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Practical Guide to PCF8574: Adding Extra Pins for Arduino

Add extra 8 pins to Arduino !

IntermediateProtip2 hours343
Practical Guide to PCF8574: Adding Extra Pins for Arduino

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Schematics

I2C connection of IO expander

Code

Controlling 7segment display using PCF 8574 expander and the pushbutton without interrupts

Arduino
Code without using interrupts
#include "Arduino.h"
#include "PCF8574.h"

PCF8574 pcf8574(0x21);

int digits [10][7]{
  {1,1,1,1,1,1,0}, // digit 0
  {0,1,1,0,0,0,0}, // digit 1
  {1,1,0,1,1,0,1}, // digit 2
  {1,1,1,1,0,0,1}, // digit 3
  {0,1,1,0,0,1,1}, // digit 4
  {1,0,1,1,0,1,1}, // digit 5
  {1,0,1,1,1,1,1}, // digit 6
  {1,1,1,0,0,0,0}, // digit 7
  {1,1,1,1,1,1,1}, // digit 8
  {1,1,1,1,0,1,1}  // digit 9
};

int i=0;
#define SEG_A  P5
#define SEG_B  P4
#define SEG_C  P1
#define SEG_D  P2
#define SEG_E  P3
#define SEG_F  P6
#define SEG_G  P7
#define Button  P0

void display_digit(int d){
  if (digits[d][0]==1) pcf8574.digitalWrite(SEG_A,LOW); else pcf8574.digitalWrite(SEG_A,HIGH); //A
  if (digits[d][1]==1) pcf8574.digitalWrite(SEG_B,LOW); else pcf8574.digitalWrite(SEG_B,HIGH); //B
  if (digits[d][2]==1) pcf8574.digitalWrite(SEG_C,LOW); else pcf8574.digitalWrite(SEG_C,HIGH); //C
  if (digits[d][3]==1) pcf8574.digitalWrite(SEG_D,LOW); else pcf8574.digitalWrite(SEG_D,HIGH); //D
  if (digits[d][4]==1) pcf8574.digitalWrite(SEG_E,LOW); else pcf8574.digitalWrite(SEG_E,HIGH); //E
  if (digits[d][5]==1) pcf8574.digitalWrite(SEG_F,LOW); else pcf8574.digitalWrite(SEG_F,HIGH); //F
  if (digits[d][6]==1) pcf8574.digitalWrite(SEG_G,LOW); else pcf8574.digitalWrite(SEG_G,HIGH); //G
} 


void setup() {
  Serial.begin(9600);
  pcf8574.pinMode(SEG_A, OUTPUT);
  pcf8574.pinMode(SEG_B, OUTPUT);
  pcf8574.pinMode(SEG_C, OUTPUT);
  pcf8574.pinMode(SEG_D, OUTPUT);
  pcf8574.pinMode(SEG_E, OUTPUT);
  pcf8574.pinMode(SEG_F, OUTPUT);
  pcf8574.pinMode(SEG_G, OUTPUT);
  pcf8574.pinMode(Button, INPUT_PULLUP);
  if(pcf8574.begin())
     Serial.println("OK");
     else Serial.println("Failed");
}
void loop() {
   int button_pressed=pcf8574.digitalRead(P0);
   Serial.println(button_pressed);
   if (button_pressed==LOW){
    i=i+1;
    if(i>9) i=0;
   } 
   delay(1000); 
   display_digit(i);
}

Blinking 2 LEDs

Arduino
One led is controlled from Arduino pin and the other one is controlled from Expander pin
#include "Arduino.h"
#include "PCF8574.h"
PCF8574 pcf8574(0x21);

#define LED_PIN_ARDUINO  3
#define LED_PIN_PCF8574  P6


void setup() {
  Serial.begin(9600);
  if(pcf8574.begin())
     Serial.println("OK");
     else Serial.println("Failed");
  pcf8574.pinMode(P2, INPUT_PULLUP);
  pcf8574.pinMode(LED_PIN_PCF8574, OUTPUT);
}
void loop() {
  digitalWrite(LED_PIN_ARDUINO, HIGH);
  pcf8574.digitalWrite(LED_PIN_PCF8574, LOW);  
  delay(1000);
  digitalWrite(LED_PIN_ARDUINO, LOW);
  pcf8574.digitalWrite(LED_PIN_PCF8574, HIGH);
  delay(1000);
}

Controlling 7 segmet display

Arduino
Controlling the display using 7 expander pins. The code is displaying digits from 0 to 9 in 1s intervals
#include "Arduino.h"
#include "PCF8574.h"

PCF8574 pcf8574(0x21);

int digits [10][7]{
  {1,1,1,1,1,1,0}, // digit 0
  {0,1,1,0,0,0,0}, // digit 1
  {1,1,0,1,1,0,1}, // digit 2
  {1,1,1,1,0,0,1}, // digit 3
  {0,1,1,0,0,1,1}, // digit 4
  {1,0,1,1,0,1,1}, // digit 5
  {1,0,1,1,1,1,1}, // digit 6
  {1,1,1,0,0,0,0}, // digit 7
  {1,1,1,1,1,1,1}, // digit 8
  {1,1,1,1,0,1,1}  // digit 9
};


