PCF8574 I2C Interface 8-Bit I/O MCU Expansion Board for Arduino – GPIO Expander Module

The PCF8574 I2C Interface 8-Bit I/O MCU Expansion Board is an I2C-based GPIO expander designed to provide additional digital I/O capability without consuming a large number of microcontroller GPIO pins.

The PCF8574 contains eight quasi-bidirectional I/O ports. These ports can be used for reading digital inputs or controlling digital outputs such as LEDs and other suitable interface circuitry. The IC uses a two-wire I2C bus consisting of SDA and SCL.

The three address inputs A0, A1, and A2 allow the device address to be configured. For the PCF8574 address configuration used by this module, the available addresses are commonly 0x20 through 0x27, allowing multiple boards to share one I2C bus when unique addresses are selected.

Features

• PCF8574-based 8-bit digital I/O expansion
• Adds 8 digital I/O ports to a microcontroller
• Uses two-wire I2C communication
• Configurable I2C address from 0x20 to 0x27
• A0, A1, and A2 address-selection jumpers
• Supports multiple expansion modules on one I2C bus
• Active-low interrupt output
• Suitable for both input and output applications
• Supports 3.3V and 5V module operation as specified
• Compatible with Arduino, ESP32, STM32, Raspberry Pi and other platforms
• Useful for projects where available MCU GPIO pins are limited

Applications

• Arduino GPIO expansion
• ESP32 and STM32 I/O expansion
• Relay and switch control
• LED control
• Sensor input expansion
• LCD and display interfacing
• Keypad and button interfaces
• Home automation
• Industrial and embedded control
• Robotics projects
• DIY electronics and educational projects

How to Use

1. Connect the module's VCC and GND to a suitable power supply.
2. Connect SDA to the MCU's I2C SDA pin.
3. Connect SCL to the MCU's I2C SCL pin.
4. Select the required I2C address using the A0, A1, and A2 jumpers.
5. Install the appropriate PCF8574 library or implement the I2C commands in your software.
6. Configure the eight P0–P7 pins as required by the application.
7. If required, connect INT to a suitable MCU interrupt-capable input for input-change detection.

The PCF8574 uses quasi-bidirectional I/O ports rather than conventional independently configured push-pull GPIO. Its ports power up as inputs with weak internal pull-up current, so the application circuit should account for the characteristics of the PCF8574 I/O architecture.

Important Notes

• Verify the module's actual supply and logic levels before connecting it to a 3.3V-only microcontroller.
• The 0x20–0x27 address range applies to the PCF8574 addressing configuration; PCF8574A variants use a different fixed address range.
• Each module on the same I2C bus should have a unique address.
• The PCF8574 is intended for digital I/O expansion, not for directly driving high-current loads.
• Use a suitable transistor, MOSFET, relay driver, or dedicated driver circuit for motors, relays, lamps, and other higher-current loads.
• I2C wiring should be kept reasonably short and properly connected.
• Pull-up resistors are required on the I2C bus if they are not already provided by the controller or module.
• The interrupt output is active-low and open-drain, so appropriate pull-up circuitry is required.
• Product appearance, connector style, and component branding may vary depending on available stock.
• Warranty/Return: This item is non-returnable. If it arrives damaged or does not function properly, contact the seller for assistance. Record an opening/unboxing video before opening the package.

Package Includes

• 1 × PCF8574 I2C Interface 8-Bit I/O Expansion Board