I understand your point, Terry.. Which I think is the classic "Slippery
Slope" argument. You get used to cutting corners, before you know it
you're trying the same tricks at work where you design nuclear reactor
cooling systems, the systems fail due to your design choices that were
outside of specification, etc.
Luckily for me, I take mission criticality into account when I make a
design. A nixie clock project (for me) is foremost a fun chance to try
new things and sandbox some experimentation. Disclaimer: I don't sell my
clocks and I also don't use them in mission critical applications such
as drones or heart pumps. If something fails because of a design choice
that I made, then I make a note of it and change the experimental
design. The fact is that mission criticality is just another input in
the requirements phase of the design. Things like component count, size,
feature set, hazard analysis. Take the time to come up with some real
product requirements before you start drawing a schematic. Makes things
a lot easier.
-Adam W7QI
On 6/1/2012 8:09 AM, Terry S wrote:
The part is fabbed in HVCMOS, so yes, it will continue to function at
some level down to where the CMOS transistor structures no longer
switch -- probably well below 3 volts. But...
The problem with using a part like that outside its spec is that you
simply can't predict what parameters won't be met. What if it affects
set-up or hold times? What if it affects output drive or input
impedance? There are simply so many things that can go wrong --
internal timing conditions that might not be met. As a hobbyist, you
might be forgiving of a misbehavior if it doesn't manifest itself
visibly on your clock display, or you find a work around for a timing
problem -- but what if this were a life critical medical or industrial
application, or a mission critical military app? As an engineer or
designer, your butt would be on the line should you use a part outside
its specs and someone gets hurt or dies, or your drone crashes...
Speaking of drones, Obama is in town today, about 6 blocks from here,
speaking at Honeywell. I bet I can't even go out for lunch today
without running into his entourage. Gonna be another vending machine
lunch I guess.
Terry
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