Overview

The PCA8574 is an 8-bit I/O expander that provides general-purpose remote I/O expansion via the I2C bus. It’s functionally compatible with the PCF8574 and shares the same component platform in ESPHome.

The module features:

• 8 quasi-bidirectional I/O ports
• I2C interface (up to 100kHz)
• Low standby current consumption
• Open-drain interrupt output
• Addresses: 0x20-0x27 (PCA8574) or 0x38-0x3F (PCA8574A)
• Operating voltage: 2.5V-6V
• 5V tolerant I/Os
• Latched outputs with high current drive
• Active LOW interrupt pin

Configuration Notes

• Requires I2C interface
• Platform: pcf8574 (ESPHome uses PCF8574 platform for PCA8574)
• Default I2C addresses: 0x20-0x27 (PCA8574) or 0x38-0x3F (PCA8574A)
• Default address in ESPHome: 0x21
• Each pin can be configured as input or output
• Pins can be used with binary_sensor, switch, and other GPIO-based components
• Provides 8 additional GPIO pins over I2C
• Pin numbers: 0-7

Example Configuration

# I2C bus configuration
i2c:
  sda: GPIO21
  scl: GPIO22
  scan: true

# PCA8574 configuration
pcf8574:
  - id: 'pca8574_hub'
    address: 0x20  # or 0x38 for PCA8574A
    pcf8575: false

# Individual outputs
switch:
  - platform: gpio
    name: "PCA8574 Pin #0"
    pin:
      pcf8574: pca8574_hub
      number: 0
      mode:
        output: true
      inverted: false

# Individual inputs
binary_sensor:
  - platform: gpio
    name: "PCA8574 Pin #7"
    pin:
      pcf8574: pca8574_hub
      number: 7
      mode:
        input: true
      inverted: false

Hardware Notes

• The PCA8574 and PCA8574A differ only in their I2C address ranges
• All pins are quasi-bidirectional (can be used as input or output without reconfiguration)
• Internal weak pull-up resistors on all I/O pins
• Maximum output sink current: 25mA per pin
• Address pins A0, A1, A2 configure the I2C address
• INT pin can be connected to an MCU interrupt pin to detect input changes