Solder this interface module onto the back of your 16×2 or 20×4 LCD module with the standard HD44780 parallel interface to enable I2C communications with your display. What used to take six I/O pins, a contrast pot, and a backlight resistor now only requires Power (+5V), Ground, SDA and SCL.
Use with this library: https://github.com/marcoschwartz/LiquidCrystal_I2C
(Use the Arduino Library Manager to install it.)
There are three solder jumpers available to set the I2C address to one of 8 options. If the IC part number is PCF8574AT, the base address is 0x3F. For PCF8574T, the base address is 0x27.