column. With the rotating beacon approach ("Cyclops" was one commercialized name), failure of the beacon (optics *or* mechanics) meant the entire detector was shot.

[I offer this as I suspect most performers aren't keen on repairing kit during performances -- though they may have the ability to do so!]

You can also optically detect the deflection of a clear membrane suspended *above* the display surface. Hunt for the "bright spots" on each axis to indicate the points of maximum stress, etc.

You can also require the finger to be "active". The classic case was the lightpen -- a photodetector tethered to the display in a pen body. Essentially, when it "saw" the scanning electron beam from the CRT, a snapshot of the "address" being accessed by the crt controller was made. This could be interpreted to determine which row/colum *pixel* was being seen at the time.

Of course, reports happened at the frame/field rate of the display; you couldn't be guaranteed to "see" anything until all pixels had had a chance to "shine".

Similarly, you can have a light source *in* the finger (ET phone home) that sensors in the display's *frame* detect.

The same is true of active digitizing pens, etc.

I imagine you *don't* want the user to have something in his hand to ineract -- even if it was *permanently* in his hand for the duration of the gig!

Touchpads in PDAs used a membrane overlay. Two conductive transparent sheets of plastic held apart by invisible separators. Pressure on the outermost deflected it so that it would come into contact with the inner (closer to display) surface. The "adjacent" surfaces of each membrane were coated with a resistive material. A potenial would be impressed across one membrane. The voltage drop at any point X% from the edge of that membrane would be X% of the impressed potential. (imagine an infinite number of identical resistors in series).

The *other* membrane would be used to *sense* the potential at the point of contact -- the entire membrane would feed an "A/DC" that was configured ratiometricly wrt the excitation voltage on the other membrane. I.e., 000000 meant the contact point was exactly at the "lowest potential end" of the membrane while 1111111 meant it was at the highest potential end of the membrane.

[pictures would be *so* much easier to explain!]

Repeat the process exciting the membrane along the other axis. Combine these two A/DC readings and you have a spot in 2-space. Speed of A/DC determines how quickly you can resolve location on an axis. Number of bits in A/DC determines how many positions you can resolve ALONG that axis.

These were popular because they were inexpensive to produce. Esp in those small sizes (imagine, for example, trying to sense position on a small display with *optics*!)

Problem is, they interfere with visibility -- decreasing light output (or "throughput" for transflexive displays) and making things a bit fuzzier. And, as they represented a genuine surface *above* the display, they were susceptible to damage -- the (separated!) membranes were typically softer than the surfaces that supported them so they would get gouged, etc.

In your case, as the membrane is expected to deflect, too abrupt a motion can cause it to "bounce back" -- before you get around to noticing it (you would need to do your own controller to ensure you poll fast enough)

The same sort of approach can be done capacitively. There are different approaches to capacitive detectors. E.g., each of the previously mentioned techniques will successfully detect a drumstick used to actuate a virtual button. Capacitive detectors tend to rely on the human body *in* the circuit. Gloved hands can cause problems (as would a drumstick, etc).

I'm particularly fond of SAW (surface acoustic wave) technology. Essentially, a "sound" (inaudible) is coupled to the glass (CRT invariably). Your finger (or other material) contacting the glass changes the characteristics of the "sound" when it reaches the detectors ("microphones"). This lets the controller determine the interference is located. It's biggest advantage is that it also lets you detect (relative) *pressure*, not just location.

But, anything that changes the characteristics of the "acoustic conductor" affects its accuracy. E.g., get it wet and it behaves differently than when dry! (It's also not immediately obvious to users that a given pressure from their *thumb* may be interpreted entirely different than the same pressure from their index finger! Or, *your* index finger!)

Again, in your application, this is a slower technology. The frequency of the "sound" effectively sets a polling rate (can't see the result until you've got a signal to recognize!) as does propagation delay through the glass (1-2 ms just for the signal to get across the surface!)

(sigh) I've probably forgotten a technology or three...

*If* you can afford the cost (materials & labor) *and* have a low enough "resolution", I suspect the emitter/detector array will give you the quickest RELIABLE scan. (you don't want a performer to have to repeat the action because it wasn't recognized the first time!) It's not as elegant as many of the newer approaches but you asked for robust, not elegant!

If these buttons were just presets or effect in/out, you might also consider allowing them to relocate themselves (or, be relocated by the performer) in the event a detector fails, has BBQ sace spilled on it, etc. The Show Must Go On.

Or, even a semicustom design: imagine strips of flexible plastic each fed by an emitter on one end and sensed by a detector on the other end. When the strip is deflected *anywhere* along its legth/width, the light output conducted through that strip drops off...

(sigh) Lots of word. Hopefully some will help.

You might also want to consider other input modalities, depending on the choices/controls you are trying to provide...

--------------------------------------------------^^^^^^^^^^^^^^

I think the issue is that the operator wouldn't have *time*/luxury to do this in a leisurely fashion. The equipment may serve a real, needed purpose -- but, it's a distraction from PLAYING MUSIC.

Consider most musical instruments require both hands to play (harmonica requiring none?) and usually some amount of concentration and visual "attention". Looking up from a keyboard (organ) to see which button you want to press (i.e., identify its location in space) AND then pressing it -- without skipping a beat in your performance probably means you *throw* your hand at it instead of finely positioning your finer as you might on a computer keyboard.

