Hi again,

I have some sensitive analog circuitry that I need to do some relay switching
in for varying some filter bandwidths and other things.  I am considering
using reed relays.  Does anyone have any comments about this?  I would like
to drive the relay coils direct from a PIC I/O pin (16C74A or 16C84.....not
sure yet).  Will the protection diodes on the PIC I/O pins be adequate for
coil suppression or do I need external diodes as with other relay types?  I
have no experience with reed types but believe the inductive kick should be
smaller from reeds.

In the past, for this type of application I have used low signal level
latching relays so as not to have a constant current flowing through the
coils......I have had problems with noise on the coil drive signals being
imparted on the signal in standard type relays.  This approach also let me
use a common ground plane without the coil current causing problems in the
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.

Thanks again.

Mark A. Corio
Rochester MicroSystems, Inc.
200 Buell Road, Suite 9
Rochester, NY  14624
Tel:  (716) 328-5850 --- Fax:  (716) 328-1144
http://www.frontiernet.net/~rmi/

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