Gadgetbridge VS amulet-project

You'll need your band's auth key. More info

It did take time to set it up with the watchfaces I want, however it's been a set and forget type of thing and I haven't touched Gadgetbridge since except to change to my other Pebbles. It shows how to download watchfaces here https://github.com/Freeyourgadget/Gadgetbridge/wiki/Pebble-Watchfaces

When I bought my smartwatch I made sure that it is supported by gadgetbridge so my data doesn't find it's way to insurance companies in the future.

See here and click on each watch individually: https://github.com/Freeyourgadget/Gadgetbridge . I've had various mi bands and they work similar to the official app from a feature set standpoint but different layout. I haven't tried other brands but they are probably good too.

Check of the list of compatible devices for GadgetBridge https://github.com/Freeyourgadget/Gadgetbridge

I don’t know if this will help but I found this. Might be worth exploring. https://github.com/Freeyourgadget/Gadgetbridge/wiki/Pebble-Firmware-updates

You can add your own apps vi a patched firmware.

https://github.com/Freeyourgadget/Gadgetbridge/wiki/Amazfit-...

I helped design and have manufactured a smartwatch style health tracker as part of a research project:

https://amulet-project.org/

It cost somewhere around $200-$250 per watch in a quantity of 150 five years ago to have them made and we did final assembly (putting the PCB into the 3D printed case) ourselves, as well as testing. The MCU was an MSP430, there were a variety of sensors, microSD card, USB charging, an e-ink display, a Bluetooth LE radio that talked to a smartphone and external wireless sensors, and touch sensitive buttons/slider. This is the company that built them for us, I'd recommend them:

https://www.emeraldems.com/dataed/

They can help with design also, though I've only used them for manufacturing.

The software is available here:

https://github.com/AmuletGroup/amulet-project

Note that because the radio chip is often revamped the one we used is now obsolete, which also obsoletes the radio firmware. Some of the other parts have also become obsolete (chips go obsolete fast!)

That said I'd recommend hacking an existing smartwatch instead, they are really cheap and it is easy:

https://hackaday.com/2021/07/08/reverse-engineering-a-very-c...

https://hackaday.io/project/144350-hacking-wearables-for-men...

https://hackaday.com/2018/05/04/hacked-fitness-trackers-aim-...

https://hackaday.com/2018/05/29/hacking-a-fitness-tracker/

Designing your own system and board and making it reliable requires a lot of special knowledge. For example, did you remember to add anti-static protection diodes to all external electrical I/O? Does your battery management keep the battery from discharging to too low a point? If you have more than one MCU how to you synchronize them? How do you keep accurate wall clock time/date? How do you get data on/off the device? Where should you put test points on the PCB? What connectors are reliable? Does your Li-Poly battery need a protection circuit? Do you need it to be waterproof?

So designing something close to a product is not easy. It took us years and several very different prototypes and the end product was still a prototype (no waterproofing for example and not impact resistant). If you're just doing this for fun and are ok with something less polished or are interested in building a prototype, then by all means try designing your own, it is not too hard to get a working PCB and design a 3D printed case for it. You can find several examples of people making their own smartwatches on HackADay.com which might helpful.

I worked on a research project for several years (ending around 2018) using smartwatches to record a variety of physiological measures like stress. We were always looking for an open platform to use, and tried a variety of Android Wear watches and the Apple watch, but found little with the features we wanted. Microsoft used to make a smartwatch that had open access to almost all the sensors via Bluetooth, but they stopped making them some years ago. So we designed our own. All the design info and firmware source is available here:

https://github.com/AmuletGroup/amulet-project

This let us build a custom operating system that could run multiple apps and include external sensors via Bluetooth plus a few internal sensors plus a link to a smartphone (and it's sensors). Near the end of the project I had a bunch of them (125 I think) made by an electronics assembly firm. If you want to build your own those files might be a starting point, but I'd also add the warning that many of the components, particularly the nRF51822 radio/MCU are likely no longer available in that exact version (Nordic changes their chip design often) which also means the firmware would need porting to the latest SDK. The touch interface chip is now obsolete. To get 125 built I had to pre-buy all the critical components we needed (some of them off eBay) and send them to the manufacturer. The e-ink LCD panels were hard to find also.

You might be interested in this:

https://hackaday.com/2019/02/20/custom-firmware-for-cheap-fi...

That Arduino IDE generated firmware will run on a variety of cheap fitness trackers from China (the ones that use an nRF52832 radio/MCU). I haven't been active in this area for a few years so there may be new products available now. I see there are a number of self-built smartwatch projects on HackADay:

https://hackaday.com/?s=smartwatch

I'd also warn that getting reliable, accurate medical sensor data from a smartwatch or body worn medical sensor is not a solved problem. Unlike traditional medical sensors used next to a hospital bed a mobile sensor is subject to a lot of motion and environmental changes which messes with the readings. It's difficult to keep a sensor attached to one specific place on a human body. The more advanced sensors you'd like such as blood pressure are not available yet. Heart rate variability in Garmin's is usable, but wrist or body motion can throw it off. A chest strap such as a Polar H7 will give you a much better heart rate and HRV reading, but many people find them uncomfortable to wear. Blood oxygen readings can be fairly accurate when the person is not moving and the strap is tight, but will vary wildly once the person is motion. Be prepared to have to filter the data (e.g., throw out sensor data when the accelerometer indicates motion). Do a search for the new devices promising blood pressure (Samsung I think) or blood glucose monitoring (Apple). One of those might fit your needs when they become available. Beyond that have a look at medical web sites to see what hospitals are using (although those devices tend to require a prescription and are usually only sold to hospitals). You might find some leads here:

https://www.mobihealthnews.com/

There are some research projects in this area too, here's one of the big ones:

https://md2k.org/

led by Santosh Kumar:

https://www.memphis.edu/cs/santosh-kumar/mhealth-systems-lab...

Deborah Estrin has done a lot of excellent research on mobile health sensing as well:

https://en.wikipedia.org/wiki/Deborah_Estrin