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Apparently the nRF52840 already has NFC functionality
yes
that could be used to perform contact-less payment operations.
no, you need far more than NFC to do that. typical debit/credit card has secure CPU often with specific secure applications (possibly written in Java) uploaded by bank/visa/mastercard/manufacturer at card creation time
also check some answer here https://devzone.nordicsemi.com/f/nordic-q-a/18627/nrf52840-hce-as-a-payment-card or the picture in https://source.android.com/docs/core/connect/offhost-payment-sync - notably the UICC box there and/or read this https://trustedconnectivityalliance.org/wp-content/uploads/2020/01/NFCPaymentUICCConfiguration_v1.0FINAL.pdf (e.g. chapter 7)
EDIT: HCE in the first link IMO means Host Card Emulation - see also https://developer.android.com/develop/connectivity/nfc/hce
In the hopes that my voice for a next bangle shall be heard, I also have a wish list for what would make it an even greater device for version 3.
Sorry for the wall of text, you can read the conclusion for a TL;DR:
** Battery **
** Speed **
IDK what the bottleneck for the responsiveness of the watch is, but it would be awesome if it could be reduced. If there was a way to have a clock the CPU or memory faster just for launching apps, that would be awesome. The performance would be perfect if you could achieve full-screen smooth scrolling using the touch screen. If it was possible to have different power-states during active use and during passive use, the overall power consumption should not be much higher I guess, since race-to-idle can also be a way to save power.
** Screen **
** Environment Sensors and Water resistance **
Anyway, it would be awesome to keep it on when swimming or when taking a shower. Not necessarily because I need to check my messages in the shower, but rather because I'm often afraid to forget to remove it before.
** Buttons **
More buttons or a wheel like the apple watch would be nice. Even just a second button could make a big difference, but 3 would be perfect I guess. Having a touch screen still is great for building diverse UIs and input schemas for individual apps, but I I'd love to have some standard interactions - maybe similar to an android phone - mapped to the buttons.
** Connectivity **
IDK the details, but I think bluetooth has gotten much more stable over time (with firmware updates) and that's great. But still, sometimes I have disconnects for no reason. For all apps that do some background task periodically that require a connection, this is somewhat annoying. If there was a chance to have better bluetooth (chip/antenna/whatever), this would be pretty high on my wishlist. Maybe it's a phone thing, in which case I retract my statement ;)
Also it would be great if the watch had Wifi. I wouldn't want to use it all the time as that would kill the battery super quick, but I have Wifi available all the time when I am indoors and it would be great if the watch could then work more autonomously, so I could leave my phone at home. My bet would be that a bunch of people would build low-bandwidth server applications that work well with the watch and that would be awesome. (this could also nicely tie into the other espruino powered devices)
** Contactless Payment **
Apparently the nRF52840 already has NFC functionality that could be used to perform contact-less payment operations. IDK if this is a hardware/software/legal limitation, but if I could pay using my banglejs, I could leave my phone home a lot more often.
** Health Sensors **
I never use the heart rate sensor as I found it to be too unreliable. I would love to use when doing sports. Same for sleep tracking. I found the sleep detection to be lacking, even though this was one of the main drivers of me buying the watch in the first place! (instead of returning the device, I got hooked on the eco-system ;). Maybe I should give it another go, but the last times I tried heart-rate sensor and sleep tracking I was rather disappointed.
It would be great to have an hardware upgrade here for more reliable sensors. If I could wish for anything, then also a blood oxygen sensor would be awesome.
** Conclusion **
The BJS2 is already great as is. It strikes a great balance for many features. There's a few things I would love to see improved, but at the same time I see how improving some features could be at the cost of others (also considering small form as factor a feature!). So generally I rather like to see many small improvements on the current hardware, especially reliability and more physical inputs, than a large jump in a different direction, because many things are already in a great balance.