[time-nuts] Got 60HZ?

[John Miles]

> 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
>  H__L__H__L__H__L
>
> 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.

True -- it's a common technique in synthesizers.

> 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.

The LPro-101 manual offers some advice of uneven quality on that subject,
but I think you'd be fine with either a two-transistor differential amp
(http://www.wenzel.com/documents/waveform.html) or a 74AC-series gate
(http://www.ke5fx.com/ac.htm).  See the other thread on reference-oscillator
input circuits as well.

-- john, KE5FX