FTDI_simple_alarm/alert.sh

#!/bin/bash
 if [ "$#" -eq  "0" ]
   then
    pid=$(pgrep -f alert.sh)
    kill $pid
 else
     while :
        do
            echo -ne 'FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF' > /dev/ttyUSB0
            sleep 1
        done
 fi