Capacitive touch screens

[Jane]

Can anyone suggest any tutorial/ study text where I can learn how capacitive touch screens work?
Is there any method how to test a capacitive touch screen? E.g. there is a capacitive touch screen in a cell phone and it can start to behave in a wrong way; for example  I click on one letter and it writes a different letter or several letters in one click.
So an error can be caused by a touch screen itself or not. So my idea would be to dismantle the cell phone and measure the touch screen somehow. Possible way or not a good idea?
Thank you for feedbacks

[miguelvp]

Get a free app that tests the touch screen like "multi touch benchmark" for Android, if IPhone I bet they have apps like that as well.

[sacherjj]

You are going to learn more by reading many of the articles on capacitive touch screen operation on the net.  Touch screens have chips that read capacitance between horizontal and vertical bands.  These portions of the circuit or pretty sensitive.  Also, the chips are programmed with offsets, based on surrounding structures and metals.  Once you build a touch screen into a device, you sometimes need to recalibrate it and load different parameters.

It is educational to take apart a broken device and look at how the touch screen is laminated to the cover glass.  (Be careful, when gorilla glass or dragontrail break, the shards are really sharp.)

The most likely scenario for failure in a device where you have a wandering touch is the conductor for one of the shifting axis is failing.  For example, if the touch is shifting side to side, then plating or conductor for a vertical region is failing.  Like many things in screens, it is not really possible to fix without really expensive equipment.  And often not even then.

 

[amyk]

The most interesting documents are in Chinese and from the manufacturers of these touchscreens/touchscreen controllers... look up "FTS touch panel design guide" and "FTS touch panel train" for some examples of these.

[Alex Eisenhut]

Get a free app that tests the touch screen like "multi touch benchmark" for Android, if IPhone I bet they have apps like that as well.

What app? Just turn on developer mode you'll see the focus spots.