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Registered Member #902
Joined: Sun Jul 15 2007, 08:17PM
Location: North Texas
Posts: 1040
in a multitouch display (like the iPhone) is it the processor integration or the screen itself (somehow different) that allows the use of multiple fingertips?
I plan to build some long touch screens and thought that the capacitative sensing might be a good idea, but need to know if it has to be built a special way for multitouch to work...
Registered Member #27
Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058
It uses a grid of vertical and horizontal conductors to detect the changing capacitance in different places on the screen. It is nothing special, the controller is an ARM based microcontroller. There are at least 6 ARM processors in the iPhone.
Registered Member #1497
Joined: Thu May 22 2008, 05:24AM
Location: Toronto, Ontario, Canada
Posts: 801
I think that multitouch is processor based, all a touchscreen is is a grid of perpendicularly aligned wires that touch each other, in essence a large keypad. You can sense that multiple points are 'on', but being able to track multiple points and use the position information to control objects took much longer to develop.
Another example of multitouch that has been around much longer than the iPhone is the lemur ( )
Registered Member #902
Joined: Sun Jul 15 2007, 08:17PM
Location: North Texas
Posts: 1040
I know it is capacitive sensing (my mistake if I did not make that clear), but I do not know if it needed modifications to work for multitouch, as I plan to build a multitouch display for a project of mine...
Registered Member #56
Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445
It is a hardware change. The normal way of having a grid of sensors (capacitive, resistive, light, etc) with a controller for each row does not work for >2 points, because of you have 2 points on the same row/column you can't determine where the points are.
Registered Member #902
Joined: Sun Jul 15 2007, 08:17PM
Location: North Texas
Posts: 1040
... wrote ...
It is a hardware change. The normal way of having a grid of sensors (capacitive, resistive, light, etc) with a controller for each row does not work for >2 points, because of you have 2 points on the same row/column you can't determine where the points are.
Registered Member #56
Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445
By far the easiest way is to just shine a camera at the display. The normal technique is to use a plexiglass display, with IR edge lighting, and a projector shining on it from underneath (the inside surface probably needs to be fogged), and a camera with a visible light blocking filter to see the IR light. Where you touch the glass it screws up the internal reflections of the IR light, and created a bright dot, easily seen by the camera.
the iphone uses some kind of capacitive sensor array that is underneath the screen, where each sensor is independently addressable and gives a value of how close your finger is to it. I believe they use some kind of triangulation between the sensors, but it might just be that there is a big grid of them. You might be able to find the patent for it (I believe it is owned by the screen manufacturer).
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multitouch displays: processors or sensors?
