ESP8266 + K-30 CO2 Sensor over UART + DHT22 temperature/humidity sensor + MQTT

ESP8266_K30_DHT.ino

#include <ESP8266WiFi.h>
#include <PubSubClient.h>
#include <DHT.h>

DHT dht(D5, DHT22);

const char* ssid     = "........";
const char* password = "........";

IPAddress mqttServer(192, 168, 1, 10);

WiFiClient mqttTcpClient;
PubSubClient mqttClient(mqttTcpClient, mqttServer);

void setup() {
  delay(1000);
  Serial.begin(9600);
  Serial.swap();
  delay(1000);

  // We start by connecting to a WiFi network
  Serial1.begin(115200);
  Serial1.println();
  Serial1.println();
  Serial1.print("Connecting to ");
  Serial1.println(ssid);
  
  WiFi.begin(ssid, password);
  
  while (WiFi.status() != WL_CONNECTED) {
    delay(500);
    Serial1.print(".");
  }

  Serial1.println("");
  Serial1.println("WiFi connected");  
  Serial1.println("IP address: ");
  Serial1.println(WiFi.localIP());

  String clientName = "arduinoClient";
  clientName += micros();

  for (int retries = 0; retries < 10; ++retries) {
    Serial1.print("connecting to ");
    Serial1.println(mqttServer);
    Serial1.print("Connecting to MQTT broker... as ");
    Serial1.println(clientName);
    if (!mqttClient.connect(clientName))
      continue;      
    Serial1.println("Connect successful");
    break;
  }

}

int value = 0;

void loop() {
  delay(5000);

  Serial1.println("reading co2 level");
  const uint8_t request[] = {0xFE, 0x44, 0x00, 0x08, 0x02, 0x9F, 0x25};
  Serial.write(request, sizeof(request));
  uint8_t response[8];
  int t = millis();
  for (int i = 0; i < 7; ++i) {
    if (Serial.available()) {
      response[i] = Serial.read();
    }
    if (millis() - t > 1000) {
      Serial1.println("no response");
      return;
    }
  }

  int co2value = static_cast<int>(response[3]) * 256 + static_cast<int>(response[4]);
  Serial1.print("co2:");
  Serial1.println(co2value);
  if (co2value > 2000)
    return;
    
  
  mqttClient.publish("/sensor/office/co2", String(co2value));

  float h = dht.readHumidity();
  char buf[20];
  dtostrf(h, 2, 0, buf);
  Serial1.print("humidity:");
  Serial1.println(buf);
  mqttClient.publish("/sensor/office/humidity", String(buf));
  
  float temp = dht.readTemperature();
  dtostrf(temp, 2, 1, buf);
  Serial1.print("temperature:");
  Serial1.println(buf);
  mqttClient.publish("/sensor/office/temperature", String(buf));

}