On 4/9/16 10:20 PM, Bill Hawkins wrote:
The schematic is too simple. There is noise on the power line from
switching things on and off, leakage from dimmers and switching power
supplies, and the occasional animal that gets across the HV distribution
line, not to mention lightning, induced or direct.
A simple capacitor will reduce high frequency stuff. The purist will
invest in an L and C that resonates at 60 Hz.
Or a series of R/C stages: you don't care about loss.
Alternatively, use a
synchronous motor driving a load with sufficient inertia in combination
with a slotted disk and photo pickup. Perhaps an old record turntable
will do - but not one with a regulated DC motor.
A clever idea because of the mechanical low pass filtering, but probably
impractical..
A record turntable with a synchronous motor? That's going to be ancient
and hard to find in this age of digital music players. People like us
would happen to have something in the garage.. but for a science fair
project, unlikely that a 6-12th grader would have such a thing, or even
know where to find one. *I* have a lot of junk in the garage, and even
some synchronous motors, but not one that could directly be connected to
the mains.
an AC powered rotary dial electric clock, perhaps? (assuming it's not a
wall wart powering a "quartz movement".)
The science fair folks got enough interesting data without all that, but
the precision is not known.
The link didn't have any reference to code at all.
This is a way of looking at frequency variations with natural causes
that does not require expensive equipment, if done right.
I think that the key, especially for the putative science fair project,
if *I* were the judge in senior division, would be good software to look
for anomalies and excising oddball transients.
have a simple data logger that logs the time of zero crossings (or
similar), and then post process to reject zero crossings that aren't
within some "expected band" and which tolerates "missing pulses".
That would be a winning project. Assuming it weren't copied from
somewhere - and that's why they want people like us as judges.
The International Science and Engineering Fair is in May in Phoenix this
year, and they're always looking for judges. Always the week after
(U.S.) Mother's day.
https://student.societyforscience.org/grand-award-judges
Ignore the formal qualifications listing - if you have the chops and
experience, they'll take you.
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