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Bent 7 segment display
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Please be positive and constructive with your questions and comments.

Bent 7 segment display

by floriancargoet on Fri Nov 08, 2019 9:30 am

Hi Adafruit,

I've recently bought the 1.2" 4-Digit 7-Segment Display w/I2C Backpack (https://www.adafruit.com/product/1270) and the display is a not straight. I took a picture of the display against a straight ruler and you can clearly see a gap of between 1 and 2 mm in the middle.

7segment.jpg
7segment.jpg (134.06 KiB) Viewed 144 times


While it probably wouldn't be an issue for most projects, it becomes almost unusable for mine. The display is supposed to be inserted in "blind hole" in a piece of wood. The hole is made with a router so that around 1mm of wood is left and the light of the display is visible through the wood. For it to work well, the display must be flush against the wood. If there is the slightest air gap, the digits are blurred. With the gap I have on this display, it's unreadable.

Do you have any idea how I can fix it?
I tried to insert a small shim but it's bending the circuit board instead of straightening the display…
Do you have a replacement program for this kind of issues?

Have a nice day!

floriancargoet
 
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Re: Bent 7 segment display

by millercommamatt on Fri Nov 08, 2019 10:20 am

This might just be how the displays are made. Look at the third product picture here: https://www.adafruit.com/product/1264

Note that it looks like there's a similar bow and I suspect there's some variance from the manufacturing process. You might have to do a lot of hand fitting. If you're willing to sacrifice a few for testing purposes, try putting some clear epoxy in the bottom of your hole to fill the air gap and better facilitate light transmission. Or maybe if you desolder the display you can undo the bow by putting some pressure on the display and then use some optically clear glue to hold it down in the hole. Or maybe you are just going to spend some time with a contour gage and some sandpaper.

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Re: Bent 7 segment display

by floriancargoet on Fri Nov 08, 2019 10:44 am

Indeed, the 3rd product picture looks exactly like what I have…
Thank you for your ideas!
I've never done epoxy so I think I'll first desolder it to test the flexibility of the panel and estimate the probability of success of the clear glue method.

floriancargoet
 
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Re: Bent 7 segment display

by adafruit_support_bill on Fri Nov 08, 2019 11:10 am

I have a few of them here and they all have a similar bow. It is most likely caused by differential shrinkage of the potting material used in manufacture.

Some good suggestions from millercommamatt. Another option would be to use one of the clear acrylic or polyurethane casting compounds to partially fill the hole. These are more liquid than most epoxies, so it is easier to eliminate any bubbles.

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Re: Bent 7 segment display

by floriancargoet on Fri Nov 08, 2019 11:23 am

Would it be stupid to sand the display itself ?

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Re: Bent 7 segment display

by adafruit_support_bill on Fri Nov 08, 2019 11:52 am

Judging from the overall thickness of the display, my guess would be that the plastic pieces that form the illuminated segments probably extend at least a mm below the surface. But I've never sliced one open to see.

If you do attempt it, I would do it slowly. Too much pressure on a belt sander could generate enough heat to melt the plastic and leave a gummy mess.

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Re: Bent 7 segment display

by floriancargoet on Fri Nov 08, 2019 12:02 pm

The gray plastic surrounding the digits is very thin and would disappear with the sanding. I don't know if it's only decorative or if it blocks some light.

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Re: Bent 7 segment display

by adafruit_support_bill on Fri Nov 08, 2019 12:34 pm

The dark gray color is at least partly intended to increase contrast with the lit segments. It may also serve to block stray light. I'm not sure what is underneath it.

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Re: Bent 7 segment display

by floriancargoet on Fri Nov 08, 2019 3:10 pm

I did a test with a spare single digit display and good news: under the black layer, there's opaque white plastic so it's all good. Now, I just hope I can remove 1mm without damaging the components inside.

1.jpg
1.jpg (158.06 KiB) Viewed 100 times


Let's sand the big display!
2.jpg
2.jpg (167.99 KiB) Viewed 100 times


Almost there…
3.jpg
3.jpg (163.66 KiB) Viewed 100 times


Next pictures in a another post since I can't attach more than 3 files.

floriancargoet
 
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Re: Bent 7 segment display

by adafruit_support_bill on Fri Nov 08, 2019 3:12 pm

That looks promising. You only have a fraction of a mm to go . . .

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Re: Bent 7 segment display

by floriancargoet on Fri Nov 08, 2019 3:15 pm

Now we can see it's perfectly straight.
4.jpg
4.jpg (173.14 KiB) Viewed 98 times


The big question is: does it still work?
5.jpg
5.jpg (161.12 KiB) Viewed 98 times


The lighter red areas are a camera artifact, they are not visible to the naked eye.
My issue is fixed! Thank you for your suggestions!

floriancargoet
 
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Re: Bent 7 segment display

by adafruit_support_bill on Fri Nov 08, 2019 5:10 pm

Nice to hear that worked out for you. Looking forward to seeing a photo of the finished project. :)

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Re: Bent 7 segment display

by floriancargoet on Wed Dec 18, 2019 10:46 am

@adafruit_support_bill : I forgot to post the requested picture when I finished the project! You can see it here (pictures + videos):
https://www.instagram.com/p/B5vh-XOoHRD/

The display is off until you press any button (my wife doesn't want it to light the bedroom), you can define 2 alarms with optional week-ends and choose between 9 MP3 tracks.
There's also a global volume setting, and a nap mode, where you can set up an alarm very quickly (1 button press = + 10 minutes).
Between the flash storage of the settings & the RTC battery, you can unplug the clock without losing anything.


  • Wood part: unfinished maple + oiled (linseed) european walnut
  • Electronic part: 7 seg display, a stack of Feather M0 + Feather Music Maker + Feather DS3231, some speakers and push buttons.
  • Code part: 1000+ LOC. Most of it is a big state machine to handle the settings menus and submenus: https://github.com/floriancargoet/feather-clock

Adafruit parts:

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Please be positive and constructive with your questions and comments.