var jsonString = "";
function jsonconversion(){

        jsonString = JSON.stringify(myArr);
        return jsonString;
        console.log(jsonString);

        $.ajax({
       type: "POST",
       url: "http://192.168.192.17:80/watercooler/index2.php",
       data: jsonString,
       complete: function() {
            console.log("Success");
       },
       error: function() {
           console.log("Function: forward_to_server() error")
       }
    });
}

<?php

$servername = "localhost";
$username = "root";
$password = "xx";
$dbname = "xx";

//$myArray = $_REQUEST['jsonString'];
$myArray = array(100,1,19);

$con = mysqli_connect($servername,$username,$password ,$dbname) or die ("could not connect database");
echo $myArray;

$keys = array_keys($myArray);              // get the value of keys
$rows = array();                         // create a temporary storage for rows
foreach($keys as $key) {                 // loop through
    $value = $myArray[$key];               // get corresponding value
    $rows[] = "('" . $key . "', '" . $value . "')";
                                         // add a row to the temporary storage
}
$values = implode(",", $rows);           // 'glue' your rows into a query
$sql = "INSERT INTO php_test (temp, sound, light) VALUES (10,20,30)"; //. $values
$rs = mysqli_query($con,$sql) or die(mysqli_error($con));

if ($con->query($sql) === TRUE) {
    echo "New record created successfully";
} else {
    echo "Error: " . $sql . "<br>" . $con->error;
}

$con->close();

?>