Add 8575 examples.

.gitignore

@@ -2,3 +2,4 @@ Doxyfile
 .vscode/
 html/
 .DS_Store
+.idea

examples/pcf8575_blink16leds/pcf8574_blink8leds.ino

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+#include <Adafruit_PCF8575.h>
+
+/* Example for 16 output LEDs that are connected from power to the GPIO expander pins
+ * Note the LEDs must be connected with the CATHODES to the expander, to SINK current!
+ * The PCF8575 cannot SOURCE current!
+ */
+
+Adafruit_PCF8574 pcf;
+
+void setup() {
+  while (!Serial) { delay(10); }
+  Serial.begin(115200);
+  Serial.println("Adafruit PCF8575 LED blink test");
+
+  if (!pcf.begin(0x20, &Wire)) {
+    Serial.println("Couldn't find PCF8575");
+    while (1);
+  }
+  for (uint8_t p=0; p<16; p++) {
+    pcf.pinMode(p, OUTPUT);
+  }
+}
+
+void loop() {
+  for (uint8_t p=0; p<16; p++) {
+    pcf.digitalWrite(p, LOW);  // turn LED on by sinking current to ground
+    delay(100);
+    pcf.digitalWrite(p, HIGH); // turn LED off by turning off sinking transistor
+  }
+}

examples/pcf8575_blinkled/pcf8574_blinkled.ino

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+#include <Adafruit_PCF8575.h>
+
+/* Example for 1 output LED that is connected from power to the GPIO expander pin #7
+ * Note the LEDs must be connected with the CATHODES to the expander, to SINK current!
+ * The PCF8575 cannot SOURCE current!
+ */
+
+Adafruit_PCF8575 pcf;
+
+void setup() {
+  while (!Serial) { delay(10); }
+  Serial.begin(115200);
+  Serial.println("Adafruit PCF8575 LED blink test");
+
+  if (!pcf.begin(0x20, &Wire)) {
+    Serial.println("Couldn't find PCF8575");
+    while (1);
+  }
+  pcf.pinMode(7, OUTPUT);
+}
+
+void loop() {
+  pcf.digitalWrite(7, LOW);  // turn LED on by sinking current to ground
+  delay(100);
+  pcf.digitalWrite(7, HIGH); // turn LED off by turning off sinking transistor
+  delay(100);
+}

examples/pcf8575_buttonledirq/pcf8574_buttonledirq.ino

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+#include <Adafruit_PCF8575.h>
+
+/* Example for 1 button that is connected from PCF GPIO #0 to ground, 
+ * and one LED connected from power to PCF GPIO #7
+ * We also have the IRQ output connected to an Interrupt input pin on the 
+ * Arduino so we are not constantly polling from the PCF8575 expander
+ */
+
+Adafruit_PCF8575 pcf;
+
+#define PCF_BUTTON  0  // on the GPIO expander!
+#define PCF_LED     7  // on the GPIO expander!
+
+#define ARDUINO_IRQ 2  // make sure this pin is possible to make IRQ input
+
+void setup() {
+  while (!Serial) { delay(10); }
+  Serial.begin(115200);
+  Serial.println("Adafruit PCF8575 button/led IRQ test");
+
+  if (!pcf.begin(0x20, &Wire)) {
+    Serial.println("Couldn't find PCF8575");
+    while (1);
+  }
+
+  pcf.pinMode(PCF_BUTTON, INPUT_PULLUP);
+  pcf.pinMode(PCF_LED, OUTPUT);
+  pinMode(LED_BUILTIN, OUTPUT);
+  digitalWrite(LED_BUILTIN, LOW);
+
+  // set up the interrupt pin on IRQ signal toggle
+  pinMode(ARDUINO_IRQ, INPUT_PULLUP);
+  attachInterrupt(digitalPinToInterrupt(ARDUINO_IRQ), button_detect, CHANGE);
+}
+
+// We use a flag to make sure we don't enter the interrupt more than once
+volatile bool in_irq = false;
+
+// called when the button is pressed!
+void button_detect(void) {
+  if (in_irq) return; // we are already handling an irq so don't collide!
+  
+  in_irq = true;
+  interrupts(); // Arduino UNO seems to require that we turn on interrupts for I2C to work!
+  bool val = pcf.digitalRead(PCF_BUTTON);
+  pcf.digitalWrite(PCF_LED, val);
+  in_irq = false;
+}
+
+void loop() {
+  delay(100); // we do nothing here!
+}

examples/pcf8575_read16buttons/pcf8574_read8buttons.ino

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+#include <Adafruit_PCF8575.h>
+
+/* Example for 16 input buttons that are connected from the GPIO expander pins to ground.
+ * Note the buttons must be connected with the other side of the switch to GROUND. There is
+ * a built in pull-up 'resistor' on each input, but no pull-down resistor capability.
+ */
+
+Adafruit_PCF8575 pcf;
+
+void setup() {
+  while (!Serial) { delay(10); }
+  Serial.begin(115200);
+  Serial.println("Adafruit PCF8575 button read test");
+
+  if (!pcf.begin(0x20, &Wire)) {
+    Serial.println("Couldn't find PCF8575");
+    while (1);
+  }
+  for (uint8_t p=0; p<16; p++) {
+    pcf.pinMode(p, INPUT_PULLUP);
+  }
+}
+
+void loop() {
+  for (uint8_t p=0; p<16; p++) {
+    if (! pcf.digitalRead(p)) {
+      Serial.print("Button on GPIO #");
+      Serial.print(p);
+      Serial.println(" pressed!");
+    }
+  }
+  delay(10); // a short debounce delay
+}