On Wed, 12 Nov 1997 10:41:44 -0500 Pierce Nichols <pn30@COLUMBIA.EDU>
writes:
>On Wed, 12 Nov 1997, : Cassie Carstens wrote:
>
>> Short of using screen cable for every sensor, is there other devices
>> or goodies that can protect alarm systems from this assult????
>
>        Ouch... hrm... you could connect the sensors through
>opto-isolators (to protect the core) and then rig up a detection
>circuit
>that sets off the alarm if this happens.
>

        How about putting a pull-up resistor on the sensor, then running
the "pulled-up" sensor through a relatively high value resistor to the
PIC input.  The high value resistor should limit the current through the
PIC input clamp diodes while normal voltages can still pull the high
impedance input up or down.
        I've done this on status monitoring equipment at TV and radio
stations (similar resistor network driving HC devices) and have not yet
lost any parts with lotsa lightning around.


Harold