[time-nuts] Building a mains frequency monitor

[jimlux]

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.