onclick místo onchange

<?php
define('BASE_DIR', dirname(__FILE__));
require_once(BASE_DIR.'/config.php');
$config = array();
$debugString = "";
$options_em = array( 'Auto' => 'auto', 'Night' => 'night' );
function initCamPos() {
$tr = fopen("pipan_bak.txt", "r");
if($tr){
while(($line = fgets($tr)) != false) {
$vals = explode(" ", $line);
echo '<script type="text/javascript">init_pt(',$vals[0],',',$vals[1],');</script>';
}
fclose($tr);
}
}
function makeOptions($options, $selKey) {
global $config;
switch ($selKey) {
case 'flip':
$cvalue = (($config['vflip'] == 'true') || ($config['vflip'] == 1) ? 2:0);
$cvalue += (($config['hflip'] == 'true') || ($config['hflip'] == 1) ? 1:0);
break;
case 'MP4Box':
$cvalue = $config[$selKey];
if ($cvalue == 'background') $cvalue = 2;
break;
default: $cvalue = $config[$selKey]; break;
}
if ($cvalue == 'false') $cvalue = 0;
else if ($cvalue == 'true') $cvalue = 1;
foreach($options as $name => $value) {
if ($cvalue != $value) {
$selected = '';
} else {
$selected = ' selected';
}
echo "<option value='$value'$selected>$name</option>";
}
}
?>

<tr>
<td><select onchange="send_cmd('em ' + this.value)"><?php makeOptions($options_em, 'exposure_mode'); ?></select></td>
</tr>

<form method="get" action="test.php">
<input type="submit" value="Posviť " name="on" > <----- sem "night"
<input type="submit" value="Zhasni" name="off" > <---- sem "auto"
</form>
<?php
$setmode17 = shell_exec("/usr/local/bin/gpio -g mode 24 out");
if(isset($_GET['on'])){
$gpio_on = shell_exec("/usr/local/bin/gpio -g write 24 1");
makeOptions('night');
echo "Svítí";
}
else if(isset($_GET['off'])){
$gpio_off = shell_exec("/usr/local/bin/gpio -g write 24 0");
makeOptions('auto');
echo "Nesvítí";