[41south]

The other thing to look out for if directly connecting a sensor to the bus extension will be the pullup resistors. The TX board already has those and in my experience most breakout type modules also have them - so they end up in parallel. It appears that best practice is to have a set of pull-ups in each section of the bus, therefore reinforcing the need for a second bus extension chip at the sensor end of the extended I2C bus.

In fact taking another look at the circuit, if I am correct, no sensors should have the pull-ups fitted when the resistors R7 and R8 are fitted. The Adafruit SHT31-D module for instance has 10k resistors on board, which will end up in parallel with R7 and R8