arduino-home-assistant/examples/sensor/sensor.ino

#include <Ethernet.h>
#include <ArduinoHA.h>

#define BROKER_ADDR IPAddress(192,168,0,17)

byte mac[] = {0x00, 0x10, 0xFA, 0x6E, 0x38, 0x4A};
unsigned long lastSentAt = millis();
double lastValue = 0;

EthernetClient client;
HADevice device(mac, sizeof(mac));
HAMqtt mqtt(client, device);
HASensor temp("temp"); // "temp" is unique ID of the sensor. You should define your own ID.

void onBeforeSwitchStateChanged(bool state, HASwitch* s)
{
    // this callback will be called before publishing new state to HA
    // in some cases there may be delay before onStateChanged is called due to network latency
}

void setup() {
    // you don't need to verify return status
    Ethernet.begin(mac);

    // set device's details (optional)
    device.setName("Arduino");
    device.setSoftwareVersion("1.0.0");

    // configure sensor (optional)
    temp.setUnitOfMeasurement("°C");
    temp.setDeviceClass("temperature");
    temp.setIcon("mdi:home");
    temp.setName("Home temperature");

    mqtt.begin(BROKER_ADDR);
}

void loop() {
    Ethernet.maintain();
    mqtt.loop();

    if ((millis() - lastSentAt) >= 5000) {
        lastSentAt = millis();
        lastValue = lastValue + 0.5;
        temp.setValue(lastValue);

        // Supported data types:
        // uint32_t (uint16_t, uint8_t)
        // int32_t (int16_t, int8_t)
        // double
        // float
        // const char*
    }
}