ServerHTTP.ino

#include "WiFi.h"
#include "ESPAsyncWebServer.h"

#define WIFI_SSID "<ssid>"
#define WIFI_PASSWORD "<password>"

// ---------------------------------------------------------------

// LM35 temperature sensor is connected to GPIO 33 (Analog ADC1_5)
const int lm35InputPin = 33;

const int esp32BitsPrecision = 10;

const float esp32MaxVolts = 1.5;

// ---------------------------------------------------------------

float analog_to_volts(float value, float max_volts, int n_bits) {
    // compute analog resolution
    float resolution = pow(2, n_bits) - 1;

    // transform value in [0, 2^n_bits] interval, to [0, max_volts] interval
    float volts = (value / resolution) * max_volts;

    return volts;
}

float volts_to_celcius(float volts) {
    // for LM35: divide by 10 mV (i.e., multiply by 100)
    return 100.0 * volts;
}

float analog_to_celcius(float value) {
    // converts analog value to volts
    float volts = analog_to_volts(value, esp32MaxVolts, esp32BitsPrecision);

    // converts volts value to celcius
    float celcius = volts_to_celcius(volts);

    return celcius;
}

float celcius_to_farenheit(float celcius) {
    float fahrenheit;

    /* celsius to fahrenheit conversion formula */
    fahrenheit = (celcius * 9 / 5) + 32;

    return fahrenheit;
}

float get_lm35_temperature() {
    // read analog value from input GPIO
    int analog_value = analogRead(lm35InputPin);

    // convert analog input to temperature (in celcius)
    float t_celcius = analog_to_celcius(analog_value);

    return t_celcius;
}

// ---------------------------------------------------------------

AsyncWebServer server(80);

// this sets the ground pin to LOW and the input voltage pin to high
void setup() {
    // using 9600 baud rate
    Serial.begin(9600);

    WiFi.begin(WIFI_SSID, WIFI_PASSWORD);
    while (WiFi.status() != WL_CONNECTED) {
        delay(1000);
        Serial.println("Connecting to WiFi..");
    }

    Serial.println(WiFi.localIP());

    server.on("/", HTTP_GET, [](AsyncWebServerRequest *request) {
        // get current LM35 temperature
        float t_celcius = get_lm35_temperature();
        float t_farenheit = celcius_to_farenheit(t_celcius);

        Serial.print(t_celcius);
        Serial.println(" C");
        Serial.println("");

        // formatting the json content to be sent
        char json_content[100];
        sprintf(
            json_content,
            "{ msg: 'The current temperature is %.2f celcius degrees'}\r\n",
            t_celcius
        );

        request->send(200, "text/plain", json_content);
    });

    server.begin();
}

// ---------------------------------------------------------------

// main loop
void loop() {}