Hi Oleg,

I think you can think of DTMF or FSK. If you are interested we can discuss the details with Gurus. In a recent project for security at 07 different floors of a Plaza, I have used the common telephone line and DTMF decoder.

Though it was manual that you have to dial the password of the slave from the master unit to engage a particular slave to log in, but it can be implemented in a customized way also.


Simon