A 16x2 character LCD is one of the most common displays in Arduino projects, and it can be wired up two very different ways depending on how many pins the rest of the project can spare.
The direct method
In 4-bit mode the display normally consumes six MCU signals: RS, E, and four data lines, plus power, ground, contrast, and backlight connections. It does not consume “12 Arduino pins,” but it still uses substantially more GPIO than an I2C backpack.
The I2C adapter method
The common backpack uses a PCF8574 I/O expander on the I2C bus; it is not a shift register. The microcontroller needs only SDA and SCL plus power, while many backpacks provide address jumpers and the bus requires suitable pull-up resistors.
Why the adapter is usually worth it
Beyond simplifying the wiring dramatically, the I2C approach frees up ten or more pins for everything else in the project. Because I2C devices each carry their own address, more than one I2C peripheral — including a second display — can share the exact same two-wire bus without interfering with each other.
Programming both approaches
The direct-wired version uses the standard LiquidCrystal library that ships with the Arduino IDE. The I2C version instead uses the LiquidCrystal_I2C library, which needs the module's I2C address (found with a quick scanner sketch if it's not printed on the board) but otherwise offers the same core functions — printing text, positioning the cursor, and clearing the screen — once it's initialized.
You can find 16x2 LCD displays and I2C adapter modules at Juthour Tech.
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