Expansion Port Cascadable Module PCF8574 I/O I2C Red

Features

• Support cascading: You can use up to 8 PCF8574 modules to extend up to 64 digital I/O ports at the same time. This makes it possible to interface with a large number of sensors and devices using just a few microcontroller pins.
• Address configuration: The PCF8574 can be configured with a toggle switch to change its I2C address. This allows you to use multiple PCF8574 modules on the same I2C bus without addressing conflicts.
• Compact size: The PCB size of the PCF8574 is small, measuring just 36 x 16mm (1.41 x 0.62 inches). This makes it easy to integrate into your electronic projects.
• Output testing: The PCF8574 includes a testing feature that automatically toggles the P0-P7 ports every 2 seconds, outputting a high level and then a low level. If you set the three toggle switches to the ON position, the I2C address of the module will be set to 0x27.
• Voltage range: The PCF8574 is designed to operate with a voltage range of 2.5 to 6 volts, making it compatible with a wide range of microcontrollers and electronic devices.

Principle of Work

The PCF8574 module is an I/O expander that works by communicating with a microcontroller through the I2C protocol. The I2C protocol is a two-wire serial communication protocol that allows multiple devices to be connected to the same bus. The PCF8574 uses this protocol to communicate with the microcontroller and expand its digital I/O capabilities. The PCF8574 module has 8 I/O ports, labeled as P0 to P7, which can be used as either inputs or outputs. Each I/O port can be individually configured as an input or an output by writing to the corresponding bit in the PCF8574's control register. The PCF8574 also includes a latched output with high-current drive capabilities. This output is located on the device's 8-bit quasi-bidirectional I/O port (P0-P7), which can be used to directly drive LEDs or other small loads. One of the great features of the PCF8574 module is that it can be cascaded with other PCF8574 modules to expand the number of I/O ports. Each PCF8574 module has a unique I2C address, which can be set by a toggle switch on the module. By setting the I2C address of each module differently, you can connect up to 8 modules to the same I2C bus and control up to 64 digital I/O ports.

Multiple Addresses

If you daisy-chain the modules, you will need to set a different address for each of the modules.

Pinout of the Module

Pin 1: GND- Ground
Pin 2: VCC - Power supply voltage (2.5V to 6V)
Pin 3: SDA - Serial data input/output pin for I2C communication
Pin 4: SCL - Serial clock input pin for I2C communication
Pin 5-12: P0 to P7 - Bidirectional I/O ports that can be individually configured as inputs or outputs
Pin 13: A0 - Address bit 0, used to set the I2C address of the module
Pin 14: A1 - Address bit 1, used to set the I2C address of the module
Pin 15: A2 - Address bit 2, used to set the I2C address of the module

Applications

• Driving LEDs and other small loads: The latched output with high-current drive capabilities of the PCF8574 module makes it ideal for driving LEDs and other small loads.
• Input/output expansion for microcontrollers: The PCF8574 module provides a simple and cost-effective way to expand the number of digital I/O ports available to a microcontroller.
• Sensor interfacing: The PCF8574 module can be used to interface with a variety of sensors that require digital I/O ports for communication.
• Home automation: The PCF8574 module can be used in home automation projects to control lights, appliances, and other devices.
• Robotics: The PCF8574 module can be used in robotics projects to control motors, servos, and other devices that require digital I/O control.
• Industrial automation: The PCF8574 module can be used in industrial automation projects to control sensors, actuators, and other devices.

Circuit

• Connect the VCC pin of the PCF8574 module to the 5V pin of the Arduino.
• Connect the GND pin of the PCF8574 module to the GND pin of the Arduino.
• Connect the SDA pin of the PCF8574 module to the SDA pin of the Arduino.
• Connect the SCL pin of the PCF8574 module to the SCL pin of the Arduino.
• Connect the LED one by one to the module outputs and the short legs to the GND.

Library

Install the PCF8574 library in the Arduino IDE:

1. Download the library from a trusted source such as the official Arduino Library Manager or the GitHub repository.
2. Open the Arduino IDE and navigate to the "Sketch" menu. Select "Include Library" and then "Add .ZIP Library".
3. Navigate to the downloaded PCF8574 library ZIP file and select it. The library should now be installed in the Arduino IDE.
4. To verify that the library is installed, navigate to the "Sketch" menu and select "Import Library". The PCF8574 library should now appear in the list of available libraries.

Code

This code is an example of how to use the PCF8574 library to control the I/O ports of a PCF8574 module connected to an Arduino using the I2C protocol.

#include "PCF8574.h"

PCF8574 pcf8574(0x27); // Initialize the PCF8574 module with the I2C address

void setup() {
  pinMode(13, OUTPUT); // Set the built-in LED pin as an output
}

void loop() {
  pcf8574.write(0xFF); // Write all HIGH to the I/O ports (P0-P7)
  digitalWrite(13, HIGH); // Turn on the built-in LED
  delay(1000); // Delay for 1 second
  
  pcf8574.write(0x00); // Write all LOW to the I/O ports (P0-P7)
  digitalWrite(13, LOW); // Turn off the built-in LED
  delay(1000); // Delay for 1 second
}

The code:

1. It initializes the PCF8574 module with the I2C address 0x27.
2. In the setup() function, it sets the built-in LED pin (pin 13) as an output.
3. In the loop() function, it writes all HIGH to the I/O ports (P0-P7) of the PCF8574 module using the write() function of the PCF8574 library.
4. It turns on the built-in LED by setting its pin to HIGH using the digitalWrite() function.
5. It delays for 1 second using the delay() function.
6. It writes all LOW to the I/O ports (P0-P7) of the PCF8574 module using the write() function of the PCF8574 library.
7. It turns off the built-in LED by setting its pin to LOW using the digitalWrite() function.
8. It delays for 1 second using the delay() function.

Technical Details

• Operating voltage: 2.5V to 6V DC
• Number of I/O ports: 8 (P0-P7)
• I2C address: configurable via DIP switches (0x20 to 0x27)
• Current rating: up to 100mA per I/O port
• Operating temperature: -40°C to +85°C
• Communication protocol: I2C (Two-Wire Interface)
• Support for cascading up to 8 modules to extend up to 64 I/O ports
• Dimensions: 36mm x 16mm x 4mm (L x W x H)

Resources

• Datasheet

Comparisons