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[T] 3.5" Screen PPI

A project log for Tetent Timespy [gd0136]

A wearable PDA / smartwatch with a Tetent [gd0090] based input layout.

kelvinAkelvinA 08/09/2022 at 05:540 Comments

So I'm modelling the concept and I'm looking into what the actual dimensions of the panel is. I didn't find that, but I did find out that the 3.5" screen is probably some of the oldest OLED around.

I was wondering why the contrast ratio seemed awfully low for an OLED panel.

The 3.26" screen has the expected high contrast, but I don't think I'm going to be able to cut 6mm from the length or 3mm from the height because of how tight everything already is.

Yes, I know that this watch is going to look more like a sci-fi prop or a cyberdeck. This Hack Chat notification about the latter is partially a reason why I considered documenting this project.

The good news is that the seller of the 3.5" display also has a 3.47" display. The bad news is that it has a lower resolution. 

The good news is that it has a useful feature that sounds like it could be used for AOD.

I can't find contrast ratio or model (oh wait actually it's a AMS347FF01), but I have found this little announcement article from 2011:

Also, I though 198ppi was good, but then I checked the ppi of the low resolution 1.54" screens found on earlier android watches:

A crisp resolution for this size was 320x320px:
Perhaps it was Android making things blurry on the 240px screens (similar to DPI scaling issues on Windows), but the 480p OLED would look crisp in comparison to the 360p one.
Not sure where the listing is getting 198PPI from. Both screens only get 300cd/m^2 so visibility outdoors might be questionable. Hmmm decisions...

[about 5 minutes later]

I just found out that the 360p AMOLED was used in the Nokia N8 (source), which makes me think that it was the same OLED used in the Nokia E7 which I own (because I wanted to take notes with it, but working with only 2 thumbs is slow, hence #Tetent Tiny [gd0040] ), and if that's the case then the low power mode makes sense because the Nokia E7 had an always on display and was some of the best in OLED technology I've ever seen. I heard Nokia put some coating on the screen for even deeper blacks, but citation is needed.

Ok, if a 4" screen looked fine on the E7, a 3.47" of the same resolution should look even better.

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