The Code
The first thing you will need to do is to include all the necessary libraries as follows:
#include <Arduino.h>
#include <ESP8266WiFi.h>
#include <Hash.h>
#include <ESPAsyncTCP.h>
#include <ESPAsyncWebServer.h>
#include <OneWire.h>
#include <DallasTemperature.h>
Declare the GPIO pin that is connected to the DS18B20 sensor. In our case we are connecting to GPIO 4 (D1):
#define ONE_WIRE_BUS 4
Instantiate the instances needed to initialize the sensor:
// Setup a oneWire instance to communicate with any OneWire devices
OneWire oneWire(ONE_WIRE_BUS);
// Pass our oneWire reference to Dallas Temperature sensor
DallasTemperature sensors(&oneWire);
Setup your network credentials:
const char* ssid = "REPLACE_WITH_YOUR_SSID";
const char* password = "REPLACE_WITH_YOUR_PASSWORD";
Create an AsyncWebServer object on port 80:
AsyncWebServer server(80);
Using the following, read the temperature:
String readDSTemperatureC() {
// Call sensors.requestTemperatures() to issue a global temperature and Requests to all devices on the bus
sensors.requestTemperatures();
float tempC = sensors.getTempCByIndex(0);
if(tempC == -127.00){
Serial.println("Failed to read from DS18B20 sensor");
return "--";
} else {
Serial.print("Temperature Celsius: ");
Serial.println(tempC);
}
return String(tempC);
}
In case the sensor is not able to get a valid reading, it returns -127. So, we have an if statement that returns two dashes (–-) in case the sensor fails to get the readings.
if(tempC == -127.00){
Serial.println("Failed to read from DS18B20 sensor");
return "--";
The reaDSTemperatureF() function works in a similar way but returns the readings in Fahrenheit degrees.
The readings are returned as string type. To convert a float to a string, use the String() function.
return String(tempC);
The next step is building the web page. The HTML and CSS needed to build the web page are saved on the index_html variable.
In the HTML text we have TEMPERATUREC and TEMPERATUREF between % signs. This is a placeholder for the temperature values.
This means that this %TEMPERATUREC% text is like a variable that will be replaced by the actual temperature value from the sensor. The placeholders on the HTML text should go between % signs.
Processor
The next will be to create a processor function that will replace the placeholders in our HTML text with the actual temperature values.
String processor(const String& var){
//Serial.println(var);
if(var == "TEMPERATUREC"){
return readDSTemperatureC();
}
else if(var == "TEMPERATUREF"){
return readDSTemperatureF();
}
return String();
}
When the web page is requested, we check if the HTML has any placeholders. If it finds the %TEMPERATUREC% placeholder, we return the temperature in Celsius by calling the readDSTemperatureC() function created previously.
if(var == "TEMPERATUREC"){
return readDSTemperatureC();
}
If the placeholder is %TEMPERATUREF%, we return the temperature in Fahrenheit.
else if(var == "TEMPERATUREF"){
return readDSTemperatureF();
}
In the setup function, initialise the serial monitor for debugging:
Serial.begin(115200);
Initialise the DS18B20 temperature sensor:
sensors.begin();
Write the code to connect to the Network and print the IP address:
WiFi.begin(ssid, password);
Serial.println("Connecting to WiFi");
while (WiFi.status() != WL_CONNECTED) {
delay(500);
Serial.print(".");
}
Serial.println();
// Print ESP8266 Local IP Address
Serial.println(WiFi.localIP());
Lastly, you need to copy the code below. It serves the purpose of handling the web:
server.on("/", HTTP_GET, [](AsyncWebServerRequest *request){
request->send_P(200, "text/html", index_html, processor);
});
server.on("/temperaturec", HTTP_GET, [](AsyncWebServerRequest *request){
request->send_P(200, "text/plain", readDSTemperatureC().c_str());
});
server.on("/temperaturef", HTTP_GET, [](AsyncWebServerRequest *request){
request->send_P(200, "text/plain", readDSTemperatureF().c_str());
});
When we make a request on the root URL, we send the HTML text that is stored in the index_html variable. We also need to pass the processor function, that will replace all the placeholders with the right values.
server.on("/", HTTP_GET, [](AsyncWebServerRequest *request){
request->send_P(200, "text/html", index_html, processor);
});
We need to add two additional handlers to update the temperature readings. When we receive a request on the /temperaturec URL, we simply need to send the updated temperature value. It is plain text, and it should be sent as a char, so, we use the c_str() method.
server.on("/temperaturec", HTTP_GET, [](AsyncWebServerRequest *request){
request->send_P(200, "text/plain", readDSTemperatureC().c_str());
});
The same process is repeated for the temperature in Fahrenheit.
server.on("/temperaturef", HTTP_GET, [](AsyncWebServerRequest *request){
request->send_P(200, "text/plain", readDSTemperatureF().c_str());
});
Lastly, we can start the server.