#define SEG_A  P5
#define SEG_B  P4
#define SEG_C  P1
#define SEG_D  P2
#define SEG_E  P3
#define SEG_F  P6
#define SEG_G  P7

void display_digit(int d){
  if (digits[d][0]==1) pcf8574.digitalWrite(SEG_A,LOW); else pcf8574.digitalWrite(SEG_A,HIGH); //A
  if (digits[d][1]==1) pcf8574.digitalWrite(SEG_B,LOW); else pcf8574.digitalWrite(SEG_B,HIGH); //B
  if (digits[d][2]==1) pcf8574.digitalWrite(SEG_C,LOW); else pcf8574.digitalWrite(SEG_C,HIGH); //C
  if (digits[d][3]==1) pcf8574.digitalWrite(SEG_D,LOW); else pcf8574.digitalWrite(SEG_D,HIGH); //D
  if (digits[d][4]==1) pcf8574.digitalWrite(SEG_E,LOW); else pcf8574.digitalWrite(SEG_E,HIGH); //E
  if (digits[d][5]==1) pcf8574.digitalWrite(SEG_F,LOW); else pcf8574.digitalWrite(SEG_F,HIGH); //F
  if (digits[d][6]==1) pcf8574.digitalWrite(SEG_G,LOW); else pcf8574.digitalWrite(SEG_G,HIGH); //G
} 


void setup() {
  Serial.begin(9600);
  if(pcf8574.begin())
     Serial.println("OK");
     else Serial.println("Failed");

  pcf8574.pinMode(SEG_A, OUTPUT);
  pcf8574.pinMode(SEG_B, OUTPUT);
  pcf8574.pinMode(SEG_C, OUTPUT);
  pcf8574.pinMode(SEG_D, OUTPUT);
  pcf8574.pinMode(SEG_E, OUTPUT);
  pcf8574.pinMode(SEG_F, OUTPUT);
  pcf8574.pinMode(SEG_G, OUTPUT);
}
void loop() {
   for (int i=0;i<10;i++) {
   display_digit(i);
   delay(1000);
  }

}

Controlling 7segment display using PCF 8574 expander and the pushbutton witt interrupts

Arduino
Code with interrupts
#include "Arduino.h"
#include "PCF8574.h"

// For arduino uno only pin 1 and 2 are interrupted
#define ARDUINO_UNO_INTERRUPTED_PIN 2

// Function interrupt
void keyPressedOnPCF8574();

PCF8574 pcf8574(0x21, ARDUINO_UNO_INTERRUPTED_PIN, keyPressedOnPCF8574);

int digits [10][7]{
  {1,1,1,1,1,1,0}, // digit 0
  {0,1,1,0,0,0,0}, // digit 1
  {1,1,0,1,1,0,1}, // digit 2
  {1,1,1,1,0,0,1}, // digit 3
  {0,1,1,0,0,1,1}, // digit 4
  {1,0,1,1,0,1,1}, // digit 5
  {1,0,1,1,1,1,1}, // digit 6
  {1,1,1,0,0,0,0}, // digit 7
  {1,1,1,1,1,1,1}, // digit 8
  {1,1,1,1,0,1,1}  // digit 9
};

int i=0;
unsigned long timeElapsed;
#define SEG_A  P5
#define SEG_B  P4
#define SEG_C  P1
#define SEG_D  P2
#define SEG_E  P3
#define SEG_F  P6
#define SEG_G  P7
#define Button  P0

void display_digit(int d){
  if (digits[d][0]==1) pcf8574.digitalWrite(SEG_A,LOW); else pcf8574.digitalWrite(SEG_A,HIGH); //A
  if (digits[d][1]==1) pcf8574.digitalWrite(SEG_B,LOW); else pcf8574.digitalWrite(SEG_B,HIGH); //B
  if (digits[d][2]==1) pcf8574.digitalWrite(SEG_C,LOW); else pcf8574.digitalWrite(SEG_C,HIGH); //C
  if (digits[d][3]==1) pcf8574.digitalWrite(SEG_D,LOW); else pcf8574.digitalWrite(SEG_D,HIGH); //D
  if (digits[d][4]==1) pcf8574.digitalWrite(SEG_E,LOW); else pcf8574.digitalWrite(SEG_E,HIGH); //E
  if (digits[d][5]==1) pcf8574.digitalWrite(SEG_F,LOW); else pcf8574.digitalWrite(SEG_F,HIGH); //F
  if (digits[d][6]==1) pcf8574.digitalWrite(SEG_G,LOW); else pcf8574.digitalWrite(SEG_G,HIGH); //G
} 


void setup() {
  Serial.begin(9600);
  timeElapsed=millis();
  pcf8574.pinMode(SEG_A, OUTPUT);
  pcf8574.pinMode(SEG_B, OUTPUT);
  pcf8574.pinMode(SEG_C, OUTPUT);
  pcf8574.pinMode(SEG_D, OUTPUT);
  pcf8574.pinMode(SEG_E, OUTPUT);
  pcf8574.pinMode(SEG_F, OUTPUT);
  pcf8574.pinMode(SEG_G, OUTPUT);
  pcf8574.pinMode(Button, INPUT_PULLUP);
  if(pcf8574.begin())
     Serial.println("OK");
     else Serial.println("Failed");
}
void loop() {
  display_digit(i);
}

void keyPressedOnPCF8574(){
   if (millis()-timeElapsed>300){
     i=i+1;if(i>9) i=0;
     timeElapsed=millis();
   }
}

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mdraber

mdraber

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