How to Use PCF8574 IO Expansion Board: Examples, Pinouts, and Specs

The PCF8574 IO Expansion Board is a versatile module that utilizes the PCF8574T I²C I/O expander chip to increase the number of digital input/output (I/O) pins available to a microcontroller, such as an Arduino or Raspberry Pi. This expansion is particularly useful when the number of built-in I/O pins is insufficient for a given project. The board operates over the I²C bus, allowing multiple devices to be connected to the same bus with only two wires, thus saving valuable pin resources.

• Expanding I/O capabilities for microcontrollers
• Home automation systems
• Robotics and control systems
• DIY electronics projects

• Operating Voltage: 2.5V to 6V
• I²C Bus Voltage: 5V tolerant
• Number of I/O Pins: 8
• Max Output Current per Pin: 25 mA
• Max Input Current per Pin: 100 mA
• Address Range: 0x20 to 0x27 (8 addresses selectable via jumpers)

1. Connect VDD to the power supply (2.5V to 6V) and VSS to ground.
2. Connect SDA and SCL to the I²C data and clock lines of the microcontroller.
3. Set the I²C address using the A0, A1, and A2 address pins.
4. Interface with the PCF8574 using the I²C protocol to read from or write to the I/O pins.

• Ensure that the power supply voltage does not exceed the maximum rating of 6V.
• Use pull-up resistors on the SDA and SCL lines if they are not already present on the microcontroller board.
• Avoid drawing more than 25 mA from any single I/O pin.
• When using multiple PCF8574 boards on the same I²C bus, ensure that each has a unique address.

#include <Wire.h>

// Define the I2C address for the PCF8574 board
#define PCF8574_ADDRESS 0x20

void setup() {
  Wire.begin(); // Initialize I2C protocol
  pinMode(PCF8574_ADDRESS, OUTPUT); // Set all pins of PCF8574 as output
}

void loop() {
  // Turn on all the outputs
  Wire.beginTransmission(PCF8574_ADDRESS);
  Wire.write(0xFF); // Write 0xFF to turn on all pins
  Wire.endTransmission();
  delay(1000);

  // Turn off all the outputs
  Wire.beginTransmission(PCF8574_ADDRESS);
  Wire.write(0x00); // Write 0x00 to turn off all pins
  Wire.endTransmission();
  delay(1000);
}

• I²C Communication Failure: Ensure that the SDA and SCL lines are connected properly and that pull-up resistors are in place.
• Incorrect Addressing: Verify that the address set by the A0-A2 pins matches the address used in the code.
• Insufficient Power Supply: Make sure that the power supply is within the specified range and capable of delivering sufficient current.

• Use an I²C scanner sketch to confirm the address of the PCF8574 board.
• Check for soldering issues or loose connections that might affect the I²C communication.
• If multiple PCF8574 boards are used, ensure that there are no address conflicts.

Q: Can I use this board with a 3.3V system? A: Yes, the PCF8574 is 5V tolerant on the I²C bus, but ensure that VDD is within the 2.5V to 6V range.

Q: How many PCF8574 boards can I connect to a single I²C bus? A: You can connect up to 8 PCF8574 boards to a single I²C bus by setting unique addresses using the A0-A2 pins.

Q: Can I use this board for analog signals? A: No, the PCF8574 provides digital I/O expansion only. It cannot be used for analog signals.