Temperature sensor help (ESP8266) (LoRa) (Blynk)

I’m trying to make a temperature sensor device which detects and sends an email/sms message to the user when the temperature near the device exceeds 40 degrees. To do this, the main components of my circuit design include 2 halves, the transmitter and receiver sides. The transmitter side include the temperature sensor, an LM75 voltage regulator, and Arduino Nano and a LoRa transmitter. The receiver side uses a buzzer, LoRa receiver module and an ESP8266 mini WI-FI module. I used open source code to program the circuits and I have followed all the instructions given, I personally think it’s an issue to do with the soldering quality or a physical wire connection issue, however, I just wanna make sure it isn’t anything else before I star dismantling the circuit.

The issue I’ve been having is that when I try to connect the esp8266 wifi module to the blynk app, the device name consistently has an offline symbol next to it. I have tried updating the libraries, checking the Wi-Fi id and password, etc but nothing is working and I don’t even thing that it’s connected to my android phone at least. I’m from the UK and I have pasted my entire code below for both the transmitter and receiver side.

Transmitter Side:

// I2C Temperature Sensors derived from the LM75 - Version: Latest 
#include <Temperature_LM75_Derived.h>

//Lora with Transmitter arduino nano

#include <SPI.h>              // include libraries
#include <LoRa.h>
 #include <Wire.h>
#include <Adafruit_GFX.h>
#include <LM75A.h>
#include <Adafruit_SSD1306.h>
LM75A lm75a_sensor(false,  // A0 LM75A pin state (connected to ground = false)
                   false,  // A1 LM75A pin state (connected to ground = false)
                   false); // A2 LM75A pin state (connected to ground = false)
// Equivalent to "LM75A lm75a_sensor;"

#define SCREEN_WIDTH 128 // OLED display width, in pixels
#define SCREEN_HEIGHT 64 // OLED display height, in pixels

// Declaration for an SSD1306 display connected to I2C (SDA, SCL pins)
#define OLED_RESET     -1 // Reset pin # (or -1 if sharing Arduino reset pin)

String outgoing;              // outgoing message
byte msgCount = 0;            // count of outgoing messages
byte MasterNode = 0xFF;     
byte Node1 = 0xBB;
float ctemp; 
float ftemp;
String Mymessage = "";
void setup() {
  Serial.begin(9600);                   // initialize serial
  if (!LoRa.begin(433E6)) {       
    Serial.println("LoRa init failed. Check your connections.");
    while (true);                       // if failed, do nothing
display.begin(SSD1306_SWITCHCAPVCC, 0x3C);
void loop() {
  float temperature_in_degrees = lm75a_sensor.getTemperatureInDegrees();

  if (temperature_in_degrees == INVALID_LM75A_TEMPERATURE)
    Serial.println("Error while getting temperature");
//    Serial.print("Temperature: ");
//    Serial.print(temperature_in_degrees);
//    Serial.print(" degrees ");
    ftemp= LM75A::degreesToFahrenheit(temperature_in_degrees);
//    Serial.print(ftemp);
//    Serial.println(" fahrenheit)");
  display.println(" Temperature");
  //display.print("C: ");
  //display.print("F: ");

    Mymessage = Mymessage + temperature_in_degrees + "," + ftemp;  
    Mymessage = "";
void sendMessage(String outgoing, byte MasterNode, byte otherNode) {
  LoRa.beginPacket();                   // start packet
  LoRa.write(MasterNode);              // add destination address
  LoRa.write(Node1);             // add sender address
  LoRa.write(msgCount);                 // add message ID
  LoRa.write(outgoing.length());        // add payload length
  LoRa.print(outgoing);                 // add payload
  LoRa.endPacket();                     // finish packet and send it
  msgCount++;                           // increment message ID

Receiver Side:

// Blynk - Version: Latest 

// Blynk - Version: Latest 
#include <BlynkSimpleEsp8266.h>
#define BLYNK_TEMPLATE_ID "blynk template id"
#define BLYNK_AUTH_TOKEN "auth token"
 ESP8266 LoRa Gateway, receiver side

#include <SPI.h>              // include libraries
#include <LoRa.h>
#include <Wire.h>
#include <Blynk.h>

#define Nss 15 // D8 pin CS
#define rst 16 // D0 
#define dio0 2 // D4
int buzzer = D3;
char auth[] = "-HrsXL8bXKhJrZdFOmVQgK6VfzGoVQqv";

