| Electronics > Projects, Designs, and Technical Stuff |
| Divide by 10000000 |
| (1/10) > >> |
| NivagSwerdna:
I bought a second hand Rb frequency reference that outputs a 10MHz sine What is the smallest/cheapest/simplest way to divide by 10M to get a 1PPS pulse? Thanks in advance |
| NivagSwerdna:
After a bit of googling... http://www.leapsecond.com/pic/picdiv.htm That's quite a sweet solution... and apparently it works with the sine rather than square clock. |
| Psi:
Ironically the cheapest way maybe a 50c mcu. Clock it from the 10mhz and setup a timer to toggle a pin at 1pps in hardware |
| bktemp:
--- Quote from: blueskull on May 31, 2017, 07:49:45 am ---It all depends what you want to do with 1pps. If it is only to drive an alarm clock, then it is fine to do that with a MCU. If you are actually going to feed it to a discipline clock generator which will use 1pps input to drive PLL in order to generate a perfectly phase aligned clock, then think twice. Your MCU is likely to generate quite some jitter that will ruin your output clock. That's why all GPS modules have 1pps output, but timing optimized GPS modules are so expensive -- the former generates 1pps for counting seconds, the latter generates 1pps for disciplining an oscillator, hence phase alignment (jitter) is crucial. --- End quote --- A typical microcontroller should not generate any jitter at all (except from some analogue jitter due to the clock input not being perfect) as long as you use a constant divider factor, because everything runs synchronous to the input clock. Small microcontrollers have a highly predictable diming, even when doing the division in software. As far as I know the 1pps signal on GPS modules is generated in software. Fast microcontrollers with cache don't have a very predictable interrupt latency, therefore the exact timing will vary slightly. |
| mikerj:
--- Quote from: blueskull on May 31, 2017, 07:49:45 am ---It all depends what you want to do with 1pps. If it is only to drive an alarm clock, then it is fine to do that with a MCU. If you are actually going to feed it to a discipline clock generator which will use 1pps input to drive PLL in order to generate a perfectly phase aligned clock, then think twice. Your MCU is likely to generate quite some jitter that will ruin your output clock. --- End quote --- If you are clocking the micro from the GPS 10MHz clock, and the division is performed by a timer rather then software, then you are only adding the residual jitter from the hardware timer. This isn't something you'd ever see specified in a datasheet, do you have any numbers? Disciplined clock sources perform a lot of averaging on the 1PPS signal anyway, so a small amount of jitter shouldn't be a problem. |
| Navigation |
| Message Index |
| Next page |