add binary sensor example

examples/binary-sensor/binary-sensor.ino

@@ -0,0 +1,40 @@
+#include <Ethernet.h>
+#include <ArduinoHA.h>
+
+#define INPUT_PIN 9
+
+byte mac[] = {0x00, 0x10, 0xFA, 0x6E, 0x38, 0x4A};
+unsigned long lastReadAt = millis();
+bool lastInputState = false;
+
+EthernetClient client;
+HADevice device(mac, sizeof(mac));
+HAMqtt mqtt(client, device);
+HABinarySensor sensor("input", "door", false, mqtt);
+
+void setup() {
+    pinMode(INPUT_PIN, INPUT_PULLUP);
+    lastInputState = digitalRead(INPUT_PIN);
+
+    // you don't need to verify return status
+    Ethernet.begin(mac);
+
+    // set device's details (optional)
+    device.setName("Arduino");
+    device.setSoftwareVersion("1.0.0");
+
+    // please change IP address to yours
+    mqtt.begin(IPAddress(192,168,0,17));
+}
+
+void loop() {
+    Ethernet.maintain();
+    mqtt.loop();
+
+    if ((millis() - lastReadAt) > 30) { // read in 30ms interval
+        // library produces MQTT message if a new state is different than the previous one
+        sensor.setState(digitalRead(INPUT_PIN));
+        lastInputState = sensor.getState();
+        lastReadAt = millis();
+    }
+}