Json export for google charts

<?php
$solartracker = "/home/pi/Documents/Projects/ArduinoSerialImport/solartracker.db";
$dsn = "sqlite:$solartracker";

try {
    $db = new PDO($dsn);
    $db->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
} catch (PDOException $error) {
    echo "Failed to connect to the database using DSN:<br>$dsn<br>";
    throw $error;
}

$stmt = $db->prepare("SELECT voltage, current, datestamp FROM stuffToPlot");
$stmt->execute();

$rows = array();
$table = array();

$table['cols'] = array(
    array('label' => 'Time', 'type' => 'date'),
    array('label' => 'Power', 'type' => 'number')
);

while ($row = $stmt->fetch(PDO::FETCH_ASSOC)) {
    $voltage[] = $row['voltage'];
        $current[] = $row['current'];

        $voltage = array();
        $current = array();


    $date1 = new DateTime();
    $date2 = "Date(".date_format($date1, 'Y').", ".((int) date_format($date1, 'm') - 1).", ".date_format($date1, 'd').", ".date_format($date1, 'H').", ".date_format($date1, 'i').", ".date_format($date1, 's').")";

    $power = array();
    foreach ($voltage as $key => $door){
             $power[] = $door * $current[$key];}


    $temp = array();
    $temp[] = array('v' => (float) $power);
    $temp[] = array ('v' => (string) $date2);
    $rows[] = array ('c' => $temp);

}

$table['rows'] = $rows;

echo json_encode($table);

$fp = fopen('data.json', 'w');
fwrite($fp, json_encode(array('cols' =>$table)));

fclose($fp);
?>