I use a bank of Clare CPC1016N
(http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail?name=CLA160-ND)
on a home-made PCB to great success. You can protect their inputs
with a simple zener to ground (and a resistor to keep the current in
the right range, check the data sheet). Tie one side of their outputs
to +3.3v and the other to your I/O. Just a few dollars and you're
good to go.
--- In "eric.robishaw" <> wrote:
>
> What kind of opto-isolation / voltage suppression circuitry or devices
> would you recommend for a 7800 DIO?
>
> I'll be reading outdoor field devices highly susceptible to voltage
> spikes potentially significantly > than the 5V toleration.
>
> I know I can spend $250 for a device from Phoenix Contact, but I need
> to go cheap (I know, you get what you pay for, but it doesn't make
> sense to pay the same amount for protection as I do for the board
itself).
>
> I'm looking for either a cheap DIN-rail device (~$50 for 4 inputs), or
> some simple circuitry I can put on my own PCB.
>
> Ideas?
>
> Thanks
> Eric
>
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