This is my 1st post and I'll try my best to describe the problem.
I've been doing this little project with Arduino Uno, DHT22 sensor and 20x4 display.
A Co-worker has given me I2c module that they have made with pcf8574 chip on it (It isn't used with Arduino, but for debugging and wrote the code in C for the display). And after weeks of unsuccessful attempts to make it work...i figured that the pins are wired differently, I've found a thread where someone had a similliar problem. https://forum.arduino.cc/index.php?topic=523214.0
Basically the pin wiring on pcf8574 is different than what it's supposed to be. Can the library be adjusted and defined differently?
I'm aware that the module is so cheap i could just order a new one that works out of the box, but if there's a way around this one i would be glad to try and ''fix it''.
The display is working, and the I2c module works if its used with the code it was written for on a different application.
EDIT: I've managed to do solve the problem. I've found the constructor in the code.
hd44780_I2Cexp lcd(addr, chiptype, rs,[rw],en,d4,d5,d6,d7,bl,blpol);
hd44780_I2Cexp lcd(0x27, I2Cexp_PCF8574, 0,1,2,4,5,6,7,3,HIGH); // with rw support
And managed to edit and change so the pinout is correct. The display is working now.