expander_test.ino

/*
Pinout:
Connect pin #1 of the expander to Analog 5 (i2c clock)
Connect pin #2 of the expander to Analog 4 (i2c data)
Connect pins #3, 4 and 5 of the expander to ground (address selection)
Connect pin #6 and 18 of the expander to 5V (power and reset disable)
Connect pin #9 of the expander to ground (common ground)
*/

#include <Wire.h>
#include <Adafruit_MCP23008.h> // From plab-libraries

#define PIN_EXPANDER_ADDRESS 0
#define EXPIN_LED 4

Adafruit_MCP23008 expander;

void setup() {
  expander.begin(PIN_EXPANDER_ADDRESS);
  expander.pinMode(EXPIN_LED, OUTPUT);
}

void loop() {
  expander.digitalWrite(EXPIN_LED, LOW);
  delay(500);
  expander.digitalWrite(EXPIN_LED, HIGH);
  delay(500);
}