An anonymous DIY tech creator who posts hardware mods, zines and videos, including Casio watch mods and Raspberry Pi projects.
Commenters like the site's design and production quality, call the mods easy to pull off, and point to the creator's YouTube channels and print zines.
> The CM might only make sense for large volume products.
I'd also imagine products with hard physical constraints, either from connector placement or size alone. For example these fairly popular diy portable pi projects that seem to pop up here and there
http://blog.parts-people.com/2012/12/20/mobile-raspberry-pi-computer-build-your-own-portable-rpi-to-go/ could be a lot smaller
or
https://n-o-d-e.net/terminal.html where the first step is to strip the connectors away to fit the profile
n-o-d-e (blogger) has published many mods for this watch, with videos included. They have great production quality, and the mods are easy enough to pull off. https://n-o-d-e.net/casio.html
When I did this mod, I soldered the LED on its side, so that it shone directly onto the LCD. This made the watch face much brighter.
On reflection, the similar variant of the watch with an EL display is vastly superior. The A168 is similar to the A158 you mentioned but with a better light.
On an earlier page[1] the author mentions that they at one point "designed a more complex backplate which included […] a built in micro SD card reader, that you could read directly by plugging in a micro USB cable", among other things. Unfortunately, they go on to lament that this made the watch comically thick. As you say, the strap might be a good place to cram a USB interface without bulking up the watch body.
[1]: https://n-o-d-e.net/datarunner.html
They also have techno-optimistic YouTube channels that I love. There haven't been any new videos for a while, but some of the older ones are worth watching:
https://www.youtube.com/@NODEtv/videos
https://www.youtube.com/@MOSFETnet/videos
I think all of the videos have a written version on https://n-o-d-e.net/ for those who prefer that style of content.
Cool project. Tip: acetone will readily dissolve the plastic parts of the card leaving the antenna(s) and chip intact. I believe a few other people have made drop-in PCBs with NFC antennas. Here’s one: https://n-o-d-e.net/datarunner.html
Also, no F-91W thread would be complete without a mention of the sensorwatch project: https://www.sensorwatch.net/
If you want to explore even more treasure troves, here is a bunch of other hardware-related blogs you'll probably enjoy:
https://www.bunniestudios.com/
https://spritesmods.com/
https://dmitry.gr/ (has some insanely huge reverse engineering projects)
https://n-o-d-e.net/
https://ch00ftech.com/ (no updates since 2017 though)