Sort of like the SCAN buttons on car radios... just slap it and let*it* find the next station -- instead of having to focus your attention on that task.

Soft keys! That's what they're called. Something like this is what I have in mind:

It's used on many many pieces of test equipment, and it works great. You'll need to be diligent about having a reasonable menu structure, but you needed to do that anyway.

--

Tim Wescott 
Wescott Design Services 
http://www.wescottdesign.com

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yep modern capacitive touch works through glass, I've read that some work t hrough at least 6mm

another way I remember from way back, to to have a stiff plate such as glas s on three force sensors and sorta "triangulate" the point of touch

-Lasse

For the OP, I think the problem will be how quickly it can be sensed and how stable the "finger" can be in that time interval.

Someone made a (CRT) "monitor base" many years ago that did exactly this. Set your monitor *on* it, calibrate and you have a touch monitor.

I suspect this would be bad for the OP solely based on the mechanics involved -- monitor jiggling as it is "struck", etc.

I was referring to a touch-screen slate which, in touch screen mode, has proved reasonably robust. The Acer Iconia might not suit Bruce's price/performeance point though. I am sure other touch screens might be similarly robust and provide reasonable sized areas for menu selection by touch.

--
******************************************************************** 
Paul E. Bennett IEng MIET..... 
Forth based HIDECS Consultancy............. 
Mob: +44 (0)7811-639972 
Tel: +44 (0)1235-510979 
Going Forth Safely ..... EBA. www.electric-boat-association.org.uk.. 
********************************************************************

Understood. My point was that the "actuation time" (how long the "finger" is in a "sense-able" position might be too brief for many technologies to "see" reliably.

If his users are so "hurried" that they can't take the time to "deliberately" actuate the screen, they probably would be even more annoyed to notice that their attempt had not been registered (perhaps not noticing until after they had SUCCESSFULLY invoked some other function) and that they would have to adjust their actions on the fly to re-touch the original control.

IMO, that was the "real problem" Bruce is facing (moreso than durability).

Looking at Bruce's original post, he has accomplished the task with normal pushbuttons and keypads before. I have noticed that my touch screen seems to be at least as quick as that method and may just give the versatility. I was just not sure the price/performance point would be right for him. The qustion would be regarding re-purposing a touch screen device to act within reasonable time for this function and give the fleibility he was after.

--
******************************************************************** 
Paul E. Bennett IEng MIET..... 
Forth based HIDECS Consultancy............. 
Mob: +44 (0)7811-639972 
Tel: +44 (0)1235-510979 
Going Forth Safely ..... EBA. www.electric-boat-association.org.uk.. 
********************************************************************

Yes, but they are mechanical devices. Push it hard/fast/slow/soft and those metal contacts still come together -- regardless of how briefly. (depends on how you scan them).

I assumed he was looking to OEM something -- using components and not repurposing an existing device. Hence my litany on different touchPANEL technologies.

I've had very bad experience with touch pad response times.

PDA's (resistive) and older phones seem to be "adequate" when used with a stylus (as long as your "jab" doesn't "ding" the touch overlay). But, require more "deliberate" effort with a fingertip. Even seemingly hard "taps" get ignored if too brief.

SWMBO has a habit of "stabbing" the "YES" button on the signature pads at checkouts ("Is this amount correct?") and having to do so repeatedly (not that she is missing the "box" but, rather, her actions are too "staccatic"). I have dismissed this as related to the amount of abuse these devices must typically encounter!

And, some assistive technology devices (press here to say "Please bring me some water" and here to say "I need to go to the bathroom") that are *very* difficult to coerce into "seeing" a button press. I've assumed this was a consequence of needing the display to be extraordinarily robust given motor skill limitations of its users.

I have (large LCD) panels from three different manufacturers with SAW technology that also seem to want deliberate actions.

This tablet PC uses an active digitizer yet the pen often fails to register a click. I've grown wary of letting others use it as they invariably start STABBING the display thinking that will make the click happen more reliably (in fact, all it will probably do is crack some ferrites!)

OTOH, I've used some touchPADS (i.e., the small things in keyboards) that would register a click if your hand hovered above it! :<

As I can't peer inside at their implementations, I can't tell whether these are inherent limitations of the technology, "filters" added to reduce false positives or otherwise driven by the applications.

I figured the photointerrupter approach to be the least risk up front: beam gets broken, you see the finger's location instantly!

Bruce will have to sort out what his practical concerns are.

2013-11-17 13:04, Bruce Varley skrev:

You can have capacitive touch buttons. Work like a touch screen, but no mechanics, just electronics and a sensor which is just a certain layout on a PCB.

BR Ulf Samuelsson

I did an interface for data collection on fishing boats that used configurable LCD prompts and capacitive touch sensors behind a 1/8" polycarbonate panel. It was waterproof and, with a bit of tuning, even able to register touches from users wearing rubber gloves. The waterproof part might be useful if the performances will occur in bars where bottles may be thrown by dissatisfied customers!

Mark Borgerson

Not sure if you can run Python, but the Kivy project has a music synthesizer as a sample application in the gallery section, might give you some ideas of what is possible these days ...

kivy.org

HTH, Cheers, Rob Sciuk