[time-nuts] Arduino Frequency Accuracy

[Dennis Ferguson]

On 18 Jan, 2014, at 20:11 , Jim Lux <jimlux at earthlink.net> wrote:
> Just in case you want to build a clock with an Arduino..
> 
> http://jorisvr.nl/arduino_frequency.html
> 
> ADEV measurements, etc.
> 
> 
> take home message.. absolute accuracy is a few kHz out of 16 MHz... probably a 100 ppm crystal.
> 
> On some Arduinos (or Teensy3's which is what I use) there's a provision for a 32kHz clock crystal.. that might be a bit better as a time base.

That's a sloppy crystal if what you are looking for is an oscillator
with an output frequency which is very close to the number written
on the crystal's package, but it might not be so bad if you measure
its frequency under actual operating conditions and use the
calibrated value instead.

I think the ADEV of the crystal is in fact rather good judged by PC
standards.  I interpret the floor of near 10^-9 at 100 seconds as
meaning some (mythical?) optimal synchronization software might
keep a clock based on that within 100 ns of the GPS receiver at
an adjustment rate of about one every 100 seconds.  This is quite
good compared to other hardware I've recently been looking at.

The ceramic resonator, on the other hand, is pretty awful.

Dennis Ferguson