Update Packet Data Dynamically

Hello Sir,

$packet .= "\x04";
$packet .= "\x00\x00\x00";
$packet .= "\x00\x00\x00\x00";
$packet .= "\x00\x00\x00\x00";
$packet .= "\x19\x02\x01\x02\x01\x01\x00\x03"; // Serial Number

This is my sample code. At last of the code it represents the serial number of my device, to which i have to send my packet.

My problem is that, If there are number of devices and device have their unique serial number. So i want to send packet with that number. and for that i m just fetch the serial number from database and just convert that code into hexcode

Decimal Serial Number : 25 2 1 2 1 1 0 3
Hec Serial Number : 19 02 01 02 01 01 00 03

This hex serial number is stored into $SR_NO;
and when i m going to call this variable instead of manually enter, it is not work.

$packet .= "\x04";
$packet .= "\x00\x00\x00";
$packet .= "\x00\x00\x00\x00";
$packet .= "\x00\x00\x00\x00";
$packet .= "$SR_NO";

but if I fill it manually

$packet .= "\x04";
$packet .= "\x00\x00\x00";
$packet .= "\x00\x00\x00\x00";
$packet .= "\x00\x00\x00\x00";
$packet .= "\x19\x02\x01\x02\x01\x01\x00\x03"; // Serial Number

it will work.

According to my application it is necessary to pur serial number dynamically
So can you please suggest me that how can i resolve my problem ?

Thanks
(Kartik Patel)

Sounds like to me that however you're converting your serial number isn't returning what you're expecting. What I imagine may be happening is that your hex conversion function is converting to numbers/letters and not to ascii which is what you really need. To test, you could echo $SR_NO to the screen or webpage. If you see numbers and/or letters, then it's your number conversion process.