ESP8266-based power meter in Kibana

#include <Arduino.h>
#include <ESP8266WiFi.h>
#include <PubSubClient.h>
#include "DHT.h"
#include <TM1637Display.h>

#define DHTPIN D
#define DHTTYPE DHT11

#define SEGCLK 2
#define SEGDIO 3

const char* ssid = "xxx";
const char* password = "yyy";
const char* mqtt_server = "mqtt.int.mtak.nl";

const char* dhtTopic = "meterkast/dht";
const char* ldrTopic = "meterkast/power";

WiFiClient espClient;
PubSubClient client(espClient);
DHT dht(DHTPIN, DHTTYPE);
TM1637Display display(SEGCLK, SEGDIO);

long lastDht = 0;
char msg[50];
long lastLdrTime = 0;
long lastLdrUpdate = 0;
long lastDisplayUpdate = 0;
int lastDisplayState = 0;
int lastPower = 0;
int lastTemp = 0;

void setup() {
  pinMode(BUILTIN_LED, OUTPUT);     // Initialize the BUILTIN_LED pin as an output
  digitalWrite(BUILTIN_LED ,0);     // Turn LED on while starting

  uint8_t data[] = { 0xff, 0xff, 0xff, 0xff };
  display.setBrightness(0x0f);
  display.setSegments(data);
  
  Serial.begin(115200);
  setup_wifi();
  client.setServer(mqtt_server, 1883);
  client.setCallback(callback);

  dht.begin();
  digitalWrite(BUILTIN_LED ,HIGH);     // Turn LED off
}

void setup_wifi() {

  delay(10);
  // We start by connecting to a WiFi network
  Serial.println();
  Serial.print("Connecting to ");
  Serial.println(ssid);

  WiFi.begin(ssid, password);

  while (WiFi.status() != WL_CONNECTED) {
    delay(500);
    Serial.print(".");
  }

  Serial.println("");
  Serial.println("WiFi connected");
  Serial.println("IP address: ");
  Serial.println(WiFi.localIP());
}

void callback(char* topic, byte* payload, unsigned int length) {
  Serial.print("Message arrived [");
  Serial.print(topic);
  Serial.print("] ");
  for (int i = 0; i < length; i++) {
    Serial.print((char)payload[i]);
  }
  Serial.println();

}

void reconnect() {
  // Loop until we're reconnected
  while (!client.connected()) {
    Serial.print("Attempting MQTT connection...");
    // Attempt to connect
    if (client.connect("client_identifier", "mqtt_username", "mqtt_password")) {
      Serial.println("connected");
    } else {
      Serial.print("failed, rc=");
      Serial.print(client.state());
      Serial.println(" try again in 5 seconds");
      // Wait 5 seconds before retrying
      delay(5000);
    }
  }
}

void sendDhtSensor() {
  float h = dht.readHumidity();
  float t = dht.readTemperature();

  if (isnan(h) || isnan(t)) {
    Serial.println("Failed to read from DHT sensor!");
    client.publish("dhtTopic", "Failed to read from DHT sensor");
    return;
  }

  char dhtMessage[120];
  sprintf(dhtMessage, "{ \"temperature\": %d, \"humidity\": %d }", round(t), round(h));
  lastTemp = round(t);

  Serial.print("Publish message: ");
  Serial.println(dhtMessage);
  
  client.publish(dhtTopic, dhtMessage);
}

void sendPower(long ldrTime) {
  float watts;

  watts = 3600000 / ldrTime;
  
  char ldrMessage[120];
  sprintf(ldrMessage, "{ \"power\": %d }", round(watts) );
  lastPower = round(watts);
  
  Serial.print("Publish message: ");
  Serial.println(ldrMessage);
  
  client.publish(ldrTopic, ldrMessage);
}
void loop() {

  if (!client.connected()) {
    reconnect();
  }
  client.loop();

  long now = millis();

  // Send DHT sensor data every 60s
  if (now - lastDht > 60000) {
    lastDht = now;
    sendDhtSensor();
  }

  // Only read every 20ms
  //currentTime = millis();
  if ( lastLdrUpdate < ( now - 20 ) ) {
    lastLdrUpdate = now;
    
    // Send power data when necessary (threshold = 200)
    long ldrValue;
    ldrValue = analogRead(A0);
    if ( ldrValue > 200 ) {
      long ldrNow = millis();
    
      long ldrTime;
      ldrTime = ldrNow - lastLdrTime;
    
      // Skip double detections
      if ( ldrTime < 500 ) { return; }
    
      lastLdrTime = ldrNow;
      sendPower(ldrTime);
    }

  }  // lastLdrUpdate < 20ms 
}