PiTFT Jumpy Cursor Moderators: adafruit_support_bill, adafruit

[antsar]

Just received a new Raspberry Pi B+ and a PiTFT (capacitive version) and assembled them. I installed the Raspbian image provided on Adafruit (pre-configured for PiTFT), selected 'boot to console' in raspi-config, logged in, and ran startx. The display looks great, however the touchscreen is unusable because the mouse cursor spontaneously jumps all over the place (even when I am not touching the device). This happens with no additional accessories connected, powered from a wall wart USB power supply. Reimaging the SD card did not help. The SD card is brand new, and Raspbian functions perfectly fine otherwise. Is this expected behavior?


Video: https://vimeo.com/108461064

Thanks in advance for your help.

[adafruit_support_mike]

That's not how it should behave.

Try reseating the flex cable in the connector on the bottom of the PCB. There are a couple of black tabs on either side that you pull out to release the cable, then push back in to clamp it in place.

If that doesn't do any good, post a photo showing your soldering and we'll double-check the joints to see if there might be any clues there.

[antsar]

The behavior is identical whether the PiTFT is seated directly on top of the Pi, or connected with a ribbon cable as shown below. Leads me to think its not the solder joints since its unlikely I would've screwed up the same pin exactly the same way on both connectors.



The intensity of the problem seems to vary over time - I tested it last night and was impressed because the cursor only jumped once or twice in ten minutes. Today, however, its back to skipping all over the place many times per second.

I've also checked the ribbon cable connecting the LCD to the board. It seemed to be slightly angled out, so I corrected it. The problem remains with full severity though.

Looking forward to any advice you can give.

Thank you.

(Edit: more pics. click for hi-res.)

[adafruit_support_mike]

Your joints look fine, but the change in rate leads me to think it might be something environmental.

Did you remove the protective film from the TFT? I see some air gaps along the edges of the display in the first photo.

[antsar]

The film is still there (hence the air bubbles), but it doesn't seem to be the cause of the issue. I booted up the Pi this morning and it was behaving perfectly, for about 5 minutes. The cursor wasn't jumping at all, and it was very responsive. I removed the protective plastic, and the problem ironically came back seconds later. I had noticed this pattern before too (works fine for a few minutes after boot, then begins acting up), but its not consistent. For example I just powered it off and back on, and the problem began immediately after loading the desktop.

[adafruit_support_mike]

Okay, when the going gets strange, the strange roll up their sleeves..

Try rubbing the screen down with a fabric softener sheet. Sounds nuts, I know, but the symptoms you're describing sound like they could be the result of an electrostatic charge building up on the screen. Dryer sheets are the cheapest and most readily available source of ESD-dissipative coating you can find. Used ones are actually better than new ones fresh from the box.. they're more pliable and they still have plenty of coating material left.