Using HTML Drop-down Select Boxes for Hour and Minute on Arduino Web Server

An Arduino and Ethernet shield with SD card are used as a web server to host a page that allows a user to select hour and minute values from two HTML drop-down select boxes. The time sent to the Arduino can be used to set a real-time clock from a web page or for other time related purposes.

To demonstrate that the Arduino is getting the time values from the web page, they are displayed in the Serial Monitor window of the Arduino IDE. JavaScript in the hosted HTML web page is used to send the hour and minute time values to the Arduino periodically. This allows the code to easily be integrated with the Arduino Ajax web server code. The code could also be adapted to send the time only when a button is clicked.

This video shows the sketch running and the selected time values from the web page being sent to the Serial Monitor window:


Web Server Hardware

An Arduino Uno, Ethernet shield and 2GB micro SD card were used for testing the code. Any Arduino board that is compatible with the Ethernet shield should work.

Setting up the Web Server

The Arduino sketch below must be loaded to the Arduino with Ethernet shield. The HTML web page from below must be copied to a file called index.htm on the micro SD card. Insert the micro SD card into the socket on the Ethernet shield.

Arduino Web Server Sketch

Copy this code and paste it to the Arduino IDE for loading to the Arduino board with Ethernet shield and SD card. Change the MAC and IP address to suit your own system.

  Program:      drop_down_select

  Description:  Arduino web server that gets hour and
                minute from two drop-down select boxes on an
                HTML page.
                The web page is stored on the micro SD card.
  Date:         22 June 2015
  Author:       W.A. Smith,

#include <SPI.h>
#include <Ethernet.h>
#include <SD.h>
// size of buffer used to capture HTTP requests
#define REQ_BUF_SZ   60

// MAC address from Ethernet shield sticker under board
byte mac[] = { 0xDE, 0xAD, 0xBE, 0xEF, 0xFE, 0xED };
IPAddress ip(192, 168, 0, 20); // IP address, may need to change depending on network
EthernetServer server(80);  // create a server at port 80
File webFile;               // the web page file on the SD card
char HTTP_req[REQ_BUF_SZ] = {0}; // buffered HTTP request stored as null terminated string
char req_index = 0;              // index into HTTP_req buffer

void setup()
    // disable Ethernet chip
    pinMode(10, OUTPUT);
    digitalWrite(10, HIGH);
    Serial.begin(115200);       // for debugging
    // initialize SD card
    Serial.println("Initializing SD card...");
    if (!SD.begin(4)) {
        Serial.println("ERROR - SD card initialization failed!");
        return;    // init failed
    Serial.println("SUCCESS - SD card initialized.");
    // check for index.htm file
    if (!SD.exists("index.htm")) {
        Serial.println("ERROR - Can't find index.htm file!");
        return;  // can't find index file
    Serial.println("SUCCESS - Found index.htm file.");
    Ethernet.begin(mac, ip);  // initialize Ethernet device
    server.begin();           // start to listen for clients

void loop()
    byte hour;
    byte minute;
    EthernetClient client = server.available();  // try to get client

