Reddit user DasBraadwurst is making a very cool led ring for mounting on guitar pedals. He showed a screenshot of his circuit and it seemed to have a very small controller on it. I inquired about it and he was kind enough to tell me: It's the Lumissil IS31FL3728 I2C LED matrix driver.
It measures 4 x 4 mm so it's perfect for my led dials. It drives up to 8 x 8 leds, so it's still a bit of a waste to use one per dial, and it does have an issue with addressing (it can only be set to four different ones) so I need to figure out if it is possible to switch address dynamically and just "enable" the one I need to write to (Address is set by connecting the address pin to Vcc/GND/SDA/SCL. Perhapsone could switch between vcc and gnd?)
The chip is available at jlcpcb (C2678860) at a price of $0.62 in quantities of 100, though right now they only have 80 in stock:
https://jlcpcb.com/partdetail/Lumissil-IS31FL3728_QFLS2TR/C2678860
Interestingly enough, jlcpcb as another matrix led driver available, the IS31FL3729 (C2940549), which is a 16 x 8 chip - but they have more in stock and it is actually cheaper ($0.58 @ 100), so perhaps it's worth giving a try.
For comparison, the STP16CPC26 constant current led driver shift register is more expensive ($0.73 @ 100). However, it IS less specialized, meaning it can be replaced if replaced. With the IS31 I would have to come up an I2C version with similar addressing.
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