I have three I2C bus devices: 1) gas sensor (3V), 2) temperature and humidity sensor (3V), and 3) ESP32 (3.3V). They all connect to an I2C bus master: ATMEGA32U4. Using the typical application circuit provided in the datasheet, I used 2.2K resistors for both bus master and bus devices. My question is, do I only need to connect a resistor to the bus master once, and not for every bus device added?
The 3 V sensors can be on the same bus (you only need one pullup resistor for SCL and one pullup resistor for SDA for each bus), and the 5 V bus can also be shared. It looks like you only need two PCA9306s -- one to level translate the 3 V bus and another to level translate the 3.3 V bus.
Thank you! It didn't occur to me that you can combine same level SCL/SDA buses.