 ///Connect SCL to D1 and Connect SDA to D2
/* WiFi credentials */
char ssid[] = "network name";
char pass[] = "password";

byte MasterNode = 0xFF;     
byte Node1 = 0xBB;
String SenderNode = "";
String outgoing;              // outgoing message
byte msgCount = 0;            // count of outgoing messages
String incoming = "";
float ctemp; 
float ftemp; 

void setup() {
  Serial.begin(9600);                   // initialize serial
 LoRa.setPins(Nss, rst, dio0);

  if (!LoRa.begin(433E6)) {             // initialize ratio at 915 MHz
    Serial.println("LoRa init failed. Check your connections.");
    while (true);                       // if failed, do nothing

 // Serial.println("LoRa init succeeded.");
   Blynk.begin(auth, ssid, pass);


void loop() {
  // parse for a packet, and call onReceive with the result:

void onReceive(int packetSize) {
  if (packetSize == 0) return;          // if there's no packet, return

  // read packet header bytes:
  int recipient = LoRa.read();          // recipient address
  byte sender = LoRa.read();            // sender address
  if( sender == 0XBB )
  SenderNode = "Node1:";
  byte incomingMsgId = LoRa.read();     // incoming msg ID
  byte incomingLength = LoRa.read();    // incoming msg length

  while (LoRa.available()) {
    incoming += (char)LoRa.read();

  if (incomingLength != incoming.length()) {   // check length for error
    //Serial.println("error: message length does not match length");
    return;                             // skip rest of function

  // if the recipient isn't this device or broadcast,
  if (recipient != Node1 && recipient != MasterNode) {
   // Serial.println("This message is not for me.");
    return;                             // skip rest of function

  // if message is for this device, or broadcast, print details:
  //Serial.println("Received from: 0x" + String(sender, HEX));
  //Serial.println("Sent to: 0x" + String(recipient, HEX));
  //Serial.println("Message ID: " + String(incomingMsgId));
 // Serial.println("Message length: " + String(incomingLength));
 // Serial.println("Message: " + incoming);
  //Serial.println("RSSI: " + String(LoRa.packetRssi()));
 // Serial.println("Snr: " + String(LoRa.packetSnr()));
 // Serial.println();

 String q=getValue(incoming, ',', 0); 
String r =getValue(incoming, ',', 1); 
ctemp = q.toFloat();
  Serial.println(" C");
ftemp = r.toFloat();
  Serial.println(" F");
 if (ctemp >= 40 )
      Blynk.notify("Temperature Exceeded!!!"); 
      digitalWrite( buzzer, HIGH);
  if (ctemp < 40 )
      digitalWrite( buzzer, LOW);

incoming = "";


String getValue(String data, char separator, int index)
    int found = 0;
    int strIndex[] = { 0, -1 };
    int maxIndex = data.length() - 1;
    for (int i = 0; i <= maxIndex && found <= index; i++) {
        if (data.charAt(i) == separator || i == maxIndex) {
            strIndex[0] = strIndex[1] + 1;
            strIndex[1] = (i == maxIndex) ? i+1 : i;
    return found > index ? data.substring(strIndex[0], strIndex[1]) : "";

A few comments from me about your “Transmitter Side:” code…

It’s always a good idea to have these three line of configuration as the very first lines of code in your sketch. In the past, some versions of the Blynk library have insisted on this, the current version doesn’t bit it’s still good practice…

You should then have #define BLYNK_PRINT Serial as the next line of code. This sirects all Blynk debug and information messages to your serial monitor.

It’s also a good idea to use a serial baud rate that is the same as the native board rate of your development board, so that you can see the boot messages from the chip, as well as the Blynk and serial print messages at the same time without having to change the baud rate setting in the serial monitor.
Your board probably has a baud rate of 74880, so change this line:

from 9600 to 74880.

This line should be deleted…

and so should this…

You then need to change this…

to this…

Blynk.begin(BLYNK_AUTH_TOKEN , ssid, pass);

that way you are using the correct Blynk auth token that you copies from your firmware configuration screen.

It;'s also good practice to use GPIO numbers, not their “D” aliases, and you certainly shouldn’t mix the two up like you do here…

Change int buzzer = D3; to int buzzer = 0 // D3;

But, using pin GPIO 0 (D3) is a really bad idea, because if this pin is pulled LOW at boot-up the board will not boot.
Take a look at the “Best pins to use” table in this tutorial…

Once you’ve made those changes and re-flashed your ESP8266 take a look at your serial monitor (set to 74880) and you’ll have an insight into what is happening when your board boots and attempts to connect to Blynk.