Puck.js HRM

[edwardgalligan]

I've been reading this thread on Bangle.js HRM support. Given all the info I've read there, & that the support for VC31B + blobs is in Espruino (in a relatively non-Bangle.js-specific way - e.g. hrm_get_hrm_info) - I'm trying to get a sense of how viable would it be to put together a sort of "Puck.js HRM" with the VC31B.

I understand VCare is a Vietnamese manufacturer that doesn't seem to sell through consumer-facing channels, so sourcing hardware may be difficult.

Thoughts/questions

• if VC31B were attainable, I presume this would need a custom PCB with Bluetooth Beacon Kit - this isn't something that could be worked into puck.js itself.
• using an alternative consumer-available HRM modules would require working some support into Espruino & recompiling it.

Am I missing anything here or incorrect on any assumptions?

[gfwilliams]

We do actually have JS modules to handle interfacing to heart rate sensors already - which are more readily available):

• https://www.espruino.com/BH1792
• https://www.espruino.com/MAX30102

The MAX30102 one even has a link to ebay where you can buy the modules on breakout boards, which you could wire to the Puck.

Having said that, those modules only give your raw IR data and the algorithm is up to you. You could:

• maybe feed it into the VC31 binary algo
• use the 'open' version that's also in the Bangle.js repo
• Make your own one - Espruino has FFT built-in so you could just run that over it to pull out the main frequencies
• Feed the data to a PC/some other device where you do the number crunching

There are other concerns though - you need to package the sensor up so you don't get light bleed, have a way to hold the puck onto your wrist (there is a 3d printable case for this) and then battery usage could also be an issue.

All told IMO you'd have to have a very good reason to want to use a Puck over a Bangle.js which does it all for you :)

[edwardgalligan]

Feed the data to a PC/some other device where you do the number crunching

This would be ideal for my use-case tbh. given that what I'm looking for is a passive/zero-interaction/screenless data collector that can be compiled into reports later. Thanks for the links.

Battery usage could also be an issue.

Curious about this in contrast to Bangle.js - my instinct would've been that the screen would be a decent % of usage normally (even on standby). & it also bundles other components that this would omit. Aware I may be misjudging consumption of a lot of aspects though.

IMO you'd have to have a very good reason to want to use a Puck over a Bangle.js which does it all for you

My main motivation is form factor & not wanting "it all". What I'm essentially thinking about is an open / hackable alternative to things like the Polar OH1+ or the Oura.

All that said, I do realise puck.js is not significantly smaller than bangle.js (36mm x 36mm x 12.5mm -vs- 36mm x 43mm x 12mm) so the benefits here are likely to be pretty marginal.

[gfwilliams]

I'd definitely give the Bangle another look then!

The screen is a special 'memory LCD' that draws basically no power when on - it's a few millionths of an amp. And the extras (barometer, compass, GPS) don't really draw any noticeable power when not used. With the HRM enabled, that's the majority of the power draw (which'd be the same on the Puck too), but it's not such a big deal with the Bangle because you can just recharge it rather than having to swap the battery out.

While there is stuff you don't need, I get them made in enough quantity that realistically it's probably still cheaper to get a Bangle with all that stuff than to try and make something yourself. I guess PineTime could be a cheaper option too (although the screen on that, if enabled, really does draw a bunch of power).

The Bangle itself only has the reverse engineering open (the design itself is closed), but when I do finally get a Bangle.js 3 made I have plans to have that entirely open, and hopefully whatever you do make will 'just work' on the new one.