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

Wow, this is really cool!

My son just recently accidentally banged up my bangle on the playground, so I thought it would be nice to have something to ruggedize the watch before it's too late.

Since I don't have the same dedication as halemmerich to transplant the whole watch, I though about creating an outer shell for the current watch housing that reduces risk of the screen getting deep scratches or cracks.

@halemmerich, from your experience, do you think that a shell with 1mm thickness around the outer borders of the watch would work? Something that could then be attached to the original housing using some glue, maybe?

(That reminds me, I should also share some of my original designs for a charging pedestal that I 3d printed for myself!)

I should add that we do sell https://shop.espruino.com/banglejs2-cover if you want something easy - but those are silicone, so might not be as protective as something solid

Thanks for the hint, @Gordon!

I'm not entirely sure (and I can't really tell from the pictures), but to me it looks like the silicone does not really extend above the glass that much and that's what I'd like to better protect.

If anyone has a better picture with the silicone cover on from the side, I'd be much obliged!

I converted the Step file of the banglejs housing (thanks @Gordon) to an obj that which I imported to fusion 360 to create the metal cover rim that fits around the BJS2.

I just finished printing the plastic sample and I'm quite happy with the result, even though the white certainly ruins the look, but that's just the filament I currently have loaded into my 3d printer... So I also did a render in fusion 360 so I could have a better idea what the metal part would look like.

Since @halemmerich mentioned that the part tolerances are good but might be a tiny bit off, I'll just order multiple pieces at 95%, 97%, 100%, 102% and 105% scale and check which works best. (For cost reduction, I'll try to order a single item that I have to saw apart, let's see if that works)

2 Attachments

I have given the border around the display an additional 0,5mm in x and y direction in my drawing and it fits loosely in the case. I did not try to measure that with a feeler gauge (lost those somewhere) but there seem to be about 0,3mm space all around the display so I would suspect you can be closer around 100% size for your tries. Maybe 101% and 102% to leave a bit of room for glue if you have your current CAD at a perfect fit. Since the turnaround is just about one week (JLCPCB->Germany) and postage is not that bad a second try is not a big problem.

If this fits well and works nicely with Bluetooth and GPS you could think about removing the original watchband holders and modeling them on the case. There are some people having broken those off and having them in steel is probably more rugged.

My attempt at having them print a connected part to try multiple sizes failes, as connected parts are not allowed for metal prints. Anyway, I now ordered a single one: I remeasured my actual watch with a caliper and added 0.3mm on all sides. Fingers crossed it fits!

@halemmerich I really like your idea of adding watchband holders to the metal part. This would require people to remove the original holders, but could also be a much cleaner design. If this fits nicely I'll add the holders to the CAD model and provide it for everybody to print/order themselves. It could also be a very simple and cheap way to repair broken BJS2s

That's a really elegant solution to the ruggedness problem. If it weren't for USB-C and a bigger battery that I want I would definitely go down your route. Doing the full transplant is very time consuming and the risk of killing the donor bangle is considerable.

I finally received the 3d printed metal part and it fits perfectly, a slight press fit. With a drop of glue it should hold on fine for day to day usage.

If the wrist band holders would also be made of metal and part of the cover, there would be no need at all for any glue, since the watch would stay sandwiched in place between wrist and watch-cover.

Anyway, I'm trying to figure out if I leave the finish as is, or if I should try to brush the metal using a Dremel bit on my small CNC... I don't even know if there is any pretty finishing to be achieved with the printed metal parts. Please tell me if anyone has any ideas

1 Attachment

I sanded it down a bit and it looks much nicer now. I got to keep sanding, bit I only have 120 grit paper right now. it still has the look as if Tony stark made this in a cave... But also maybe that is exactly how a banglejs2 is supposed to look

1 Attachment

Wow, that's awesome! I guess if you just ground off the Bangle's existing strap mount lugs then you could do them as part of the print without bulking it up too much?

The stainless is relatively soft and thus sensitive to scratches. I think the somewhat rustic optics you have now should withstand use pretty well. Could be nice combined with maybe band from wooden elements.

How is GPS, BT and touch for you?

i cant buy on your site because no shipping to my country.
how can i buy this ?sale on aliexpress or adafruit site (can send only to coumtry but i prefer aliexpress will much more cheap)

Haven't tried gps yet, but touch and bluetooth work flawlessly thus far. IDK if there's a Bluetooth benchmark of sorts that I could use to get any measurements instead of anecdata.

I'll try and order a new version with thinner outer walls and als wrist band holders.

All in all I am very happy with the outcome. It doesn't only make the watch more rugged, but I really like the style (and I even like the considerable weight it adds... It feels more "valuable")

Anyway, I'm on the phone now, but I'll provide STLs for anybody who want to order some covers themselves soon

Hi I would like to order those could you upload the STLs?

