PCF8574 I/O Expander

Operating Voltage

2.5 V

Operating Voltage

6 V

Logic Level

0.7 x VCC V

Logic Level

0.3 x VCC V

Interface

I2C

Standby Current Consumption

10 μA

Operating Current

40 μA

I2c Clock Frequency

100 kHz

Temperature Range

-40 °C

Temperature Range

85 °C

Package

TVSOP, SOIC, PDIP, TSSOP, VQFN

Operates from 2.5-6 V (per the datasheet specs) on I2C, with logic thresholds referenced to VCC, so it suits both 3.3 V and 5 V buses.

• Adding 8 I/O pins over I2C (the common LCD 'backpack')
• Reading buttons / driving LEDs from few pins
• Bus expansion with up to 8 chips per bus

• Outputs are quasi-bidirectional (weak high) — fine for LEDs/inputs, not strong sourcing.
• Set the A0-A2 address pins; up to 8 devices per bus.
• The INT pin flags input changes — wire it to a GPIO to avoid polling.

• ESP32 DevKitC (WROOM-32)Espressif · ESP32-WROOM-32
• Raspberry Pi PicoRaspberry Pi · RP2040
• SSD1306 OLED DriverSSD1306 · Solomon Systech

Community starter examples — minimal, unofficial, and provided to get you wiring fast. Verify against the manufacturer datasheet before relying on them.

// PCF8574 8-bit I2C I/O expander — community starter example
// No library needed: write one byte = the 8 output pins (P0..P7).
#include <Wire.h>

const byte ADDR = 0x20;   // A2..A0 = 000; PCF8574A base is 0x38

void writePort(byte value) {
  Wire.beginTransmission(ADDR);
  Wire.write(value);
  Wire.endTransmission();
}

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

void loop() {
  writePort(0xFF);   // all P0..P7 HIGH
  delay(500);
  writePort(0x00);   // all LOW
  delay(500);
}

# PCF8574 I2C I/O expander (ESP32) — community starter example
# No driver needed: one byte = the 8 pins
from machine import Pin, I2C
import time

i2c = I2C(0, scl=Pin(22), sda=Pin(21))
ADDR = 0x20

while True:
    i2c.writeto(ADDR, b"\xFF")   # all HIGH
    time.sleep(0.5)
    i2c.writeto(ADDR, b"\x00")   # all LOW
    time.sleep(0.5)