IoT Digital Thermometer using NodeMCU and LM35

In this tutorial we will explore more about this interesting MCU and slowly we dive in Internet of things world by connecting NodeMCU with the Internet. Here we will use this module to get room temperature on web browser i.e. we will make a web server to display the temperature using LM35 as temperature sensor.

Components Required:

NodeMCU - ESP12
LM35 Temperature Sensor
Breadboard
Male-female connectors

LM35 Temperature Sensor:

LM35 is a analog linear temperature sensor. Its output is proportional to the temperature (in degree Celsius). The operating temperature range is from -55°C to 150°C. The output voltage varies by 10mV in response to every oC rise or fall in temperature. It can be operated from a 5V as well as 3.3 V supply and the stand by current is less than 60uA.

Note that LM35 is available in 3 series variations namely LM35A, LM35C and LM35D series. The main difference is in their range of temperature measurements. The LM35D series is designed to measure 0 to 100 degree Celsius, where as the LM35A series is designed to measure a wider range of -55 to 155 degree Celsius. The LM35C series is designed to measure from -40 to 110 degree Celsius.

Connecting LM35 with NodeMCU:

Circuit diagram for connecting LM35 with NodeMCU is given below:

LM35 is an analog sensor so we have to convert this analog output to digital. For this we use ADC pin of NodeMCU which is defined as A0. We will connect the output of LM35 to A0.

We have 3.3 V as output voltage on NodeMCU’s pins. So, we will use 3.3V as Vcc for LM35.

Code Explanation:

Complete code with Demonstration Video is given at the end of the article. Here we are explaining few parts of the code. We already explained to upload code into MCU using Arduino IDE.

First, we have to include ESP8266wifi library to access the Wi-Fi functions..

#include <ESP8266WiFi.h>

Then enter your Wi-Fi name and password in ssid and password field. Also initialized the variables and start the server on port 80 with baud rate 115200.

const char* ssid     = "*********"; // Your ssid
const char* password = "***********"; // Your Password
float temp_celsius = 0;
float temp_fahrenheit = 0;
WiFiServer server(80);
void setup() {
 Serial.begin(115200);

Connection of Wi-Fi is established by calling these functions.

Serial.println();
Serial.println();
Serial.print("Connecting to ");
Serial.println(ssid);
WiFi.begin(ssid, password);

Connection can take few seconds to establish so keep showing ‘…’ till connection will not establish. Then system will keep waiting and checking for a client to connect…

while (WiFi.status() != WL_CONNECTED) {
delay(500);
Serial.print(".");
}
Serial.println("");
Serial.println("WiFi is connected");
server.begin();
Serial.println("Server started");
Serial.println(WiFi.localIP());
}

In loop section, read sensor values and convert it into Celsius and Fahrenheit and display these values on serial monitor.

void loop() {
temp_celsius = (analogRead(A0) * 330.0) / 1023.0;   // To convert analog values to Celsius We have 3.3 V on our board and we know that output voltage of LM35 varies by 10 mV to every degree Celsius rise/fall. So , (A0*3300/10)/1023 = celsius
temp_fahrenheit = celsius * 1.8 + 32.0;
Serial.print("  Temperature = ");
Serial.print(temp_celsius);
Serial.print(" Celsius, ");

HTML Code to display Temperature on WebPage:

We are displaying the temperature on a webpage so that it can be accessible from anywhere in the world through internet. HTML code is very simple; we just have to use client.println function to echo each line of the HTML code, so that browser can execute it.

This part shows HTML code to create a web page which displays the temperature value.

WiFiClient client = server.available();
client.println("HTTP/1.1 200 OK");
client.println("Content-Type: text/html");
client.println("Connection: close");  // the connection will be closed after completion of the response
client.println("Refresh: 10");  // update the page after 10 sec
client.println();
client.println("<!DOCTYPE HTML>");
client.println("<html>");
client.print("<p style='text-align: center;'><span style='font-size: x-large;'><strong>Digital Thermometer</strong></span></p>");
client.print("<p style='text-align: center;'><span style='color: #0000ff;'><strong style='font-size: large;'>Temperature (*C)= ");
client.println(temp_celsius);
client.print("<p style='text-align: center;'><span style='color: #0000ff;'><strong style='font-size: large;'>Temperature (F) = ");
client.println(temp_fahrenheit);
client.print("</p>");
client.println("</html>");
delay(5000);
}

Working:

After uploading the code using Arduino IDE, open serial monitor and press the Reset button on NodeMCU.

Now, you can see the board is connected to the Wi-Fi network which you have defined in your code and also you got the IP. Copy this IP and paste it in any web browser. Make sure your system on which you are running the web browser should connected to the same network.

Your digital thermometer is ready and the temperature will be refreshed automatically in web browser after every 10 Sec.

To make this webpage accessible from the internet, you just need to set Port Forwarding in you router/modem.

Code

#include <ESP8266WiFi.h>
const char* ssid = "*********"; // Your ssid
const char* password = "***********"; // Your Password
float temp_celsius = 0;
float temp_fahrenheit = 0;
WiFiServer server(80);
void setup() {
Serial.begin(115200);
pinMode(A0, INPUT);
Serial.println();
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 is connected");
server.begin();
Serial.println("Server started");
Serial.println(WiFi.localIP());
}
void loop() {
temp_celsius = (analogRead(A0) * 330.0) / 1023.0; // To convert analog values to Celsius We have 3.3 V on our board and we know that output voltage of LM35 varies by 10 mV to every degree Celsius rise/fall. So , (A0*3300/10)/1023 = celsius
temp_fahrenheit = celsius * 1.8 + 32.0;
Serial.print(" Temperature = ");
Serial.print(temp_celsius);
Serial.print(" Celsius, ");
Serial.print(temp_fahrenheit);
Serial.println(" Fahrenheit");

WiFiClient client = server.available();
client.println("HTTP/1.1 200 OK");
client.println("Content-Type: text/html");
client.println("Connection: close"); // the connection will be closed after completion of the response
client.println("Refresh: 10"); // update the page after 10 sec
client.println();
client.println("<!DOCTYPE HTML>");
client.println("<html>");
client.print("Digital Thermometer");
client.print("Temperature (*C)= ");
client.println(temp_celsius);
client.print("Temperature (F) = ");
client.println(temp_fahrenheit);
client.print("");
client.println("</html>");
delay(5000);
}

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