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several unsensitive 2.4" TFT screens - older ones are fine
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several unsensitive 2.4" TFT screens - older ones are fine

by Monsterz on Sun Jun 13, 2021 12:27 pm

Hi - I have been using the 2.4" TFT with resistive touchscreens for a couple of years,in the same design, essentially, and except once a year ago they always worked fine. I bought another four or so recently and I find the touch screens are almost completely insensitive to pressure. When I just plug in an older one, it works great. I modified the touchscreendemo for my pins and also to display every read, and I see that the new ones require uncomfortable pressure and then they give semi-random pressure readings even if I keep it constant pressure. I am posting scren shots comparing old and new performance. There are different date codes on the IC's but the PCB etc seems the same rev. Has something happened? I'm thinking I'll convert to capacitive but that's a problem because I have a lot of gizmos already machined up to take these displays. Can you re-test them if I send them back, or replace with a different batch? Thanks!
Attachments
display that works.PNG
These have always worked very smoothly for me in the past. I was lucky I still had one to verify this with.
display that works.PNG (71.12 KiB) Viewed 212 times
display not sensitive.PNG
I've gone thru four brand new displays and a/b with the old one and it's definitely the touchscreens working badly
display not sensitive.PNG (70.05 KiB) Viewed 212 times

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Re: several unsensitive 2.4" TFT screens - older ones are fi

by adafruit2 on Sun Jun 13, 2021 10:08 pm

whats the exact part number?

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Re: several unsensitive 2.4" TFT screens - older ones are fi

by Monsterz on Mon Jun 14, 2021 6:35 am

Part number 2478. Two bags say W11732-A on the bottom. Another says W7119-A. Other bags are not currently found.

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Re: several unsensitive 2.4" TFT screens - older ones are fi

by adafruit2 on Mon Jun 14, 2021 12:26 pm

ok 2478 - we think the touchscreen overlay did change a little however it still passed our test. do you use a stylus to press on the touchscreen?

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Re: several unsensitive 2.4" TFT screens - older ones are fi

by Monsterz on Mon Jun 14, 2021 8:38 pm

Yes, I put fairly tremendous pressure using a plastic point. The performance is dead to the extent that I'm sure 100% of people trying to use them would say that they are broken. It's only by tweaking the code to allow any nonzero pressure and no maximum, and pushing with dangerous force, that I was able to determine that they were working at all.
I did in fact notice that the nomenclature on the overlay was different but I didn't see any correlation in that. I compared the boards and they look the same except for date codes on the IC's and the white lettering near the Underwriter's stamp. That didn't correlate either. But in each case my sample size (1 good unit, 4 recent bad units, and 1 historical bad unit >1yr old) was very small.
Can I please send them back for some partial credit or replacement? I think you could donate or use them as displays only, or maybe you can fix them but of course there's solder (RoHS ok) on the jumpers and the ten pads on that side. If you have anything I can do to try to fix them I'll give it a go, just let me know what to do.

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Re: several unsensitive 2.4" TFT screens - older ones are fi

by Monsterz on Tue Jun 15, 2021 8:42 am

Regarding the testing of these, I was in fact taken aback to see a deep swirl/mark on at least one of the displays as I took it out of the bubble wrap, so I took a photo. Please see attached. So it's possible that they were tested but with the use of brute force which left a mark. Perhaps the test should be done with a pre-determined length of rubber rod (like an electric eraser insert) so that if you push at a 45 degree angle it should respond without the rod bending.
Incidentally
IMG_6498.JPG
IMG_6498.JPG (713.25 KiB) Viewed 160 times
, there seems to be a very defined "sweet spot" that at least functions when pushed hard, but there are some 'dead zones' that will never report a contact. So the test should be done at the center but also at the four corners.

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Re: several unsensitive 2.4" TFT screens - older ones are fi

by Monsterz on Tue Jun 15, 2021 8:52 pm

This doesn't seem to be getting anywhere. I will return them and hope for the best. I hope you find out what went wrong and why these touchscreens are so bad.

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Re: several unsensitive 2.4" TFT screens - older ones are fi

by adafruit2 on Wed Jun 16, 2021 5:30 pm

monster, you cannot return tfts that have been soldered to.
we test each board, as you see, by drawing on the touchscreen, the marking is on the plastic protector. dont remove that if you want to return the screens!
we're investigating, it will take a few days

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Re: several unsensitive 2.4" TFT screens - older ones are fi

by Monsterz on Wed Jun 16, 2021 9:28 pm

I have received a return auth for 3 of them but I will wait to hear back if you have any info on how I could make them work. They were tightly packed in their bubble wrappers and I wonder if the uneven pressure from the bubbles could have deformed the plastic layers as they sat for too long in that condition. If so, perhaps they need a cardboard between the face and the bubble wrap to make any pressure more evenly distributed.

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Re: several unsensitive 2.4" TFT screens - older ones are fi

by Monsterz on Thu Jun 17, 2021 7:29 am

I tried to make a mark on the plastic with wrenches of increasing weight and found that I need to use the full weight of a 1 lb, wrench to leave any sort of mark on the screen protector. The mark that I saw, coming out of the bubble wrap, was more intense than that, and it apparently persisted for the months of storage. I don't think the mark I made with the wrench will last like that.

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