ChenXu 2. What voltage is needed for Bela I2C SDA and SCL inputs? Currently with 5V VCC and RTC 2.2k pull-ups, the logic level of SDA and SCL pins is around 3.6V. (I am a little confused here on if I need to use 2.2k pull-ups. If I don't use, the logic level can't reach 3.3V. While the instruction above is not recommended to use them.)
you should not have more than 3.3V on Bela inputs, or you may destroy the CPU. I am not familiar with this particular chip, so you may want to check its datasheet.
ChenXu 1. Do Bela I2C SDA and SCL pins connect to BBB P9_20 and P9_19 and use BBB's 1.8k pull-ups mentioned in the above instruction?
I2C-2 is actually enabled on P9_20(SDA), P9_19(SCL), however the instructions at the page suggest to use
i2cdetect -y -r 1
which is for the I2C-1 bus. This is available on the 4-pin white breakout connector on the Bela cape. If you want to use it on P9_20, P9_19, you should use
i2cdetect -y -r 2
which addresses bus I2C-2.