On Sun, Dec 31, 2006 at 10:33:24AM +0000, Dieter wrote:
> > Note that most things handle 5v signal levels well enough, although
> > we'll need something on any input signals to deal with 12v inputs.
>
> IIRC, the RS-232 spec is 5-15V, so you'd want to handle 15V in.
> And if possible, some protection from getting zapped by static would be good.
Nominally, +/-12V, but yes, it can exceed that.
I usually do the overvoltage protection on the inputs by adding a
series input resistance, and relying on the IC's internal input diodes to
clamp the pin to the voltage rails. The resistor limits the peak current
and protects the diodes. Then I put a large transient voltage suppressor
diode from each 12V rail to chassis ground. I protect the output pins with
large Schottky diodes to clamp it to each rail, and use a much smaller
series resistor, because of the cable capacitance an output must drive.
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