In message <961218104807_1087348080@emout20.mail.aol.com>, "Mark A. Corio" writ
es:
>I have some sensitive analog circuitry that I need to do some relay switching


>return path.  Remember, I am very noise sensitive here.  In my current
>application the relay (reed or otherwise) will have the coil driven by a
>signal from another board (both ends of coil) without electrical connection
>the board with the signal.  Are reed relays more sensitive to coupling of
>noise to the signal from the coil since the contacts are surrounded by the
>actuating magnetic fields?  Any experiences with this are of most interest.

        I have mixed feelings about reed relays.
They are relatively quiet both electrically and mechanically, but they
are fragile and shock-sensitive.  While I don't know all of the constraints
imposed by the design, the first thing that comes to mind is to use a
CD4066 or even a CD4016 quad bilateral switch to do the audio switching.
Each gate on the chip is a pair of FET's which, when turned on, conduct
AC as long as the peeks don't exceed +- V(ss).  The DC control signals do not
appear in the audio path and the switching is clean and click-free.

        One could use an opto isolator to totally isolate the switching
board from the audio board.

        This is just a thought.  What say the rest?

Martin McCormick WB5AGZ  Stillwater, OK 36.7N97.4W
OSU Center for Computing and Information Services Data Communications Group