Cheap, Small LED or LCD Touch Sensitive Screens?

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?"

Comments

glasspane

[yincrash]

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.

Re:glasspane

[yincrash]

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

[110010001000]

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.

Single button screen

[Ydna]

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.

Touch panels are cheap and easy...

[Facegarden]

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/ 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

LCD touch

[nan0]

earthlcd has been a savior on many a project

http://store.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!!!

three interesting ways to do it

[dr_leviathan]

(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

(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

(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

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/

You should look at this

[LarsBB]

LEDs are photodiodes too! http://mrl.nyu.edu/~jhan/ledtouch/index.html