Late to this thread, so apologies if it's been brought up already... but ad=
ding hysteresis to the logic level thresholds is a great way to boost noise=
 immunity. Using a Schmitt trigger like CD40106 or 74HC14 etc from memory g=
ives something like +Vth of 2/3 of Vdd and -Vth of 1/3 of Vdd... effectivel=
y means noise of up to 1/3 Vdd in amplitude can be rejected.
--=20
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