(Maybe) Building a new case for Bangle.js 2

My rugged cover finally arrived! (I was a bit stingy on the postage this time, so I had to wait longer).

It came out great, I'm wearing it on my arm right now, it's a perfect fit. BUT the holes for the watch-band are a teeny-tiny bit to small, so I had to find the smallest drill bit (I used one from my small CNC) and used my dremel to enlargen the holes by a fraction of a millimeter, but then everything fits nicely. (Lemon for scale) So it's not perfect, I cannot recommend ordering it if you don't have the tools to enlargen the holes.

Other than that it's also a little less bulky, I reduced the wall thickness down from 1.5mm to 1.0mm (had to send a confirmation to JLC3DP, because they say the margins are too small, but as I said, it came out perfectly). Also I reduced height of the cover, the upper surface is almost flush with the screen, but not completely (about 0.5mm headroom), which is enough for most accidental bumps. (I cannot save the screen from cracking when direct force is applied in any case).

I still have to sand the surface this evening to make it look nice, which will take a lot longer this time, as there are more edges and angles. I am very happy with the result so far.

@Poolitzer If you have a small drill at home, you could go ahead and order the cover as is from the STL I uploaded last time, but I will also provide an updated version with a bit larger holes in the coming days.

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Wow this looks amazing. I can wait, I don't have that small of a drill xD

That's awesome @devsnd. We might be getting close to needing to change from "protecting the Bangle" to "how to protect stuff from the Bangle" :D What is the diameter on these holes? In nylon SLS 1.5mm is actually a tiny bit to big. Still functional but a bit wobbly.

Thanks for the infos @Gordon, lots of stuff to think about and experiment with. Especially the two free pads. Could I just put a button on each one to 3.3V without further hardware and do the rest in software or are there pull-up/down or current limiting resistors needed? Probably that's all integrated in the chip anyway but I don't want to fry it. I imagine using something similar to the three button control scheme of the first Bangle would be awesome.

you won't need pullup/down resistors you can control that internally on the gpio ports. You'd want to connect the buttons to gnd with an internal pullup.

That's looking great @devsnd!

Could I just put a button on each one to 3.3V without further hardware and do the rest in software

Yes! GND or VCC will work, but GND is probably more readily available as you can just scratch away at the solder resist almost anywhere on the PCB and get to the ground plane.

Very neat - and inspiring! ...especially the extra control and connectivity.

I have tested the bigger battery while wearing the prototype. GPS and HRM on always on got to well over 15 hours runtime. That's actually a bit better than I expected from the volume increase of the battery.
The next version will have space for two additional buttons. And somehow more space for the LEDs, since I botched the install by glueing the case shut before the resistors arrived. Those things are tiny... but at least it now works with usable brightness.
Trying to sand the surface of the nylon made it look grey and wouldn't get better by blasting with hot air to melt the surface. So it's probably better to not sand if not planning on painting.

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We might be getting close to needing to change from "protecting the Bangle" to "how to protect stuff from the Bangle"

True! Apparently the printed steel is almost as durable as CNC machines steel, so it's definitely absolute overkill. Maybe I'll make another STL with even thinner walls for those who want to dare ordering one.

What is the diameter on these holes? In nylon SLS 1.5mm is actually a tiny bit to big. Still functional but a bit wobbly.

Since the rest of the cover was really spot on on terms of size, I used exactly 1.0mm, but I should probably use 1.2mm or so to make it fit without modifications

I'm really jealous of your additional buttons: it's one of the features I listed in the banglejs3-wishlist-thread to be my favourite changes. A real flashlight is also a very cool addition, I keep using my phone for that, but I don't always have it on me. The flashlight could also be a great notification indicator for busy environments when the vibration might not be enough to get my attention (e.g. doing sports)

The flashlight is not connected to some controllable output, it currently just is powered by a 3.3V rail on the mainboard. Maybe a light connected in parallel to the buzzer would be cool for notifications. Since there are only two unused GPIO I will probably use those for buttons.

@Gordon is the pin numbering on this page: https://infocenter.nordicsemi.com/topic/­ps_nrf52840/pin.html?cp=5_0_0_6_0_1#qfn4­8 the same as on https://www.espruino.com/Bangle.js2+Tech­nical#gpio?
If so 42 and 43 seem to be analog inputs and I could attach multiple buttons to just one of those pads with resistor dividers to detect which one is pressed. So all the buttons I want on one pin and software controllable flashlight as well.

Edit: It seems those pins are not usable as analog pins. At least analogRead only returns NaN while digitalRead works fine. So short of an I²C IO expander or something like that the easy thing to do is 2 additional buttons.

I finally got to sanding the bangle cover and also to make the adjustments to the STL.

This time I sanded the cover with the dremel instead of by hand and it's much shinier than the first one. Anyway I really like it and for now I haven't encountered any problems with this design.

@Poolitzer the STL attached to this post has a wristband-holder hole size of 1.25mm, instead of the 1mm I had ordered. You should be able to give that a try and if we're all lucky, it comes out perfect for you, no modifications needed. Tell me how it goes!

Oh and by the way, if anyone wants to have the first version, without the wristband holders, I now have a spare one that I would send out for free. Whoever wants it, just tell me where to send it to. It fits perfectly on the bangle without modifications, but I always put a drop of glue between the bangle and the cover so it wouldn't get loose over time.

