Diy i2c bus board


I’m working on an i2c bus board to connect my er-301 to my white whale via i2c. I cobbled one together that resembles this:

I used a 3.3v regulator and 2 2.2K resistors, and I think everything is wired as it should be.

The voltage that I’m getting out of the regulator is ~6V (half of the 12V going in). Is this what I want? If not, any guidance as to what to do?



No. A 3V3 regulator should spit 3.3V out of its output. 6V is very wrong, and will lead to bad things with I2C.

When you say ‘resembles’ - what do you mean? You made your own layout? You implemented this circuit on a stripboard? It’s unclear - can you share the schematic of the circuit you made?


Thanks! That’s what I thought. I looked at the board on oshpark and did my best to replicate it on perf board. I will draw it up later today after work. Maybe I got a dud regulator? Thanks again!


I doubt you got a dud regulator. What part number did you order?

Replicating a layout on perfboard based on a PCB layout is risky. It’s easier to go from the original schematics, which are available in EAGLE format in @tehn’s repo, or I can make you a PDF.

Either you’ve got a 6V regulator or, perhaps, you’ve made a voltage divider with the pair of resistors.

I’m really trying to understand the layout you have, though, so when you’ve drawn it up, I can take a look.


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 :confused:

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)


I think it’s my poor adaptation of the circuit.
I’m good at following directions in kits or soldering things to other things… this is beyond my bounds of competence.

Sorry for the lack of convention in this schematic


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!)


Here you go, @doublecoolbossman :

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.


Many thanks friend !