Re: Why is AC 60 Hz?



Just thought I'd throw this observation in:
I was recently breadboarding a counter/frequency divider chip using a
32.768KHz TTL oscillator source. The counter chip train was set to
divide by n multiples of 32768, (where n would be
switch-selectable)then roll over to 0 while the "carry out" pin on the
last chip in the train went from high to low for about one clock cycle
(~30.5 microseconds). I had an LED hooked up to the carry out pin. I
set it for 8 second intervals and powered it up. To my surprise, I
could "see" the 15 microsecond flicker every 8 seconds! Maybe more
like it should be worded as "perceive" than "see".
Got me to thinking: How low could I go on the pulse width and still
perceive the flicker? What if I put an inverter between carry out and
the LED, so that the LED transition would be from low to high?
But I was in a hurry to get the project done, so I didn't go any
further.
I'm sure this has been extensively studied, investigating all the
variables(light source, rest interval, light intensity, spectral
output, EEGs, age/sex/ethnic groups, etc. Anybody know of any studies
that have been done or refer me to a source?


On Sun, 15 May 2005 19:02:43 +0000 (UTC), don@xxxxxxxxxxxxxx (Don
Klipstein) wrote:

>In article <%Nphe.1351567$6l.1107625@pd7tw2no>, Dwayne wrote:
>>
>>Higher frequencies have higher loss.
>>You body has more resistance to higher frequencies.
>>You eyes can perceive light flicker at 40 Hertz.
>>You nerve system runs at ~40 Hertz.
>>
>>So low frequency is bad for lighting and electrocution. High frequencies are
>>bad for motors. Thus the compromise.
>
> Electrocution has nothing to do with choice of 50-60 Hz, since these
>frequencies are actually close to as bad as it gets for electrocution.
> The way I hear it, 50 and 60 Hz are good for motors. Otherwise the best
>frequency overall is higher.
>
> - Don Klipstein (don@xxxxxxxxx)

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