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• bangleshell_125.stl
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That looks great, definitely easier on the eyes than my concoction :D

Ordering it now thank you so much for providing them, will definitely give an update how it turns out.

Mk3 currently survives nicely as a daily driver and will now have to stand up to a hiking trip. Mk4 with a bit of tuning to the outside like the now internalized buttons has arrived and I will build it in probably two or three weeks.

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@halemmerich I'm afraid the numbering isn't the same, no. Basically:

• D0..D31 correspond to P0.00 to P0.31
  
• D32..D47 correspond to P1.00 to P1.15
  

Thanks, that then matches what I see when using those pins.
After a week of hiking there are casualties. The HRM seems to be broken. I do not know the exact reason but I suspect it to be either the glue at the HRM breaking down due to contact with sun screen and sweat or maybe the thin nylon at the bottom being a bit porous due to the SLS manufacturing. Maybe I can test that theory somehow with trying to press some water through with a syringe or something. If this is true I will probably need to do at least the bottom half in metal or coat it in epoxy from the inside to prevent moisture ingress.
Funnily enough the HRM survived multiple cycles of not working at some point in time around mid day while hiking with very low LED brightness still showing up and then seemingly drying up over night and showing believable results in the early morning with high LED brightness. Now it does nothing at all and its probably death by corrosion. Rest of the watch hardware seems fine, probably protected by the big battery over the HRM.

The SLS nylon definitely is porous. I put one of my prints into water and overnight it soaked through...

I'll try to coat it from the inside with something to get the prototypes more resistant but metal is probably the way to go. Maybe resin printing would be better as well but it really does not handle temperature well.

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Oh wow, thanks for the update - that's very interesting! I always assumed it would be ok. Maybe SLA prints would be better - they've got to be surely?

I wonder if (if you don't care about dimensional accuracy) you could run over it with a hot air gun and re-melt the surface to fill up any potential holes?

Maybe SLA prints would be better - they've got to be surely?

Pretty sure they are. Any remaining liquid resin inside the print should be cured after they blast it with UV after the print itself.

re-melt the surface to fill up any potential holes

I actually tried that after sanding one of the prints to get a better surface finish. Using a 630°C heatgun the outer edges melted a bit and became black and shiny but the flat faces did not melt before everything was so hot that it started warping. I think to be able to do this one would need a part with substantially more volume to have a chance to melt the surface without destroying the part. Or maybe freeze it beforehand :)
The way to go is probably a low viscosity epoxy resin that can seep into the pores or just painting it. I tried that with a solvent based clear coat and a metallic effect spray paint so the next prototype will show how that stands up to actual use.

Hey there, sorry to revive this thread two months later, but I really like this approach and am considering doing this myself. However, I'd like to use this opportunity to fix one of my major annoyances that I had when switching from my trusty old Pebble to the Bangle - the 20mm strap. So if I'm going to have new strap mounts anyway, why not make them 22mm ones like on my old Pebble?

Since I'm not an expert at 3D modeling and STL files are not ideal for being altered after the fact anyway, I'd like to ask you: Would it be easy for you to make a 22mm version of this as well? If that's too much to ask, could you maybe send me the original project file so I can try and figure out how to do it myself? That would be extremely appreciated!

Thank you for this amazing design!

I'm a bit short on time lately, but I got to tinker a bit on the Mk4 prototype. It is painted for improved water resistance but I don't like that a lot since it seems and feels cheap. Final one will probably have a metal underside and some sort of waterproof plastic for the top.
The last build was extremely fiddely because I had to solder on both sides of the board. So this time I have decided to move all soldering to the top side by using copper and polyimide tape as makeshift traces to wrap around the border. This will hopefully keep the internal cabling shorter at the cost of having to solder if disassembly is needed.
The "antenna" is also just a bit of copper tape to test out if a completely random antenna will work at least a bit in preparation to maybe using a full metal case as antenna.
Mk3 developed a bit of a flaky BT connection, probably caused by moisture ingress since the nylon SLS is porous. I will check that when the new one is ready, whenever that may be ;)

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@user159197 Here you go! I just had to make some parts of the model parameterizable and then it was easy to change the width of the wristband from 20mm to 22mm afterwards. This also includes the fix from my first try, with the slightly larger holes for the wristband mounting bar (using 1.25mm instead of 1mm holes), so I hope this works for you out of the box :)

@halemmerich, that looks really good! I'm starting to get pretty jealous of your 3 buttons and the usb-c port there. I hope airport security won't ask you to much about your watch next time you fly, though ;)

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• bangleshell_22mm_wristband.stl

Awesome, thank you so much!

I have taken the liberty of editing this thing a bit further. The wristband mounting points were not large enough in their new positions, resulting in some valleys between them and the main body. I also closed up the holes on the outsides.

Since all metal 3D printing services are either ridiculously expensive where I live or have long (and also relatively expensive) shipping, I'm probably going to fire up my resin printer and do a test print before pulling the trigger. But in the end, I'd like to have this thing in either blackened steel or polished brass. Maybe I'll get around to posting some pictures.

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• BangleCase_22mm.stl

airport security won't ask you to much about your watch

Haha, yes, that is probably worth a bit of consideration... Programming a microcontroller based temperature-control on a breadboard in a long-distance bus got me some peculiar glances of other passengers. 😂