I'm using PCF8574 since more than 10 years to sense dry contacts (PCF is used in input mode). The contacts are located between 1 and 4 meters away form the board, and its action just consist to pull the input (P0-P7) to Vss. The environment is not a a lab but it is not too much "noisy".
This has been working very well so far until last months where I start to got strange behaviors:
As long a s the contact is very close to the PCF8574 (and cable length is short < 0.2m), its still working as designed.
If the cable length increase, at some stage (not always the same distance) the PCF8574 suddenly "collapse" Vcc, like if there is a shortcut inside (and the chips gets very hot).
Trying to understand, I did several experiments and conclude that the problem concerns a specific lot number:
I do not know if and where I can retrieve data from this batch...
Can someone help