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Arduino and Fe-5680A?

Former Member

how would I use a Fe-5680A Rb frequency standard  with a arduino for a 10 digit clock as the last four digit's would be the milliseconds, and also would it be better to use a Fe-5680A Rb frequency standard rather than relying on a internal clock for a more percise time? for more info on the Fe-5680A Rb frequency standard here is a link to a pdf file and the last one is the one I would be using,(on page 11)http://freqelec.com/pdf/rfs_12pg.pdf ,  pin 3 is the lock signal and pin 7 is the MHz out. also I'm gussing I'll need to use a real time clock chip, but would it be possiable to have the Milliseconds, if so how would I use all these together to acheive a more than average accurate clock? Also if anyone wants to know I'll be using 10 VFD tubes for the display and I say it will be most likly a good idea to use multiplexing, cause you know who would really want to direct drive 10 7-segment VFD  tubes.

  • 0

    Have you read https://en.wikipedia.org/wiki/Atomic_clock? The reason I ask is you say you need milliseconds time in four digits when we are talking 1/1000 of a second which runs only 0-999. These atomic clocks are meant for GPS (which relies on time difference) and not time measurements. If you want to display a time in milliseconds, why not use Arduino itself? https://www.arduino.cc/en/Tutorial/SecretsOfArduinoPWM. The only requirement is to set the time, which can be done using NTP from the internet which will be needed with the FE-5680A or an RTC chip also. The FE-5680A will drift less than the RTC chip or Arduino that is all. The reset is needed less often for FE-5680A versus other means, unless this will be off the net for years!

    C

  • 0 in reply to clem57

    I just like a even number of 10 instead of 9, so the 7th digit will be just changing from 0 and 1 pretty fast so I'm aware that 1/1000  of a second only is 0-999, and yes I've read on the atomic clock, and I know there ment for GPS, I just wondered if it's possiable to integrate something like that, but if I can just simply and have the arduino do it, then I'll do that, so exactly how would I get the arduino to out put the milliseconds as well?

     

    do something like a loop with like a x++

     

    adding 1 to x every 1/1000

     

    if >= 999

    then

     

    x == 0?

     

    or something of the like? as isn't the millisecond command for the total amount of time that the arduino has been powered in milliseconds

  • 0 in reply to Former Member

    Oh, then we need a little math. The device using option 1 by default has a cycle time of 50.255055 Mhz. The Arduino (20mhz is the published max spec for the 328 chip) is slower.

    So, to use you need to build an external circuit to count/divide the clock into bigger segment say 1 Khz (your 1/1000 seconds) and interrupt the Arduino to do the math of actually time display on the tubes.

    50,255 times gives roughly 1 Khz.

    C

  • 0 in reply to clem57

    what part's would you recommand best to build this external count/divide circuit , also would I use a  Frequency divider, or am I just missing the point all together, xD

  • 0 in reply to Former Member

    Hi Stephen,

     

    The milliseconds and tens of milliseconds will be a blur, but may be useful to display if you intend to have some sort of stopwatch capability (e.g. timing a sports event down to the millisecond).

    I'm not sure what nixie tubes will display at that speed (I've never used such a display). They may appear dimly lit perhaps. You'd need to do a test.

     

    To do what you're aiming to do, as Clem mentioned, you could interrupt the microcontroller at (say) 1/1000 of a second using your accurate clock source. As a slight modification, just clock your microcontroller at

    a multiple of 1000 times a second (e.g. 16MHz) (i.e. remove the Arduino's crystal) and then implement in your software using any integrated clock/counter inside the Arduino for example, because the

    integrated clock/counter will also have interrupt capability.

    Here is an example (this is just an approximation - I've not used an ATmega chip in years, so the memory is vague):

     

    1. Divide your precision reference so that it is 16MHz

    2. Set your system clock prescaler in the ATmega chip to divide-by-1

    3. Set the 16-bit timer prescaler to divide-by-1

    4. Set a time counter variable tcount to zero. This tcount variable will represent thousandths of seconds.

    5. Set a 16-bit unsigned integer compare variable compare_val to (16e6/1000), i.e. 16000

    6. Set the 'output compare' register to compare_val, (i.e. initially 16000), and enable output compare match interrupt

     

    7. Upon the interrupt occurring, increment tcount by 1 and update your display.

    8. Increment compare_val by 16000 and re-enable the interrupt.

     

    Personally I think it would be better to get the Arduino running using the existing crystal and add your Nixies etc., until you're happy with your code and the result, and then remove the crystal and replace with the

    precision 16MHz reference.

  • 0 in reply to shabaz

    of course I'll do it with a internal existing crystal first, and have it all working properly first, also there is a difference between nixie tubes, and VFD tubes, nixie tubes require more power to heat up each filiment digit to glow, and it has a gas in them(which are cool too, but harder to use), and VFD tubes was what was used before LCD's replaced them, there vacuum fluorescent display, so they work much like a vacuum tube as they have little to no gas in them, they work in a way a crt works, except they require less voltage than nixie's(and crt's) since nothing is suppose to heat up and glow hot, which is 50v-60v for VFD tubes. also thank you very much on this detailed explaination, I really apreciate it, this helps me a ton.