Backlight brightness does not work as expected

[wellu]

Seems that void LiquidCrystal_PCF8574::setBacklight(uint8_t brightness) does not work as expected and at least on my display it is merely on or off. Passing 0 toggless the backlight off and any positive value toggless it fully on.

Might be that it works on some other boards though.

[ascodeasice]

My arduino uno/ nano also can only turn the light on and off