It’s STM8, not STM32, which is why you can’t just do USB serial. STM8 is very barebones and cheap.
I think Adafruit now actually sells cables of the right type or very close: https://www.adafruit.com/product/4722 Only five years after I needed one :) I never had one of the original STM programmers, and I did the second firmware revision. I personally did both the “add a connector you have” approach in the guide, as well as bought some cheap 1.25mm/1.27mm connector pairs on eBay and filed them down until they fit. (To be honest the Adafruit ones look like the ones I have - so some filing might be required.)
The legit STM one with the cable isn’t too expensive, honestly, so if you might use it for something else later, just go for that and save yourself the hassle.
It's a hard one to find a replacement for, at least from other mice. You can make it work again for a while by pressing it down extra far when it's disassembled like this, (presumably cleans the dodgy contacts) but that gets to be annoying pretty quick. I eventually replaced mine with a Microsoft intellimouse classic, though I've read that the middle click in some of the Logitech mice are nice and robust if that's a button you use a lot like me.
This also works on the 990Cse Professional, with only minor tweaks, which I’ve added in comments. I suspect all the 900-series deskjets (at least those that use the 45 and 78 cartridges) are pretty similar.
On my 990Cse I had to remove a pink screw from the top of the power board to do this step.
IMU is the BMI055
FYI, I finally made some corrections to this teardown (it’s BNO070 not the related but different-sensor-fusion BNO055, the lenses only resemble Oculus DK lenses because they aren’t Fresnel, but they’re actually crazy looking two-lens systems related to this previous design, the “empty headers” aren’t unknown, some are even labeled). Left as much of the original spirit of the thing as possible without having inaccuracies in it. So, until it gets approved, the more complete version will be listed as an “unverified revision”.
No chips in the cables.
I think the connector is actually an "ERNI" connector, as in the company ERNI that makes the MicroBridge 1.27mm pitch connectors.
does the save here save a hex with all the tabs' contents, or does that just save the current tab? the UI is not very good, it's hard for me to tell, so I tend to save each tab.
(Oh, and FYI, I've got some other folks who I've suggested add to a guide or start a guide similarly, so don't be surprised if you see contributions roll in :D)
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