4D Systems LCD 4DCAPE-43T Touchscreen jitter

While upgrading my Beaglebone Black with 4D Systems LCD 4DCAPE-43T to Debian 8 I discovered that the touchscreen wasn’t working anymore. Digged a day through software with no result. Then I was checking hardware and found interferences on the 4 analog signals of the touch screen, that were obviously caused by the LCD driver. A internet search brought up this post: BBB and 4DCAPE-4.3T cursor jumping. So I gave this 1nF capacitors a try and finally the touchscreen on that LCD is working rock solid.

A sure indication of the problem is that ts_calibration from Debian tslib isn’t working and reads “Took 1 samples…” for all 4 axis. Also ts_print_raw shows readings while not touching the screen. Continue reading