Interfacing Arduino with I2C LCD

Generally to be able to use an LCD display we need at least 6 free pins, but the number of pins can be minimized with the help of external components like PCF8574 (or PCF8574A) I2C I/O expander, that’s allows us to use only 2 pins from our microcontroller. This small post shows how to connect the Arduino with I2C LCD provided with PCF8574 I/O expander.

Hardware Required:

  • Arduino board
  • LCD screen (16×2, 20×4 …)
  • PCF8574 I/O expander (or PCF8574A)   —   PCF8574 datasheet
  • 5 x 10k ohm resistor
  • 330 ohm resistor
  • 10k ohm variable resistor or potentiometer
  • Breadboard
  • Jumper wires

Arduino with I2C LCD - PCF8574 I/O expander

Interfacing Arduino with I2C LCD circuit:
Example circuit diagram is shown in the image below.

Arduino I2C LCD PCF8574 circuit

(All grounded terminals are connected together)

The main component of the I2C LCD display is the PCF8574 I/O expander, with only two pins SDA and SCL we get a maximum of 8 pins from P0 to P7. PCF8574A also can be used but it has a different address.

All LCD data pins are connected to the PCF8574 where: RS, RW, E, D4, D5, D6 and D7 are connected to P0, P1, P2, P4, P5, P6 and P7 respectively.

PCF8574 I/O expander SDA and SCL pins are connected to Arduino pin A4 and A5 respectively (Arduino SDA and SCL pins).

PCF8574 I/O expander A0, A1 and A2 pins are the address pins which decide the I2C address of the chip. In this example each pin is connected to +5V through a 10k ohm resistor (the 10k resistor is optional, each pin can be connected directly to +5V).

The I2C address of the PCF8574 is: 0x20 | A2 A1 A0 ( | means OR)
In our circuit A2, A1 and A0 are connected to +5V (through 10k resistors) which means the I2C address is equal to 0x20 | 7 = 0x27

If the PCF8574A is used instead of the PCF8574 the I2C address is: 0x38 | 7 = 0x3F.

Interfacing Arduino with I2C LCD code:
In this interfacing I used a small library named LiquidCrystal_I2C (LiquidCrystal_I2C.h), this library simplifies the Arduino code, it can be downloaded from the links below. After downloading the library, unzip the folder and add it to Arduino libraries folder (for example: C:\Program Files\Arduino\libraries):
LiquidCrystal_I2C  —  direct link

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