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Cheap, Small LED or LCD Touch Sensitive Screens? 39

emf2268 asks: "I'm looking to either purchase or build (I'll do the circuitry myself if I have to) several dozen, small screens for an arcade game that uses a touch interface. Each screen, which should be around 6-10 inches, needn't be extremely advanced in the display department, since 16 colors will do just fine. An LED or LCD would do the job. But each screen also needs to be touch sensitive...it only needs to know if it's been touched, not where it was touched. How, can I build this as cheaply as possible?"
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Cheap, Small LED or LCD Touch Sensitive Screens?

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  • glasspane (Score:3, Informative)

    by yincrash ( 854885 ) on Monday April 10, 2006 @06:33PM (#15102306)
    the cheapest way to do this is to probably have a small (plexi)glass pane over the cheapest display you can find and have the glass pane be resting on a bump switch(sensor) that has enough tension to hold the glass up but will register when it is touched.
    • I concur with this one. Make them as bulletproof as you can get them, if the construction of DDR is any guide to go buy, steel, rivets/welding, and 3/8ths thick (or thicker) plexi is the way to go.

      Design it as though an elephant will stomp on it, and then maybe it'll last long enough for you to enjoy it
    • Re:glasspane (Score:2, Informative)

      by yincrash ( 854885 )
      to extend upon this, you want to make sure that when the pane is pushed down, it doesn't actually touch the screen. i'm sure there is a way to mount it so when fully depressed it is barely above the screen.
  • What I use (Score:2, Informative)

    What I have done in the past is to buy a bunch of old Windows CE.NET devices off of Ebay and use their touchscreens. For some (like the Aquapad) you can even get Linux drivers - search for Midori Linux and Aquapad.

    Its certainly cheaper than trying to source new screens.
  • I would say get LCD screens that you can mount onto buttons yourself. Since you only have to recognize touch (and not location), it would probably be much cheaper than purchasing touch LCD screens, since most of them are designed to tell you where they were touched.

    I would say mount 5 buttons on the back (center and each corner) and then wait to see if the screens were "pressed" by checking all buttons. If any register a touch - then the screen was "pressed".

    RonB
    • i'm going to have to say it's proably a bad idea to be putting force on the actual lcd screen itself if you're going with lcd. after a couple of months of finger pressure on the lcd, you're probably going to start showing up marks or dead pixels. this method puts too much stress on the lcd.
  • PPR? (Score:2, Funny)

    by Anonymous Coward
    Punch Punch Revolution?
  • Single button screen (Score:3, Informative)

    by Ydna ( 32354 ) * <andrew.sweger@net> on Monday April 10, 2006 @06:37PM (#15102340) Homepage
    If all you need is to detect a press anywhere on the screen without regard for where it was touched, just get small LCD display guts and float them on spring loaded contact switches and wire that switch up to some input.
    • Yes, I like this better than the separate piece of plexi over the screen, and it's probably the simplest possible answer. You might have to use 4 microswitches wired in parallel behind the corners of the display to guarantee that one of them gets pressed no matter where the display is pressed.
  • by AndroidCat ( 229562 ) on Monday April 10, 2006 @06:42PM (#15102370) Homepage
    Unless your game is Sim Paint-Drying, I think you'd be better to have an actual switch to press rather than have the player press the screen. Excited humans don't know their own strength, and I've seen industrial coin-op joystick that were yanked out by the roots.
  • Real cheap (Score:3, Interesting)

    by Peter Simpson ( 112887 ) on Monday April 10, 2006 @06:51PM (#15102428)
    If I were trying to do this on the real cheap, I'd use conductive bags. Cut a square of the material, place it backwards (inside out) over a plexi backer, with the LEDs behind it. A non-conductive) bezel over the front to keep all in place. Connect the conductive inner layer of the bag material to a high impedance circuit with a spring contact and sense the "body antenna effect" (as on the old microwave ovens),

    It's much cheaper than metallized glass. But maybe you want to go that way.

  • Old fashioned way (Score:2, Interesting)

    by cyber_spaz ( 302607 )
    Back in the day, we used to see articles for homebrew touch screens that were basically picture frames with a few infrared LEDs on one side, and some phototransistors on the other with a bit of circuitry. Your finger would break a beam and get detected.

    For a tiny production run, this might be an acceptable method. (For a *real* product, you'll want something better.)

    Another thought: If you can get a conductive transparent plastic sheet, then you could make a sandwich where one sheet is against the scree
  • As the adage goes (Score:4, Insightful)

    by Dachannien ( 617929 ) on Monday April 10, 2006 @06:54PM (#15102446)
    Cheap, small, and good. Pick any two.

  • by saccade.com ( 771661 ) on Monday April 10, 2006 @07:24PM (#15102605) Homepage Journal
    It turns out you can use LED arrays as both displays and sensors. People have successfully used them for touch sensor controllers. See this blog [dimension-x.net] for some experiments. The original concept came out of the NYU media lab.

    • Note that these require a lot of circuitry to run, and all prototypes currently only work in dark environments (the LEDs sense their own light, sure, but also room lights, sunlight, etc).

