There are several of those on this forum. One of the longest-running threads was
"Arduino Rotary Table for Dummies."
The late Chuck Fellows originally started quite a few of these projects a few years ago and the thread "Electronic Dividing Head using the Arduino" is good information and shows several variants made over a period of time.
My own version of a 5C indexer is included in that thread as post No. 250 in that thread.
Just enter those thread titles in the Search on this forum. CAUTION: Due to the time that has past since some of those the specific controllers were in common use there have been changes that will most likely mean you would need to modify your design and programming to fit what is on the market today.
The main point is that building an electronic indexer is not all that hard, but requires several different skills.
ALSO, there are now more versions of electronic rotary tables on the market you can buy. For Example, Grizzly sells more than one.
Let us know what you decide to do.
I stopped watching the thread before your post shoe, but I too followed Chucks lead and build a dividing head based on his scrips. I too chose a spindexer as my dividing platform, It was just easier when my milling skills were less than I desired. and when all I really wanted was to play with an arduino controller on a project that resulted in my than "hello world" being displayed. So a spindexer conversion seemed logical. I still have a screencap of one of my design iterations in fusion.
I was never happy with the lack of smoothness in my spindexer spindle, and I hadn't yet fully integrated the controller and power supply into a sealed unit when machining dust became an issue. Rather than fix the dust issue I dismantled the stepper drive and put the stepper and controller in a box somewhere for future use. I ended up pimping out my spindexer instead and made several additional indexing plates and upgrades ala OxTools method. I was only cutting a very limited set of gears so this was expediate, cheap and easy.
By this time cheap import options started arriving on the scene, and I'd also concluded that a simple dividing head only tool made little sense. Especially if you're making or buying a fixture with a good spindle and accurate concentric work holding ability to use as a base. Other controllers became plentiful, other electronic machining projects started popping up. That is when I stared planning to build a multi-purpose controller to control a rotary devise for milling, drilling, and grinding. It will utilize rotary encoders I now have mounted on just about every machine tool I have. Dividing, gear hobbing, cylindrical grinding with surface grinder will all be options.
Like Alton Brown, I too remind people, on the dangers of unitaskers cluttering our workspaces needlessly. So people, go forth, take the indexer idea but expand on it, make your project a multitasker.
I finally was able to pick up a Harig Ultra-Grind No. 5C-V that has capability to be motorized to use as the based for a project.