Hey @Poolitzer,

Sorry, I did not check for any new messages in the forum. Here's the STL of the current cover design.

I ordered it on jlc3dp.com using SLM 316L steel manufacturing. It cost 8$ + shipping and fit pretty much perfectly as is.

I will try to make a new design that also has wrist-band holders and a little thinner walls (currently I used 1.5mm, and I'll try to go down to 1mm) in the coming days.

1 Attachment

• bangleshell_v3(1).stl

Ah I will wait for that then, keep us updated. Thanks for the file though!

I completed the watch cover with thinner walls and the wristband holders. I've ordered one, but I cannot guarantee that it'll turn out fine, especially with the small holes for the wristband.

@Poolitzer if you're feeling lucky, you could already order one, but I'll be able to tell you if this works out in about a week or so, when the part arrives at my place.

2 Attachments

• bangleshell_wristband.stl
• 

Woawh that looks like annoying to design.

Im happy to let you try it first, if it doesn't work out I can order the first modified one and you could wait if that turns out fine on my end then :D

Since I could not get the watch built in the mark 2 case I have ordered the third revision. Mark 2 had the problem that it completely turned the order of things on its head. The display goes first and then everything need to be assembled (and soldered) the "wrong" way around.

To alleviate that mark 3 is designed to allow building on the base plate and then put the top including the display over it to be more similar to the original construction. I ordered in nylon SLS in to get similar precision as metal SLM but much cheaper prototypes. Surface is a bit rougher than SLM but overall quite good. Even very thin walls worked out mostly fine. Still some fine tuning needed but it seems get close.

Now I "just" need to assembly it into a working Bangle :)

4 Attachments

Oh I understood from Mark 1 you just pressed it on. So for this version you need to dissemble the plastic body and reassemble it in the metal body?

Then I would order Mark 1 I do not trust my soldering skills to do this without breaking the watch :D

Sadly this will always need disassembly of the original watch. There are 3 main points which are common to all my versions and were solved by soldering:

• USB charging -> Connect USB port to charging pads
  
• Other button -> Connect new button to mainboard
  
• Bigger battery -> Replace the original lithium cell
  
  

The button is actually soldered to a bit of flat flex cable taken from the backlight LEDs of a broken Bangle display.

I would say what I am doing has a very high risk of killing the donor bangle. Not quite sure if it is actually worth doing. It currently is more of an experiment just because I (maybe) can ;)

I have never designed flat flex cables, so maybe that would be a way to at least remove the most difficult parts of the soldering job, but currently it is definitely at the absolute limit of my abilities.

The design by @devsnd will get you the best way to get a more rugged Bangle. I will order one as well since my design is not close to be a daily driver.

As for progress:

• Everything can be mashed in the new case
  
• Button works
  
• HRM fits perfectly
  
• Bigger battery fits and charges via USB-C
  
• Flashlight dimly works (two LEDs driven directly by 3.3V from board because I do not have a matching value resistor and one LED burns out instantly)
  
• Not yet glued together
  
• No way this holds together in daily use, at least the solder joints will probably shake apart in a short time
  
  

5 Attachments

Omg you arent devsnd I confused you two Im sorry

The botched button flat flex could not take the abuse of soldering thick solid core wire to it, so I had to make my own... Thankfully that wasn't too hard, some kapton style tape and a bit of copper tape does the job just fine.

@Gordon is there a better way to get power to the LED than the 3.3V "testpoint" on the board? The plan is to use one of the LEDs with a resistor in series to get to 20mA. I noticed LED+ and LED- written on some points, can those be controlled in software and maybe deliver a current without needing a resistor in series?

3 Attachments

The flashlight is a great idea! I don't think there's an easier way to get at the LED than the 'LED' pad. Those will be connected to the backlight, and the only control we have is on/off - they go via a FET.

I'm not sure 100% but the LED pins will have their own resistor as they are for the backlight, but if you're lucky, it might be that LED- is a FET to GND, and LED+ is the resistor - so to attach your own LED you can ignore LED+ and connect your LED and resistor between LED- and VBAT.

There is another option...

On the PCB there are UARX/UATX pins which are unused and brought out to pads (https://www.espruino.com/Bangle.js2+Technical#gpio). You could buy a surface mount FET device in something like a SOT23 pack, then scrape a bit of the solder resist off the PCB near UATX (under that is a ground plane) and solder the SOT23 to the board - and then you can connect a LED via a resistor to VBAT and you've got pretty much as much power available as you want.

oh wow I love the idea of the extra button hack one thing that I really miss from the bangle1 on the 2 is extra tactile buttons. I think you can make much easier to navigate user interfaces that way.