[time-nuts] Fwd: Home-brew GPSDO

Jim Harman j99harman at gmail.com
Thu Mar 17 16:09:40 EDT 2016


-- re-posting with smaller attachment --


On Thu, Mar 17, 2016 at 12:40 PM, Logan Cummings <logan.cummings at gmail.com>
wrote:

>  I was planning on using the Due's ADC to measure the voltage on the
> integrator capacitor, but hadn't decided yet about a "good" current source
> vs. a series resistor on the output of an XOR or DFF phase comparator to
> put charge on the capacitor.
>
>      Hopefully someone else can chime in with some better links and circuit
> descriptions.
>

You might want to consider the approach used in the attached schematic and
write-up. This is for an Arduino Micro based system, but you should be able
to adapt it to work with the Due. The simple RC network works OK if you can
set the ADC full scale range to 2.5 V or less, but shows some nonlinearity
at the high end due to the exponential charging. I have been experimenting
with a circuit that uses a better current source, which I can pass along if
you are interested. So far the performance seems to be about the same as
this simple circuit.


-- 

--Jim Harman




-- 

--Jim Harman
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