Summary
I understand now why Adafruit use 10k resistors on all their stuff
Because so many of their boards have their own pull ups or level shifters or whatever
Let's say you connect two I2C buses with 10k's on each side together
In parallel you end up at 5K which is really close to the recommended 4.7k
But because we switched everything to 4.7k
When two sides get connected now you end up at 2.35k which is dangerously close to the minimum allowable for I2C
Actually some of the stuff might not even work at all because it will end up being too strong of a pullup
So yeah, rough
I added a buffer in front of the TCA on the Flight Controller Board TCA I2C Multiplexer
Basically worst case, I think we would be looking at 4.7k / 3 which is 1.57k
When the RP2350 is connecting all the way through to a sensor on a solar face I think the combined pull ups on the I2C bus will be too strong to allow it to operate correctly
I need to test this experimentally
Possible Remedy
But I think the easiest thing for us to do to remedy this will be to yeet the TCA I2C buffer on the FC board
Summary
I understand now why Adafruit use 10k resistors on all their stuff
Because so many of their boards have their own pull ups or level shifters or whatever
Let's say you connect two I2C buses with 10k's on each side together
In parallel you end up at 5K which is really close to the recommended 4.7k
But because we switched everything to 4.7k
When two sides get connected now you end up at 2.35k which is dangerously close to the minimum allowable for I2C
Actually some of the stuff might not even work at all because it will end up being too strong of a pullup
So yeah, rough
I added a buffer in front of the TCA on the Flight Controller Board TCA I2C Multiplexer
Basically worst case, I think we would be looking at 4.7k / 3 which is 1.57k
When the RP2350 is connecting all the way through to a sensor on a solar face I think the combined pull ups on the I2C bus will be too strong to allow it to operate correctly
I need to test this experimentally
Possible Remedy
But I think the easiest thing for us to do to remedy this will be to yeet the TCA I2C buffer on the FC board