Arduino PCF8575 8xLED LM35 Thermometer

Sep 24, 2015 (CET)

My code:

#include <Wire.h>

// Set I2C address
int address = 0x20;

int samples = 2;
int collectDelay = 1000;
int ledPin = 13;
int tempPin = 0;

float tempC = 0;

void setup() {
  pinMode(ledPin, OUTPUT);
  Wire.begin();
  pf575_write(word(B11111111,B11111111));
  delay(200);
  pf575_write(word(B00000000,B11111111));
  delay(200);
  pf575_write(word(B11111111,B11111111));
  delay(200);
  pf575_write(word(B00000000,B11111111));
  delay(200);
  pf575_write(word(B11111111,B11111111));
  delay(1000);
}

void loop() {
  tempC = 0;
  for(int i = 0; i <= (samples - 1); i++) {
    tempC = tempC + ((5.0 * analogRead(tempPin) * 100.0) / 1024.0);
    digitalWrite(ledPin, HIGH);
    delay((collectDelay / 2));
    digitalWrite(ledPin, LOW);
    delay((collectDelay / 2));
  }
  tempC = tempC / (float)samples;
  if(tempC > 21) {
    pf575_write(word(B11111110,B11111111));
  }
  if(tempC > 23) {
    pf575_write(word(B11111100,B11111111));
  }
  if(tempC > 25) {
    pf575_write(word(B11111000,B11111111));
  }
  if(tempC > 27) {
    pf575_write(word(B11110000,B11111111));
  }
  if(tempC > 29) {
    pf575_write(word(B11100000,B11111111));
  }
  if(tempC > 31) {
    pf575_write(word(B11000000,B11111111));
  }
  if(tempC > 33) {
    pf575_write(word(B10000000,B11111111));
  }
  if(tempC > 35) {
    pf575_write(word(B00000000,B11111111));
  }
}

void pf575_write(uint16_t data) {
  Wire.beginTransmission(address);
  Wire.write(highByte(data));
  Wire.write(lowByte(data));
  Wire.endTransmission();
}

Arduino PF575 I²C I/O port expander blink example

Sep 23, 2015 (CET)

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.

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

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:

• PCF8575 Datasheet at ti.com
• Tutorial: Arduino I/O Port Expander with PCF8574
• Using The PCF8575 i2c i/o Expander To Read Inputs With Arduino

Website refactored!

Sep 10, 2015 (CET)

I refactored this website last night. Please do not wonder why things are different. Some features are gone, some will come back... I need some time for it but for now I am very excited about the result.

I will update this post from time to time in the next days...