      Currently a neat hack with perhaps some niche uses, but not a good general solution.

      -Adam
  • by Facegarden ( 967477 ) on Monday April 10, 2006 @07:30PM (#15102626)
    Resistive touch panels (not including the screen) are incredibly simple and cheap... They can register position, but if you don't care, you can still use them to see if they've been pressed. Get some palm-pilot touch panels, peel off the overlay on the back for the graffiti section, and you have a nice ~4 inch touch sensor. Buy custom sizes from a place like 3m or digikey, or get old palm pilot touch panels (no screen, just the touch part) for $4 each from http://www.halted.com/ [halted.com] Look up how they work... they basically act as a voltage divider when pressed... a simple comparator circuit is all that you need to register a press, and it's much more elegant than resting the screen on a push switch... -Taylor
    • Last time I called them (about a year ago), 3M sold a sample quantity of conductive/resistive transparent film for $900. It was a decent deal if you wanted touch sensitive displays in bulk, but for one-off projects of a custom size it seems like you're out of luck.

      Digikey has all sorts of driver ICs, but I don't see anything to actually make the touch sensitive surface there. Am I missing something?
      • 3m sells pre-made glass or plastic panels with the leads and everything all ready to throw on a screen or whatever... though I'm not sure through who. I thought digikey sold them... maybe it's Arrow... I know I've seen them recently... Maybe they weren't 3M... Maybe search for "resistive touch panel supplier" or something and see what you get... -Taylor
  • just get an optimus keyboard, they have lots of OLEDs and it's touch sensitive since it's a keyboard. http://www.artlebedev.com/portfolio/optimus/ [artlebedev.com] oh, you may have to wait a little while for the release of this product, the prototype will be ready any day now...can't wait to use it to play DN Forever.
  • LCD touch (Score:5, Informative)

    by nan0 ( 620897 ) on Monday April 10, 2006 @08:37PM (#15102928)
    earthlcd has been a savior on many a project

    http://store.earthlcd.com/ [earthlcd.com]

    if you really just need on/off - do the spring loaded, or piezo, or even IR (www.acroname.com - sharp ir sensors)

    if anyone has any other leads on cheap overstock LCDs... post away!!!
  • by dr_leviathan ( 653441 ) on Monday April 10, 2006 @08:43PM (#15102960)
    (1) capacitive switches -- inexpensive, digital (on/off)
    This reverses the idea of protecting a high-impedance circuit from stray capacitance introduced by a limb or finger -- turn your accidental 'people detector' into just that:

    http://www.discovercircuits.com/C/capacitance-sw.h tm [discovercircuits.com]

    (2) frustrated internal reflection -- not necessarily cheap (needs a camera), or easy (needs video analysis) but can handle multi-touch and large screens
    The idea is to shine light in from the side of a class or plastic screen, and have a camera look at the backscatter introduced by finger contact, which scatters the sidways light rather than allow it to reflect at the bounary. The camera turns the touch events into a video stream which is then analyzed to compute touch events.

    http://mrl.nyu.edu/~jhan/ftirsense/index.html [nyu.edu]

    (3) strain gages -- not necessarily cheap ($5 - $8 for each strain gage) but can provide a very sensitive analog signal with wide dynamic range.
    Put some strain gages on several centimeters of half-inch square steel tube and you can easily measure touch events, as well as strong pushes.

    http://www.omega.com/literature/transactions/volum e3/strain.html [omega.com]

    Here is a simple, inexpensive (if you make it yourself) amplifier for strain gages that I've tried, and can vouch that it works well:

    http://www.staramp.com/ [staramp.com]
  • LCD screens for in-car DVD systems are available in the 6- to 10-inch range, in 4:3 and 16:9 aspect ratios, and are getting cheaper all the time.

    Although they tend to have composite or S-video inputs (you're not really after high resolution, are you?) there are some now getting VGA inputs and touch screens [jaycar.com.au] for in-car computer applications. You can just register that the screen has been touched and ignore the actual location.

  • by euxneks ( 516538 ) on Monday April 10, 2006 @10:10PM (#15103342)
    I found this neato LED interface [nyu.edu] the other day from hackaday [hackaday.com]
    Some more links to projects like this can be found on the story [hackaday.com] on hackaday.
  • by LarsBB ( 516200 )
    LEDs are photodiodes too! http://mrl.nyu.edu/~jhan/ledtouch/index.html [nyu.edu]
  • Why several dozen? (Score:3, Insightful)

    by cgenman ( 325138 ) on Monday April 10, 2006 @11:58PM (#15103768) Homepage
    Why several dozen for an arcade game? Will this be used as a prototype menu interface, or are kids going to be thumping on this thing with rubber mallets at the museum of science?

  • i would just go with a glass panel to take the beating and fingering and a couple of infrared LED emmitter/detectors.. only reasoni see for using the actual touchscreen was if position was important, and it also sounds liek you are trying to make a game? or wh the just detect if touhced or not? touchscreens are less touchable

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