On Sat, Jul 14, 2012 at 06:15:14AM -0700, J. Forster wrote:
> I don't see why school crossing signs, water sprinklers, street or outdoor
> lighting need 1 second timing. Ten minutes, or a photocell, would be more
> than adequate.
While there are many many other applications, the issue for most
of these devices is not 1 second accuracy, but automagic setting of the
time without operator intervention or manual procedure required. For
many ordinary folks the always slightly different push button gyrations
required to set the time on a device with limited buttons and display
are all too often a complete barrier to getting the time set right (this
is the VCR "blinking 12:00AM" phenomenon). And in outside environments
clock oscillator thermal behavior will ensure something preset to the
correct will wander pretty far out quite quickly (plus of course DST
needs to be set too). And working with only approximate time is
another source of terrible confusion for users... if they set it to go
off at exactly 11 PM and it goes off at 11:08 PM they are likely going
to be confused and frustrated... especially if difficult or even
impossible steps are required to correct the time.
Photocells don't work for situations where the desired on or off
times are civil times (not turning on the water sprinklers until 11 PM
for example or turning off the tennis court lights at 10 PM)... at best
it takes lots of software to convert light and dark from them to
anything approximating a 10 minute accurate estimate of the time of day
and shadows and sun angles and so forth ensure that this is never going
to be particularly accurate.
> Synchronized traffic lights, perhaps. But there are other cheaper, ways of
> doing that like a simple radio link.
I refuse to believe that a reliable mile or more range RF
link would be cheaper than a loopstick and maybe a couple of passives
tied to pins on a SOC chip... and there are all those situations
where even a mile isn't enough or obstacles or RFI block ISM band
links.
--
Dave Emery N1PRE/AE, d...@dieconsulting.com DIE Consulting, Weston, Mass
02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in
celebration of what could have been, but wasn't and is not to be now either."
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