server.begin();
The loop function is left empty as this is an asynchronous web server:
The final code will look as follows:
// Import required libraries
#ifdef ESP32
#include <WiFi.h>
#include <ESPAsyncWebServer.h>
#else
#include <Arduino.h>
#include <ESP8266WiFi.h>
#include <Hash.h>
#include <ESPAsyncTCP.h>
#include <ESPAsyncWebServer.h>
#endif
#include <OneWire.h>
#include <DallasTemperature.h>
// Data wire is connected to GPIO 4
#define ONE_WIRE_BUS 4
// Setup a oneWire instance to communicate with any OneWire devices
OneWire oneWire(ONE_WIRE_BUS);
// Pass our oneWire reference to Dallas Temperature sensor
DallasTemperature sensors(&oneWire);
// Replace with your network credentials
const char* ssid = "REPLACE_WITH_YOUR_SSID";
const char* password = "REPLACE_WITH_YOUR_PASSWORD";
// Create AsyncWebServer object on port 80
AsyncWebServer server(80);
String readDSTemperatureC() {
// Call sensors.requestTemperatures() to issue a global temperature and Requests to all devices on the bus
sensors.requestTemperatures();
float tempC = sensors.getTempCByIndex(0);
if(tempC == -127.00) {
Serial.println("Failed to read from DS18B20 sensor");
return "--";
} else {
Serial.print("Temperature Celsius: ");
Serial.println(tempC);
}
return String(tempC);
}
String readDSTemperatureF() {
// Call sensors.requestTemperatures() to issue a global temperature and Requests to all devices on the bus
sensors.requestTemperatures();
float tempF = sensors.getTempFByIndex(0);
if(int(tempF) == -196){
Serial.println("Failed to read from DS18B20 sensor");
return "--";
} else {
Serial.print("Temperature Fahrenheit: ");
Serial.println(tempF);
}
return String(tempF);
}
const char index_html[] PROGMEM = R"rawliteral(
<!DOCTYPE HTML><html>
<head>
<meta name="viewport" content="width=device-width, initial-scale=1">
<link rel="stylesheet" href="https://use.fontawesome.com/releases/v5.7.2/css/all.css" integrity="sha384-fnmOCqbTlWIlj8LyTjo7mOUStjsKC4pOpQbqyi7RrhN7udi9RwhKkMHpvLbHG9Sr" crossorigin="anonymous">
<style>
html {
font-family: Arial;
display: inline-block;
margin: 0px auto;
text-align: center;
}
h2 { font-size: 3.0rem; }
p { font-size: 3.0rem; }
.units { font-size: 1.2rem; }
.ds-labels{
font-size: 1.5rem;
vertical-align:middle;
padding-bottom: 15px;
}
</style>
</head>
<body>
<h2>ESP DS18B20 Server</h2>
<p>
<i class="fas fa-thermometer-half" style="color:#059e8a;"></i>
<span class="ds-labels">Temperature Celsius</span>
<span id="temperaturec">%TEMPERATUREC%</span>
<sup class="units">°C</sup>
</p>
<p>
<i class="fas fa-thermometer-half" style="color:#059e8a;"></i>
<span class="ds-labels">Temperature Fahrenheit</span>
<span id="temperaturef">%TEMPERATUREF%</span>
<sup class="units">°F</sup>
</p>
</body>
<script>
setInterval(function ( ) {
var xhttp = new XMLHttpRequest();
xhttp.onreadystatechange = function() {
if (this.readyState == 4 && this.status == 200) {
document.getElementById("temperaturec").innerHTML = this.responseText;
}
};
xhttp.open("GET", "/temperaturec", true);
xhttp.send();
}, 10000) ;
setInterval(function ( ) {
var xhttp = new XMLHttpRequest();
xhttp.onreadystatechange = function() {
if (this.readyState == 4 && this.status == 200) {
document.getElementById("temperaturef").innerHTML = this.responseText;
}
};
xhttp.open("GET", "/temperaturef", true);
xhttp.send();
}, 10000) ;
</script>
</html>)rawliteral";
// Replaces placeholder with DHT values
String processor(const String& var){
//Serial.println(var);
if(var == "TEMPERATUREC"){
return readDSTemperatureC();
}
else if(var == "TEMPERATUREF"){
return readDSTemperatureF();
}
return String();
}
void setup(){
// Serial port for debugging purposes
Serial.begin(115200);
Serial.println();
// Start up the DS18B20 library
sensors.begin();
// Connect to Wi-Fi
WiFi.begin(ssid, password);
Serial.println("Connecting to WiFi");
while (WiFi.status() != WL_CONNECTED) {
delay(500);
Serial.print(".");
}
Serial.println();
// Print ESP Local IP Address
Serial.println(WiFi.localIP());
// Route for root / web page
server.on("/", HTTP_GET, [](AsyncWebServerRequest *request){
request->send_P(200, "text/html", index_html, processor);
});
server.on("/temperaturec", HTTP_GET, [](AsyncWebServerRequest *request){
request->send_P(200, "text/plain", readDSTemperatureC().c_str());
});
server.on("/temperaturef", HTTP_GET, [](AsyncWebServerRequest *request){
request->send_P(200, "text/plain", readDSTemperatureF().c_str());
});
// Start server
server.begin();
}
void loop(){
}
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