I got some TI PCF8575 I²C I/O expander devices some years ago and never gave them a try. Yesterday I did... In the title they are named PF575, this is because this is what is printed on the device.

I wrote code for making a LED blink using the I/O expander as simple as possible.

Here you see my setup on a breadboard. On the left is the LED connected via a PNP transistor for voltage control.

pcf8575 arduino breadboard

I only had 24-SSOP packages so I needed to solder the PCF8575 to a DIP adapter for making it breadboard friendly.

pcf8575

My code:

#include <Wire.h>

/** 
 *  Arduino PF575/PCF8575 I2C I/O port exapander LED blink example
 *  
 *  Setup:
 *  
 *  1. Connect A0, A1 and A2 to GND to set the address to 0x20.
 *  2. Connect SDL and SCL to the Arduino's I2C bus.
 *  3. Connect a LED to the P0 port of the I2C exapander.
 *     In my setup I am using a PNP Transistor connected to 5V unsing 
 *     an resistor, the LED and the Arduino to make sure the LED gets
 *     a current from Vcc and not from the I2C exapander port.
 *  
 *  This code is trying to explain how it works as simple as possible.
 *  More detailed examples are found on the web. Search for pcf8575 and
 *  you will find what you want.
*/

// Set I2C address
int address = 0x20;

void setup(){ 
  Wire.begin();
  // Set all ports as output
  pf575_write(word(B11111111,B11111111));
} 

void loop(){
  // Set port P0 on
  pf575_write(word(B00000000,B00000001));
  delay(1000);
  // Set port P0 off
  pf575_write(word(B00000000,B00000000));
  delay(1000);
} 

// Function for writing two Bytes to the I2C expander device
void pf575_write(uint16_t data) {
  Wire.beginTransmission(address);
  Wire.write(lowByte(data));
  Wire.write(highByte(data));
  Wire.endTransmission();
}

Some links:

Posted in: arduinodiyelectronicsopensource

Tags: arduino, pf575, io, expander, i2c,