Need tutor to connect Parallax PIR using 20m cable

i just mail parallax about it , they tell me that i need line driver in order arduino to read the PIR signal
i'm wonder , how to make line driver , the distance between my PIR sensor and arduino is about 20m ,
and perhaps , somebody can help me design the multiplex system ? , need to control about 8 PIR sensor here

thanks

Jeff

i'm wonder , how to make line driver

You don't make them: you buy them.

You can use a chip made for RS-422 or RS-485, like the 75117 or 75179. That'll give you a reliable logic connection at the Arduino end that tracks the signal at the PIR.

There are examples of using multiplexers in the Playground area.