Arduino Mega

#include <Adafruit_Sensor.h>
#include <DHT.h>
#include <DHT_U.h>


String s = "";
String readInput;

//Temp Sensor
#define DHT11_PIN 31
DHT dht(DHT11_PIN, DHT11);
int curTemp = 68;
int curHumidity = 30;

void setup() {

  //Serial3 (NOTICE THE "3") is where/how the Mega & ESP will communicate, and it's important to run it slow, e.g. 9600
  Serial3.begin(9600);

  //this is just normal serial output (e.g. Serial Monitor)
  Serial.begin(115200);
  Serial.println("Mega Ready to rock!  Starting loop:");
}

String readString;
int cnt = 0;
int testValueToESP = 100;

int loopCnt_SensorsReport = 0;
int loopCntDelay_SensorsReport = 120000;

void loop() {

  //this listens for INCOMING message from the ESP.  If an incoming msg exists, it compiles it into a string
  char incomingByte;
  while (Serial3.available() > 0)
  {
    delay(10); //if the data came
    incomingByte = Serial3.read(); //read byte
    readString += incomingByte;
  }

  //if there was a new message, we act on it.  In this case we are just turning on/off the built-in LED.
  //couple things to note here that really threw me for a loop:
  //  notice the .equals comparison method, I found this to be necessary
  //  notice the 1\r\n and 0\r\n values I'm comparing.  It wasn't until I realized the \r\n (carriage return
  //         & new line where included) that I got the comparisons to work properly
  if (readString != "") {
    Serial.print("received this: ");
    Serial.println(readString);

    if (readString.equals("1\r\n")) {
      Serial.println("turning on BUILTIN LED");
      digitalWrite(LED_BUILTIN, HIGH);
    } else if (readString.equals("0\r\n")) {
      Serial.println("turning off BUILTIN LED");
      digitalWrite(LED_BUILTIN, LOW);
    } else {
      Serial.print("unhandled event: ");
      Serial.println(readString);
    }
  }

  //clear the incoming message so we don't act on it again
  readString = "";

  //every ~10k milliseconds, let's sent a # to the ESP (this was just a simple communications test)
  if (cnt <= 10000) {
    cnt++;
    delay(1);
  } else {
    cnt = 0;
    testValueToESP++;
    Serial3.print("t: ");
    Serial3.println(testValueToESP);
  }

  //at a regular interval, let's read the temp & humidity sensor, serialize the info into JSON, and send it to the ESP so it
  //can do something interesting with the sensor data, like log it to a database.
  loopCnt_SensorsReport++;
  if (loopCnt_SensorsReport > loopCntDelay_SensorsReport)
  {
    Serial.println("loopCntDelay_SensorsReport hit!");
    curTemp = dht.readTemperature(true);
    curHumidity = dht.readHumidity();

    loopCnt_SensorsReport = 0; //reset

    //construct some JSON
    String sensorRpt = "{ 'Type': 'SensorReport', 'Temp': " + String(curTemp) + ", 'Humdity': " + String(curHumidity) + "}";

    //send the JSON to the ESP
    Serial3.println(sensorRpt);

  }

  //this was for my personal testing to slow things down, but obviously it's currently at "0"
  delay(0);
}

//end of Mega sketch