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Thread: HARSH ENVIRONMENT PIC
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face BY : Dennis Plunkett email (remove spam text)



At 20:32 25/10/99 -0700, you wrote:


Now all you ahve to do is protect the OPTOS!


How about this:-

switch common 0V
switch contact intp the base of a NPN transistor pulled high via 1k and a
series reisitor into the base of 10K.
Use schotkey diode clamps on the input lines.
Use current limit potection resistors on both lines say 100R
USe the tansistor as an active low switch.

This method is used in vehicle environments, agreed that there will be no
110VAC around, but lots of other stuff.

Oh yes, add some ferrite beads to the lines


Dennis



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