I wasted 2 days with a problem with an I2C expander (PCF8574) and a Nodemcu Esp8266. I wanted to read some push buttons using the interrupt from the PCF8574, but it didn’t work…
Read the datasheet, read from forums, searching on google… but the thing didn’t work. The INT pin, sometimes, was locked and the I2C bus didn’t work.
I put EVERY resistors suggested from the datasheet and nothing happens…
Suddenly, I discover a bug on the code (my fault) (a problem reading from PCF8574 in order to avoid bounces from the push button) and all start to work properly.
…then I removed, one by one, the resitors (SDA, SCL, INT) and still it works.
…then I removed all the pull-up resistors from the push-buttons and still it works.
Then my question is: ¿Is really necessary all those resistors?