I have the Adafruit Capacitive touch shield (1947) and I am having an issue with the FT6206 library I think and the way that it handles touch. I have posted on the adafruit forum and wanted to post here for more visibility.
Fire up the CapTouchPaint demo from the FT6206 and open the serial monitor.
You can draw with one finger with typically without any issue, seeing the touch coordinate registered. However, introduce a second finger and you will see the registered touch jump to (240,320). Even when you release, it still registers touch at (240, 320), and it locks up the whole interface and you can not do anything until you reset it.
I see in the Adafruit_FT6206.cpp file there are some notes about in theory it can detect two points but they can't share the same half of the screen. Sometimes, when your two fingers/touches are close enough it seems to take midpoint, but spread them far enough apart and the whole thing locks up.
No big deal for the paint demo, but sometimes when you release your finger, or hold a single touch point with one finger, it can happen as well.
Can someone smarter than me figure out what's going on here and how to avoid it? Can we avoid this issue in the code or os this a library level issue? Other?
Turning on the debug mode in the FT6206 library and watching the serial monitor this is what shows:
Again, sometimes it will show one line of "# Touches: 0" after releasing from a valid touch point.
Sometimes, this will cause it to endlessly cycle the "Touches: 0"
The easiest way to to replicate, is to hold a finger on the screen, then introduce a second finger onto the screen and that is a pretty surefire way to get it to have the loop issue. It seems you can get it out the loop state similar to the way it entered, by touching multiple points and releasing, and with a little luck, eventually it will go back to normal.
However, this is a problem when trying to navigate between UI pages on the touch screen and the whole interface locks up.