How to Use PCF8575 Remote16-BIT I2C AND SMBus I/O Expander: Examples, Pinouts, and Specs

The PCF8575 is a versatile 16-bit I/O expander that communicates via the I2C or SMBus protocol. It is designed to provide additional input/output (I/O) pins for microcontrollers, enabling the expansion of GPIO capabilities in a wide range of applications. Each of the 16 GPIO pins can be individually configured as either an input or an output, making the PCF8575 suitable for tasks such as interfacing with sensors, controlling LEDs, or managing relays.

• Expanding GPIO pins for microcontrollers like Arduino, Raspberry Pi, or ESP32
• Driving LEDs, relays, or other output devices
• Reading multiple switches or sensors
• Industrial automation and control systems
• Home automation projects

The following table outlines the key technical details of the PCF8575:

The PCF8575 has 24 pins, with the following configuration:

1. Power Supply: Connect the VDD pin to a 3.3V or 5V power source, and the VSS pin to ground.
2. I2C Communication: Connect the SDA and SCL pins to the corresponding I2C pins on your microcontroller. Use pull-up resistors (typically 4.7kΩ) on both SDA and SCL lines.
3. Address Configuration: Set the I2C address by connecting the A0, A1, and A2 pins to either VDD (logic high) or VSS (logic low). This allows up to 8 devices to share the same I2C bus.
4. GPIO Pins: Connect the GPIO pins (P0.0 to P1.7) to your desired input or output devices.

The following example demonstrates how to use the PCF8575 with an Arduino UNO to toggle an LED connected to one of the GPIO pins.

#include <Wire.h>
#include <PCF8575.h> // Include the PCF8575 library

PCF8575 expander(0x20); // Initialize the PCF8575 with I2C address 0x20

void setup() {
  Wire.begin(); // Initialize I2C communication
  expander.begin(); // Start the PCF8575
  expander.pinMode(P0, OUTPUT); // Set pin P0 as an output
}

void loop() {
  expander.digitalWrite(P0, HIGH); // Turn on the LED connected to P0
  delay(1000); // Wait for 1 second
  expander.digitalWrite(P0, LOW); // Turn off the LED
  delay(1000); // Wait for 1 second
}

• Use pull-up resistors on the SDA and SCL lines to ensure reliable I2C communication.
• Avoid exceeding the maximum current ratings for the GPIO pins to prevent damage.
• Use decoupling capacitors (e.g., 0.1µF) near the VDD pin to stabilize the power supply.

1. Device Not Responding on I2C Bus

   • Cause: Incorrect I2C address or wiring.
   • Solution: Verify the address configuration (A0, A1, A2 pins) and check the connections for SDA and SCL.

2. GPIO Pins Not Functioning as Expected

   • Cause: Incorrect pin mode configuration.
   • Solution: Ensure that each pin is properly configured as an input or output using the appropriate library functions.

3. Interrupt Pin Not Triggering

   • Cause: Interrupts not enabled or misconfigured.
   • Solution: Check the datasheet for interrupt configuration details and ensure the INT pin is connected to the microcontroller.

Q: Can the PCF8575 handle 5V logic levels?
A: Yes, the PCF8575 supports operating voltages from 2.5V to 5.5V, making it compatible with both 3.3V and 5V systems.

Q: How many PCF8575 devices can I connect to a single I2C bus?
A: Up to 8 devices can be connected by configuring the A0, A1, and A2 address pins.

Q: Can I use the PCF8575 for PWM output?
A: The PCF8575 does not natively support PWM. However, you can simulate PWM by toggling the GPIO pins in software.

Q: What is the maximum I2C clock speed supported?
A: The PCF8575 supports I2C clock speeds up to 400kHz (Fast Mode).