I'm trying to design around Sparkfun's I2C products to work with Adafruit sensors, specifically Sparkfun's I2C Multiplexer, Differential Endpoint, and Differential Midpoint. From what it looks like, Sparkfun's schematics of their devices are based around 3.3 volts. However, is it also possible to run off of 5-volt logic as well?
Based on Sparkfun's schematics, if you start with an endpoint, you bring in power through their header at VCC, which depends on the I2C voltage that your MCU operates at. A short on the endpoint would pass it to the Blue wire on the RJ-45 line. From there, it can go to another endpoint and receive the same voltage (as same pin out). The same appears with the midpoint, with the Blue line on RJ-45 being shorted to their 3.3V net, which powers everything else (assuming the buck regulator is bypassed). With regards to the MUX, it's all powered via a Qwiic connector, so the 3.3V net can easily be 5-volts as well. From this reasoning, does it seem like the Sparkfun boards can work with 3.3V and 5V I2C logic depending on what logic level your MCU runs at?