> R1 R2 Potential Divider at all the sources and switch the low voltage?


Yes, that's the immediate "solution" that comes to mind.
Unless keeping a resistor string always energised for each input is
unacceptable then this removes all high voltage switching.

Reed lifetime is dependent on switching current, and gets very high
[tm] as current approaches zero.
Here is an excellent Meder summary of lifetimes of their products at
different currents.
Some of their models achieve 1E9 cycles at < 10 mA,. others are in the
E8-E9 range.

             http://www.digikey.com/Web%20Export/Supplier%20Content/Meder_3=
74/PDF/MEDER_Reed-switch_Life_Test_Data.pdf

You'd want to ensure there was no significant capacitive component of
the divider string as at those voltages it would be easy to get short
but damaging current pulses as capacitance charges.

Meder technical papers here

              http://www.meder.com/technical-documents4.html

We use a reed switch in the Mini light. As long as they are handled
correctly during installation they stand up incredibly well to impact
forces - far better than spec sheet figures would suggest. I don't
think I've seen a redd failure in ? tens of thousands of lights
PROVIDED THAT they were handled and installed correctly. Break the
rules and you break the switch - not always visibly. I saw a few
broken ones at first with mis-handling the cause.








               Russell McMahon
--=20
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