Cascadable I2C to GPIO Expander 8-64 Ports with PCF8574

Overview

The I2C to GPIO Expander is an 8-bit parallel input/output interface module based on the PCF8574 I2C port expander. This module allows microcontrollers and embedded systems to increase the number of general-purpose I/O lines available using a standard I2C bus interface. The device supports both input and output modes on each of the eight I/O pins and facilitates digital control, status monitoring, and external peripheral interfacing without consuming additional microcontroller pins.

The module integrates onboard 10 kΩ pull-up resistors on each I/O line and includes configurable I2C address selection options. Five address selection pads allow the I2C bus address to be modified by cutting or configuring trace options, enabling multiple devices to be used on the same bus.

In systems where multiple I2C to GPIO Expander modules are cascaded, some pull-up resistors may need to be removed to prevent excessive loading of the I2C bus.

Key Features

• I2C to GPIO Expander using PCF8574 or equivalent I2C port expander IC
• 8 general-purpose bidirectional I/O pins
• Supports both input and output operation on each pin
• Onboard 10 kΩ pull-up resistors on all I/O lines
• Configurable I2C address selection via trace pads
• Compatible with standard I2C master devices operating at 3.3 V or 5 V
• Cascadable I2C devices with address modification
• Suitable for microcontrollers, development boards, and embedded systems

Electrical and Usage Notes

• The module requires a stable I2C clock and data bus from a host controller
• I2C address selection pads must be configured (cut, solder, or bridge) to avoid address conflicts on the bus
• Onboard pull-up resistors provide default line biasing; however, excessive parallel pull-ups from multiple modules may increase I2C load and reduce signal integrity
• For cascaded configurations with multiple modules, selectively removing some pull-up resistors may be necessary to maintain proper bus timing and signal quality
• Logic levels and supply voltage must match the host I2C master (typically 3.3 V or 5 V systems)
• Ensure proper decoupling and supply bypass to minimize noise on I2C and GPIO lines

Typical Applications

• Expanding microcontroller I/O for sensors, switches, and indicators
• Keypad and pushbutton interfacing
• LED array control and status monitoring
• Relay and actuator control in embedded systems
• Low-speed digital expansion for I2C-based applications
• Prototype and educational hardware development

Specifications