[time-nuts] Got 60HZ?
bill at iaxs.net
Sat Dec 11 18:29:35 UTC 2010
The original question referred to a good squaring chip. Then
we veered off into other ways to coax chips into delivering
60 Hz from 10 MHz. At the time, I thought there must be a way
to buy European 50 Hz synchronous clocks, or digital clocks
that use the line frequency.
Here's an electromechanical solution.
You'll need a small low voltage DC motor with good bearings,
a disk that fits on the motor shaft that has been drilled or
etched with two concentric circles of tiny holes, two light
source and detector pairs to get pulses from the holes, PLL
circuitry, and an amplifier to drive the motor.
One circle of holes generates a frequency that can be phase
locked to a standard your choice. The other circle generates
a frequency that is a binary multiple of 60 Hz. 120 Hz is
enough for a square wave output. A higher frequency is
required to approximate a sine wave.
For extra credit, add a copper disk to the motor shaft. Make
one or more electromagnets so that the copper disk passes
through the gap. Run the DC motor from a regulated voltage
that makes the frequencies about 1% high. Arrange the PLL to
drive the electromagnets to regulate the motor speed using
the counter field generated in the copper disk. See if the
copper disk can be made thin enough to also have the circles
In return for some mechanical skills, you can avoid strange
chips and arduous programming.
From: Michael Poulos
Sent: Wednesday, December 08, 2010 10:14 PM
To: Discussion of precise time and frequency measurement
Subject: [time-nuts] Got 60HZ?
Recently I bought a Efratom Ru frequency standard from eBay and a
frequency divider chip that makes 1MHZ,100KHZ,25KHZ,10KHZ,100HZ and a
1HZ output. Today I thought of a way to make a nice 60HZ so you can use
a mains-powered clock for the display (using amplifier and transformer
wired "backwards"). But, now you'll need 60HZ. A European has it easy
with 50HZ as you use a BASIC Stamp or Arduino to divide the 100HZ
output. But for 60HZ I came up with a solution:
You set up the Arduino to take the 10KHZ from the divider chip and
program it to count off 83 pulses to flip an output. But wait! Unless
you add a "leap count" every 3 flips of the output, it'll run fast.
Assume at the start the Arduino output starts high then turns low:
(83+83+84+83+83+84)*20 = 10,000 pulses = one second
Every output cycle and a half the voltage swing is a little over 1
percent longer because of the leap count. This means that the distortion
adds a slight inaccuracy, not enough to upset New Year's revelers. But
if you want a better 60HZ, try using the 100KHZ:
(833+833+834+833+833+834)*20 = one second
You see where this is going with leap counts. The ultimate of course is
one really good Arduino and (after a hex inverter to amplify it) take
the straight 10MHZ and apply this leap count technique:
(83333+83333+83334+83333+83333+83334)*20 = one really accurately made
60HZ = one nice second, just the thing for a Nixie clock. :)
Now, what is a good hex inverter to take the 10 million HZ of my
rubidiom movement to feed a frequency divider chip (and later Arduino)?
It needs to take the .5 of a volt sinewave and squarewave it and in a
normal 14 pin DIP (breadboardable) package.
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