May 23rd, 2004, 10:13 PM
Using touchscreens and their linux compatibility
I've recently been thinking about a little project that I'd like to do. At the moment I share a car with my mum, but if I get a car of my own, I'd like to make some slight modifications ("what does this have to do with computers?" you ask!) Anyhow, I was thinking that I could create a cheap computer (thus it would run linux) with a touchscreen that I would mount in the front of the car (and an external hard drive that I could take into the house to load songs, etc. on to it).
My question is, does anyone know any linux compatible touch screens, and how they work (how they are connected to your computer). Also, another problem I've been wondering about is the fact that I don't wanna manually shut down the computer every time I stop the car...any suggestions?
I'll keep on searching the web, but if anyone has had experience with something similar I'd be grateful if you could reply. Thanks.
 could someone also explain what the difference between resistive, capacitive and SAW touchscreens? (I understand what resistance and capacitance are...) [/edit]
May 24th, 2004, 10:23 PM
Resistive touch screens are by far the cheapest (but still quite expensive) but offer the lowest quality and work by having a glass screen coated with ITO (indium tin oxide) which is a see through semiconductor, over this goes a clear fairly robust peice of plastic. When you press on the plastic is makes a contact with the ITO compound (which remember is a semiconductor ) and this completes a curcut. Where you press is calculated on a X,Y axis and this info is fed into your computer, and it acts accordingly
A capacitivte touch screen, is slightly more expensive and works by producing a electric field which spans the whole of the screen, when you touch the screen, you create a disturbance in the electrical field and this again is registered on a X,Y axis, to mark the postion you touched and the info is fed to your computer.
* it also requires skin contact to operate.
SAW or Surface Accoustic Wave are the most expensive but by far the most accurate screens. A SAW screen has a set of reflector stripes and a transmitting and receiving piezoelectric transducer(PT). a controller send a 5mhz burst/wave to the PT, which then convert this signal in to accoustic waves, the reflector strips then divert this burst accros the face of the screen.
When a stylus (which is usually used with this type of screen as opposed to a finger, due to the accuracy that can be acheived with this screen) touches the screen, a part of this wave is absorbed, the change in this wave is the registerd by the receiving PT and translated into a X,Y axis the accuracy comes from adding a further A,Z axis in to it which measures how much of the burst was absorbed, therefore registering how far away from the receiver the screen was touched.
As for a linux screen i dont really think it will make a difference what os you use much the same as a monitor will work now with any os, im not sure about this though as I have only had dealing with windows platforms and touch screen monitors.
The only reason that it wouldnt work would be any drivers that are required. As without the drivers the monitor itself will still work but you will have to you a mouse to interact with it, much the same as when you boot up in windows in safe mode, if you have a touch screen it will still display things but you will need a mouse!
Hope it helps a bit!
edit\\ you can get "kits" that turn exisiting monitor into a touch screen monitor and as it is an ordinary monitor it does not matter what o/s you use. this may be a cheaper alternitive for you if you want a touch screen in your car?
May 25th, 2004, 01:57 AM
Thanks for the reply. I think I'm probably as well just buying a touchscreen rather than getting a kit because of the fact that I don't have any monitors that are small enough for this purpose. I understand that the only limiting factor with getting a touchscreen to work in linux would be the drivers, was just wondering if anyone knew of any screens that had linux drivers for them.
Anyhow, thanks again. Your post was fascinating and you gave me more than enough information. Now all I need is a car to do it with :P
May 25th, 2004, 02:13 PM
LOL, no probs mate, glad i could help you out!