I recently worked on a similar project, but wanted to create a 50 Hz output to be able torun a Mostek MK50250 clock chip in 24-hr/50Hz mode. I also wanted the stability of acrystal to avoid the daily variations of the local AC power source frequency. I could easily have created 50 Hz from an accurate reference source, but I wanted to havea separate circuit which could run on a battery during power outages and in case of loss ofthe reference source. To be accurate to one second in a 24-hour period the oscillator only has to be accurate to1 part in 86400, which is available in a relatively inexpensive 14-pin can type. If you picka convenient multiple of 60 Hz it is a simple matter to put together a divider chain. For anexample, you could use a 12 MHz oscillator with the C8051 board you mention to get120 Hz, then divide by 2 to get 60 Hz for your clock. For long-term accuracy you could then divide the 60 Hz and compare it to your masterreference every second, 10 seconds, 100 seconds, etc. until you reach an error count ofplus or minus one count, then add or subtract one count from your clock oscillatordivider. If you choose an oscillator that is slightly high in frequency, you would only have to subtractpulses every so often, which should be fairly simple to do. This method is very similar to the old Master/Slave mechanical clocks, where the slaveclocks ran fast by a few seconds per day. They were then stopped at midnight until theywere started again by a pulse from the master clock when it reached 00:00:00. -- Flemming Larsen --- Den ons 8/12/10 skrev Michael Poulos <[email protected]>:
Fra: Michael Poulos <[email protected]> Emne: [time-nuts] Got 60HZ? Til: "Discussion of precise time and frequency measurement" <[email protected]> Dato: onsdag 8. december 2010 20.13 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. 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. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
