I double checked the regulator. Oddly enough, the first one I used was unmarked (whoops), so I swapped it out with another from the same package (which was marked 3v3). I got the same result, and after looking at what I did, I’m fairly certain I just made a voltage divider
I would appreciate the PDF! I will draw up what I did real quick.
it sounds like the pinout of your regulator is probably different than the one i used. regulators are rarely drop-in replaceable. check the data sheet, make sure your IN / OUT / GND make sense. (i’m sorry if this is too obvious, just double checking)
D’oh, I should’ve looked at the datasheet.
Because I got a through-hole voltage regulator, I looked up a pin-out for that (assuming they were generic), but I did not look up the specific regulator I used (turns out the pin-out is different!)
This is part of the schematic: the two eurorack power headers, the voltage regulator, and then the I2C lines, with the first three I2C headers (the rest of which just continue with the same connections).
As you can see:
the regulator is tapping 12V in from the Eurorack power and emits 3V3 out.
The 2k2 resistors are pullups on the 3V3 lines to the I2C connectors.
On the I2C connectors, you can see that pins 1/2 are GND, and then pins 3/4 are connected, and pins 5/6 are connected.
I hope this helps a little. I’m pretty sure you managed to make a voltage divider across the 12V out, previously.