How to Use PCF8575C: Examples, Pinouts, and Specs

The PCF8575C is a 16-bit I/O port expander that communicates via the I2C protocol. It enables microcontrollers to control up to 16 digital input/output pins using only two communication lines (SCL and SDA). This makes it an excellent choice for applications where additional GPIO pins are required but limited by the microcontroller's onboard resources.

• Expanding GPIO pins for microcontrollers like Arduino, Raspberry Pi, or ESP32
• Controlling LEDs, relays, or other digital devices
• Reading multiple button or switch inputs
• Home automation systems
• Industrial control systems

• Operating Voltage: 2.5V to 5.5V
• I2C Address Range: 0x20 to 0x27 (configurable via address pins A0, A1, A2)
• Maximum I2C Clock Frequency: 400 kHz (Fast Mode)
• Number of I/O Pins: 16 (P0.0 to P0.7 and P1.0 to P1.7)
• Output Current: 25 mA (sink) per pin
• Input Current: ±1 µA
• Operating Temperature Range: -40°C to +85°C
• Package Types: TSSOP, SOIC

The PCF8575C has 24 pins. Below is the pin configuration:

1. Power Supply: Connect the VCC pin to a 3.3V or 5V power source and the GND pin to ground.
2. I2C Communication: Connect the SCL and SDA pins to the corresponding I2C pins on your microcontroller. Use pull-up resistors (typically 4.7kΩ) on both lines.
3. Address Configuration: Set the I2C address by connecting the A0, A1, and A2 pins to either VCC (logic high) or GND (logic low).
4. I/O Pins: Use the P0.x and P1.x pins as digital inputs or outputs. Configure them by sending the appropriate data via I2C.
5. Interrupt Pin: Optionally, connect the INT pin to your microcontroller to detect changes in input states.

• Ensure the total current drawn by the I/O pins does not exceed the device's maximum ratings.
• Use decoupling capacitors (e.g., 0.1 µF) near the VCC pin to stabilize the power supply.
• Avoid leaving unused input pins floating; connect them to GND or VCC as needed.
• When using the PCF8575C with a 5V system, ensure the microcontroller's I2C pins are 5V-tolerant or use level shifters for compatibility.

Below is an example of how to use the PCF8575C with an Arduino UNO to toggle an LED connected to one of its pins:

#include <Wire.h> // Include the Wire library for I2C communication

#define PCF8575C_ADDRESS 0x20 // Default I2C address of the PCF8575C

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

  // Set all pins to output and turn them off
  Wire.beginTransmission(PCF8575C_ADDRESS);
  Wire.write(0x00); // Low byte (P0.0 to P0.7)
  Wire.write(0x00); // High byte (P1.0 to P1.7)
  Wire.endTransmission();
}

void loop() {
  // Turn on an LED connected to P0.0
  Wire.beginTransmission(PCF8575C_ADDRESS);
  Wire.write(0x01); // Set P0.0 high, others low
  Wire.write(0x00); // Keep P1.x pins low
  Wire.endTransmission();
  delay(1000); // Wait for 1 second

  // Turn off the LED
  Wire.beginTransmission(PCF8575C_ADDRESS);
  Wire.write(0x00); // Set all P0.x pins low
  Wire.write(0x00); // Keep P1.x pins low
  Wire.endTransmission();
  delay(1000); // Wait for 1 second
}

1. I2C Communication Not Working

   • Ensure the SCL and SDA lines have proper pull-up resistors (4.7kΩ recommended).
   • Verify the I2C address matches the configuration of the A0, A1, and A2 pins.
   • Check for loose or incorrect wiring.

2. I/O Pins Not Responding

   • Confirm the PCF8575C is powered correctly (check VCC and GND connections).
   • Ensure the I/O pins are configured properly in your code.
   • Check if the total current drawn by the I/O pins exceeds the device's limits.

3. Interrupt Pin Not Functioning

   • Verify that the INT pin is connected to the correct microcontroller pin.
   • Ensure the interrupt functionality is enabled in your code.

• Can the PCF8575C handle analog signals? No, the PCF8575C is designed for digital input/output only.

• What happens if multiple PCF8575C devices share the same I2C address? Address conflicts will occur, leading to communication errors. Use unique addresses for each device by configuring the A0, A1, and A2 pins.

• Is the PCF8575C compatible with 3.3V systems? Yes, the PCF8575C operates within a voltage range of 2.5V to 5.5V, making it compatible with both 3.3V and 5V systems.