[time-nuts] Clocking a PIC16F628A from a Rubidium Standard

Chuck Harris cfharris at erols.com
Mon Nov 28 17:45:22 UTC 2011


David VanHorn wrote:
>
>
> Somewhere or another there should be a compromise that makes you happy... you
> will, however, never achieve true safety as long as you are alive.
>
>
> I am far more aware of this than you might suspect, but I do think that it is a
> very good idea to know the risks involved. An optoisolator is vanishingly unlikely
> to fail shorted, in that they are specifically designed with this failure mode in
> mind. A resistor is likely to fail open, but failing shorted isn't unheard of.
> See also designs for wrist straps.
>
> I won't be trusting a single resistor to sit between me and a fire that could kill
> people.

Trust me, if you use any plug in consumer grade electronics, you already are.
Compact fluorescent bulbs are a particularly egregious example.

By the way, for every 1M resistor type I am aware of, failing short
circuit is essentially impossible.  It could happen if the resistor is
mounted with both ends in physical contact with a pcb trace, but that
is a bad mechanical design that would compromise an optoisolator too.

-Chuck Harris




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