Arduino PCF8574: Add 8 GPIO Pins Over I2C | ShillehTek

May 15, 2026 33 views

Project

Build an Arduino PCF8574 I2C GPIO expander project to drive 8 LEDs using only SDA and SCL, freeing pins for bigger builds with ShillehTek.

15 min Beginner3 parts

Project Overview

Arduino + PCF8574 I2C expander: This project shows how to use a PCF8574 I2C GPIO expander with an Arduino (UNO, Nano, or Pro Mini) to add 8 extra digital I/O pins over just two wires (SDA and SCL) and drive 8 LEDs.

You can stack up to 8 PCF8574 boards on one I2C bus for 64 extra pins total. The PCF8574 is also the common "backpack" chip used on many LCD1602 + I2C modules.

Time: ~15 minutes
Skill level: Beginner
What you will build: An Arduino driving 8 LEDs through a PCF8574 using only two Arduino pins.

PCF8574 I2C GPIO expander module used to add 8 digital pins to an Arduino — The PCF8574 provides 8 GPIO pins over I2C with an address you can select.

Parts List

From ShillehTek

PCF8574 I²C Serial Interface Adapter - the 8-bit I2C GPIO expander module used in this build
Arduino Nano V3.0 Pre-Soldered - example Arduino board to control the PCF8574 over I2C
120 PCS Dupont Jumper Wires - for quick breadboard wiring

External

8 LEDs + 8x 220 ohm current-limiting resistors
Breadboard

Note: The PCF8574 default I2C address is 0x20 with A0/A1/A2 tied LOW. Pull them HIGH in different combinations for 0x21, 0x22, up to 0x27 (8 boards on one bus).

Step-by-Step Guide

Step 1 - Inspect the Module

Goal: Identify the PCF8574 pins you will wire to the Arduino and the LED outputs.

What to do: Locate the power and I2C pins (VCC, GND, SDA, SCL), the 8 GPIO pins (P0 to P7), and the address select jumpers (A0, A1, A2).

Front of PCF8574 I2C expander module showing VCC GND SDA SCL and P0 to P7 pins — Eight output pins (P0 to P7), four power and signal pins (VCC, GND, SDA, SCL), and three address jumpers (A0, A1, A2).

Back of PCF8574 I2C expander module showing bypass capacitor and pull-up resistors — Back side components such as the bypass capacitor and pull-up resistors.

Expected result: You know which pins connect to Arduino I2C and which pins will drive the LEDs.

Step 2 - Wire It Up

Goal: Connect the PCF8574 to the Arduino over I2C and wire 8 LEDs to the expander outputs.

What to do: Make the I2C and power connections first, then connect each PCF8574 output pin (P0 to P7) to an LED and resistor.

Arduino wired to a PCF8574 I2C expander on a breadboard with 8 LEDs connected to P0 to P7 — Two I2C wires from the Arduino, plus 8 LEDs and resistors connected to P0 to P7.

VCC to 5V, GND to GND
SDA to A4, SCL to A5
P0 to P7 to LED anode to 220 ohm to GND

Expected result: The Arduino and PCF8574 share power and ground, I2C is connected (SDA and SCL), and each output pin can control one LED through a resistor.

Step 3 - Upload the Sketch

Goal: Send one byte over I2C to control the 8 PCF8574 pins.

What to do: Copy the sketch below into the Arduino IDE and upload it to your board. It uses I2C address 0x20, which matches the default A0/A1/A2 jumper state (all LOW).

Code:

#include <Wire.h>

const byte ADDR = 0x20;

void writeAll(byte b) {
  Wire.beginTransmission(ADDR);
  Wire.write(b);
  Wire.endTransmission();
}

void setup() {
  Wire.begin();
  Serial.begin(9600);
}

void loop() {
  for (byte i = 0; i < 8; i++) {       // Walk one lit LED through the bank
    writeAll(1 << i);
    delay(150);
  }
  writeAll(0xFF);                         // All on
  delay(500);
  writeAll(0x00);                         // All off
  delay(500);
}

One byte written over I2C controls 8 pins. The bit at position N maps to P(N).

Expected result: The Arduino uploads successfully and begins writing patterns to the PCF8574 over I2C.

Step 4 - Watch the LEDs

Goal: Confirm the PCF8574 is driving all 8 outputs through a simple chase and all-on/all-off pattern.

What to do: Power the circuit and observe the LED sequence.

Eight LEDs blinking in a chase pattern driven by an Arduino through a PCF8574 I2C expander — One LED chases across the bank, then transitions to full on and full off.

PCF8574 I2C expander driving multiple LEDs at once while using only two Arduino I2C pins — All 8 LEDs are controlled without consuming additional Arduino GPIO.

Expected result: A single LED walks across P0 to P7, then all LEDs turn on, then all turn off, repeating.

Step 5 - Where to Take It Next

Goal: Understand common ways to extend this PCF8574 setup for larger I/O projects.

What to do: Consider these next steps as you expand your design.

Read 8 buttons in parallel by configuring pins as inputs with internal pull-ups
Stack 4 PCF8574s for 32 GPIO over the same 2-wire bus
Drive a 4x4 keypad without consuming any native GPIO
Use a PCF8574-backed LCD1602 backpack instead of wiring 12 lines

Expected result: You have a clear path for scaling from 8 extra pins to larger I2C-based I/O systems.

Conclusion

The Arduino plus PCF8574 is a simple way to stop running out of pins: two I2C wires give you eight new GPIO lines, and you can expand further by changing the I2C address and adding more modules.

Want the exact parts used in this build? Grab them from ShillehTek.com. If you want help customizing this project or building something for your product, check out our IoT consulting services.

Credits: Photos and example code referenced from Instructables.