从php文件执行脚本

I have a php file which is called by a website:

example: serial_tx.php?v=W100

Within the php I write a log file where I can see which string v I received (W100 in this case).

The webserver is hosted on a Raspberry Pi and should send this data to the uart.

The files locations:

/SCRIPTS/serial_tx.php
/SCRIPTS/c/jmsend/serial_tx  // the executable, compiled from a C script

If I am in the root of the webserver and, from the console of my Pi, I run

sudo /var/www/html/SCRIPTS/c/jmsend/serial_tx W100

I get the command sent correctly.

With the php file I tried with system, shell_exec and exec without success.

shell_exec("sudo /var/www/html/SCRIPTS/c/jmsend/serial_tx ".$ric);

$ric is the received command. I tried with different path settings too (starting from Pi root or webserver root). All the files have a 777 as permissions.