    if (client) {  // got client?
        boolean currentLineIsBlank = true;
        while (client.connected()) {
            if (client.available()) {   // client data available to read
                char c =; // read 1 byte (character) from client
                // limit the size of the stored received HTTP request
                // buffer first part of HTTP request in HTTP_req array (string)
                // leave last element in array as 0 to null terminate string (REQ_BUF_SZ - 1)
                if (req_index < (REQ_BUF_SZ - 1)) {
                    HTTP_req[req_index] = c;          // save HTTP request character
                // last line of client request is blank and ends with \n
                // respond to client only after last line received
                if (c == '\n' && currentLineIsBlank) {
                    // send a standard http response header
                    client.println("HTTP/1.1 200 OK");
                    // remainder of header follows below, depending on if
                    // web page or XML page is requested
                    // Ajax request - send XML file
                    if (StrContains(HTTP_req, "ajax_inputs")) {
                        // send rest of HTTP header
                        client.println("Content-Type: text/xml");
                        client.println("Connection: keep-alive");
                        // print the received hour and minute to the Serial Monitor window
                        // if received with the incoming HTTP GET string
                        if (GetTime(&hour, &minute)) {
                          Serial.print("Hour: ");
                          Serial.print("Minute: ");
                    else {  // web page request
                        // send rest of HTTP header
                        client.println("Content-Type: text/html");
                        client.println("Connection: keep-alive");
                        // send web page
                        webFile ="index.htm");        // open web page file
                        if (webFile) {
                            while(webFile.available()) {
                                client.write(; // send web page to client
                    // reset buffer index and all buffer elements to 0
                    req_index = 0;
                    StrClear(HTTP_req, REQ_BUF_SZ);
                // every line of text received from the client ends with \r\n
                if (c == '\n') {
                    // last character on line of received text
                    // starting new line with next character read
                    currentLineIsBlank = true;
                else if (c != '\r') {
                    // a text character was received from client
                    currentLineIsBlank = false;
            } // end if (client.available())
        } // end while (client.connected())
        delay(1);      // give the web browser time to receive the data
        client.stop(); // close the connection
    } // end if (client)

// extract hour and minute from the incoming HTTP GET data string
// returns true only if both the hour and minute have been received
boolean GetTime(byte *hr, byte *mn)
  boolean valid_time = false;  // hour and minute received flag
  char *str_part;              // pointer to part of the HTTP_req string
  char str_time[3] = {0};      // used to extract the times from HTTP_req string
  // get pointer to the beginning of hour data in string
  str_part = strstr(HTTP_req, "&h=");
  if (str_part != NULL) {
    // get the hour from the string
    str_time[0] = str_part[3];
    str_time[1] = str_part[4];
    *hr = atoi(str_time);
    // get pointer to the beginning of minute data in string
    str_part = strstr(HTTP_req, "&m=");
    if (str_part != NULL) {
      // get the minute from the string
      str_time[0] = str_part[3];
      str_time[1] = str_part[4];
      *mn = atoi(str_time);
      // got the hour and the minute
      valid_time = true;

  return valid_time;

// sets every element of str to 0 (clears array)
void StrClear(char *str, char length)
    for (int i = 0; i < length; i++) {
        str[i] = 0;

// searches for the string sfind in the string str
// returns 1 if string found
// returns 0 if string not found
char StrContains(char *str, char *sfind)
    char found = 0;
    char index = 0;
    char len;

    len = strlen(str);
    if (strlen(sfind) > len) {
        return 0;
    while (index < len) {
        if (str[index] == sfind[found]) {
            if (strlen(sfind) == found) {
                return 1;
        else {
            found = 0;

    return 0;

Arduino Hosted HTML Page

This code gets copied to the index.htm file on the micro SD card.

<!DOCTYPE html>
<html lang="en">
        <meta charset="utf-8">
        <title>Drop-Down Select Box Example</title>
        strHour = "";
        strMin = "";
        function GetArduinoIO()
            nocache = "&nocache=" + Math.random() * 1000000;
            var request = new XMLHttpRequest();
            // get the values from the drop-down select boxes
            var sel_hour = document.getElementById("selHour");
            if (sel_hour.selectedIndex > 0) {
                strHour = "&h=" + sel_hour.options[sel_hour.selectedIndex].text;
            else {
                // the first item in the drop-down box is invalid text, so clear the string
                strHour = "";
            var sel_min = document.getElementById("selMin");
            if (sel_min.selectedIndex > 0) {
                strMin = "&m=" + sel_min.options[sel_min.selectedIndex].text;
            else {
                strMin = "";

            // send HTTP GET request with LEDs to switch on/off if any
  "GET", "ajax_inputs" + strHour + strMin + nocache, true);
            setTimeout('GetArduinoIO()', 3000);

