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 is designed to provide additional GPIO (General Purpose Input/Output) pins for microcontrollers, making it an ideal solution for applications requiring more I/O capabilities than the microcontroller natively supports. The device operates as a bidirectional I/O expander, allowing each pin to be configured as either an input or an output.

• Expanding GPIO pins for microcontrollers in embedded systems
• Driving LEDs, relays, or other output devices
• Reading multiple switches or sensors
• Home automation systems
• Industrial control systems
• Robotics and IoT projects

• Operating Voltage: 2.5V to 5.5V
• I2C Address Range: Configurable via A0, A1, and A2 pins (up to 8 devices on the same bus)
• 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 (typical)
• Operating Temperature Range: -40°C to +85°C
• Package Options: TSSOP, SOIC, and others

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

1. Power Supply: Connect the VCC pin to a 2.5V–5.5V 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 4.7 kΩ) on both lines.
3. Address Configuration: Set the I2C address by connecting A0, A1, and A2 to either VCC or GND. This allows up to 8 devices to share the same I2C bus.
4. GPIO Pins: Use the P0.x and P1.x pins as inputs or outputs. Configure them by sending the appropriate data via I2C.
5. Interrupt Pin: The INT pin can be used to detect changes in input states. It is active low and requires external pull-up if used.

• Ensure the I2C bus voltage matches the operating voltage of the PCF8575C.
• Avoid exceeding the maximum current ratings for the GPIO pins to prevent damage.
• Use decoupling capacitors (e.g., 0.1 µF) near the VCC pin for noise suppression.
• If using the INT pin, ensure it is properly configured in your microcontroller's interrupt system.

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

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

#define PCF8575C_ADDRESS 0x20 // Default I2C address (A0, A1, A2 = GND)

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

  // Set all pins as outputs 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); // Set all P1.x pins low
  Wire.endTransmission();
  delay(1000); // Wait for 1 second
}

1. No Response from the Device:

   • Ensure the I2C address is correctly configured and matches the address in your code.
   • Check the pull-up resistors on the SDA and SCL lines.
   • Verify the power supply voltage is within the specified range.

2. GPIO Pins Not Responding:

   • Confirm the pins are correctly configured as inputs or outputs.
   • Check for shorts or excessive current draw on the GPIO pins.

3. Interrupt Pin Not Working:

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

• Use an I2C scanner sketch to verify the PCF8575C is detected on the bus.
• Check all connections and solder joints for continuity.
• Use a logic analyzer or oscilloscope to monitor I2C communication if issues persist.