How to Use PCF8575 IO Expander Module I2C 16 PIN: Examples, Pinouts, and Specs

The PCF8575 IO Expander Module is a 16-bit I2C-bus and SMBus I/O expander designed to effectively expand the number of digital input/output (I/O) pins available in a microcontroller or microprocessor-based system. This component is particularly useful in applications where additional I/O pins are needed for buttons, LEDs, or other digital signals, and is commonly used in conjunction with platforms like Arduino, Raspberry Pi, and other microcontroller boards.

• Expanding I/O capabilities in microcontroller projects
• Interfacing with a large number of sensors or actuators
• Building keypad interfaces for user input
• Home automation systems
• Industrial control systems

• Operating Voltage: 2.5V to 5.5V
• I2C Bus Speed: Up to 400 kHz (Fast-mode)
• I/O Pins: 16-bit remote I/O pins for the I2C bus
• Interrupt Output: Active LOW interrupt output
• Addressing: 8 hardware address pins for 64 possible addresses

1. Powering the Module: Connect VDD to a 2.5V to 5.5V power supply and VSS to ground.
2. Setting the Address: Connect A0, A1, and A2 to either VDD or VSS to set the hardware address.
3. Connecting to a Microcontroller:
   • Connect SDA and SCL to the corresponding I2C data and clock lines on your microcontroller.
   • Optionally, connect the INT pin to an interrupt-capable pin on your microcontroller to use the interrupt feature.

• Ensure pull-up resistors are connected to the SDA and SCL lines, as they are required for proper I2C communication.
• Avoid setting the same address for multiple devices on the same I2C bus.
• When using the interrupt feature, configure the microcontroller's interrupt settings appropriately.

#include <Wire.h>

// PCF8575 I2C address (adjust based on A0-A2 connections)
const int expanderAddress = 0x20;

void setup() {
  Wire.begin(); // Initialize I2C
  Serial.begin(9600); // Start serial communication for debugging

  // Set all pins of PCF8575 to output
  Wire.beginTransmission(expanderAddress);
  Wire.write(0x00); // Low byte
  Wire.write(0x00); // High byte
  Wire.endTransmission();
}

void loop() {
  // Toggle all pins
  Wire.beginTransmission(expanderAddress);
  Wire.write(0xFF); // Low byte
  Wire.write(0xFF); // High byte
  Wire.endTransmission();
  delay(1000);

  Wire.beginTransmission(expanderAddress);
  Wire.write(0x00); // Low byte
  Wire.write(0x00); // High byte
  Wire.endTransmission();
  delay(1000);
}

• I2C Communication Failure: Check the wiring, ensure pull-up resistors are installed, and verify that no two devices have the same address.
• No Response from I/O Pins: Make sure the PCF8575 is properly powered and that the I2C address is correctly set according to the A0-A2 pins.

• Use an I2C scanner sketch to confirm the PCF8575 is detected on the bus.
• Check for soldering issues or loose connections that might affect signal integrity.
• If using the interrupt feature, ensure the INT pin is correctly configured in your microcontroller's firmware.

Q: Can I use the PCF8575 with a 3.3V system? A: Yes, the PCF8575 operates from 2.5V to 5.5V, making it suitable for both 3.3V and 5V systems.

Q: How many PCF8575 expanders can I connect to a single I2C bus? A: You can connect up to 64 devices, provided that each has a unique hardware address set by the A0-A2 pins.

Q: What is the maximum current each I/O pin can sink or source? A: The PCF8575 I/O pins are not designed to drive high currents. Refer to the datasheet for exact current specifications, and use external transistors or drivers if higher currents are needed.