    <body onload="GetArduinoIO()">
        <select id="selHour">
            <option selected="selected" value="">Select Hour</option>
            <option value="00">00</option>
            <option value="01">01</option>
            <option value="02">02</option>
            <option value="03">03</option>
            <option value="04">04</option>
            <option value="05">05</option>
            <option value="06">06</option>
            <option value="07">07</option>
            <option value="08">08</option>
            <option value="09">09</option>
            <option value="10">10</option>
            <option value="11">11</option>
            <option value="12">12</option>
        <select id="selMin">
            <option selected="selected" value="">Select Minute</option>
            <option value="00">00</option>
            <option value="01">01</option>
            <option value="02">02</option>
            <option value="03">03</option>
            <option value="04">04</option>
            <option value="05">05</option>
            <option value="06">06</option>
            <option value="07">07</option>
            <option value="08">08</option>
            <option value="09">09</option>
            <option value="10">10</option>
            <option value="11">11</option>
            <option value="12">12</option>
            <option value="13">13</option>
            <option value="14">14</option>
            <option value="15">15</option>
            <option value="16">16</option>
            <option value="17">17</option>
            <option value="18">18</option>
            <option value="19">19</option>
            <option value="20">20</option>
            <option value="21">21</option>
            <option value="22">22</option>
            <option value="23">23</option>
            <option value="24">24</option>
            <option value="25">25</option>
            <option value="26">26</option>
            <option value="27">27</option>
            <option value="28">28</option>
            <option value="29">29</option>
            <option value="30">30</option>
            <option value="31">31</option>
            <option value="32">32</option>
            <option value="33">33</option>
            <option value="34">34</option>
            <option value="35">35</option>
            <option value="36">36</option>
            <option value="37">37</option>
            <option value="38">38</option>
            <option value="39">39</option>
            <option value="40">40</option>
            <option value="41">41</option>
            <option value="42">42</option>
            <option value="43">43</option>
            <option value="44">44</option>
            <option value="45">45</option>
            <option value="46">46</option>
            <option value="47">47</option>
            <option value="48">48</option>
            <option value="49">49</option>
            <option value="50">50</option>
            <option value="51">51</option>
            <option value="52">52</option>
            <option value="53">53</option>
            <option value="54">54</option>
            <option value="55">55</option>
            <option value="56">56</option>
            <option value="57">57</option>
            <option value="58">58</option>
            <option value="59">59</option>


Running the Web Server Drop-down Select Box Project

With the index.htm file on the SD card and the sketch loaded to the Arduino, open the Serial Monitor window and then use a web browser to surf to the IP address that is set in the sketch.

Change the hour and minute values in the drop-down boxes to valid time values to see the hour and minute displayed in the Serial Monitor window. Both the hour and minute must be set to valid values before anything is displayed.

5 thoughts on “Using HTML Drop-down Select Boxes for Hour and Minute on Arduino Web Server

  1. Hi,

    I have 2 questions.
    1) Currently, I have the setup similar to above. For example, once the time is selected on the webpage, it will send over to the arduino. When the time is up, the buzzer will sound.

    However , I noticed that if I power off the arduino and power on again, the buzzer will not sound when the time is up. Is there any way that the settings can be stored so that when the arduino is powered up, the settings remained?

    2) I have a save button on the webpage where the time will be saved via cookies and a recover button to read from cookies and populate the values ( dropdown list, checkbox). Currently, I’m able to save the cookies on a text file on the SD card. May I know what can be done so that when recover button is clicked, read from the text file and populate the values on the webpage?

  2. Hello,

    1) I used the above example and added a save and recover button. When save button is clicked, the values are saved in a text file. May I know how can the saved values be populated on the click of the recover button?

    2)I relized that once I power off the arduino, the settings set is gone. May I know how do I save an array into eeprom? Please advise if there are other methods for the values in the array to remain even when the arduino is powered off and on.

    Thanks in advance!

  3. Hi,

    Kindly advice after the values are selected via the dropdown box, how the values can be saved into the eeprom memory so that if the arduino get powered off and powered on again, the values will be remembered.

    Thanks in advance!

  4. Hii
    i would like to ask about the buffer of ethernet board
    how many combo box and text box i can add in the html web page
    is the sd server solve the problem of limitation in buffer size
    so i can add a lot of combo box and text box
    if no what the best solution ?

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