[time-nuts] Mechanical clock sound pickup circuit

Alexander Pummer alexpcs at ieee.org
Sat Dec 12 16:28:15 EST 2015


Once upon the time there was a "Vibrograph", see nice pictures here: 
https://www.google.com/search?q=vibrograph&tbm=isch&tbo=u&source=univ&sa=X&ved=0ahUKEwigtcmSn9fJAhUW8GMKHVNyAMcQsAQIHA&biw=1760&bih=888 
,which picked up the sound of watches, clocks, and the watch maker was 
able to set the watch very accurately, these machines did not used any 
fancy DSP despite that they worked very well, I myself used one some 55 
years ego in Switzerland,.
to get a reliable digital signal from a noisy analog signal is the most 
reliable way to use an analog PLL with a linear multiplier type phase 
detector  [ at least one input of the phase detector must be linear e.g. 
a transitional gate [cd4016 and it's derivatives ], the noise could be 
filtered out with a low pass filter or integrator, the price of the 
method is that it also eliminates the phase-noise of the the input signal, .
That was the method which was used by the Vibrograph.
73
LJ6UHN
Alex

On 12/12/2015 7:15 AM, Dave Martindale wrote:
> Someone is in the process of writing open-source watch timing software.
> You may want to look into it.
>
> It was announced here:
> http://forums.watchuseek.com/f6/open-source-timing-software-2542874-post21977314.html#poststop
>
> It contains these links:
> First the goodies. Here are Windows binaries
> http://ciovil.li/tg.zip
> and here is the full source code
> https://github.com/vacaboja/tg
>
> Apparently this software is better at dealing with noisy signals from
> microphones than Biburo.  Since it's open source, you can see what it's
> doing internally.  It expects an analog input, and does its own filtering
> to find the interesting edges within the sound of each tick.
>
> The precision with which you can time events is likely to be limited by the
> frequency response of your sensor and the amplifier.  If that's limited to
> 20 kHz, a standard PC sound card is adequate.  For up to 80 kHz or so, you
> can buy a relatively inexpensive USB "audio interface" that digitizes at
> 192 kHz (typically 24 bit resolution).  At somewhat higher cost, you can
> get professional audio interfaces that accept an external clock source.
>
> - Dave
>
>
> On Fri, Dec 11, 2015 at 1:44 PM, Andrea Baldoni <erm1eaae7 at ermione.com>
> wrote:
>
>> Hello!
>>
>> I decided to do some experiments with mechanical clocks, so I worked a
>> little
>> on picking up escapement ticking sound, with the idea of processing it and
>> obtaining a "clean" digital pulse to feed a counter.
>>
>> So far, I have not yet been able to find the best way to obtain a digital
>> pulse,
>> but I have already built the preamp for the piezoelectrick pickup, that
>> I used to feed the mic input of a PC sound card for spectrum analysis.
>>
>> The timing could eventually be done in software because the whole idea of
>> measuring watches by picking up their noise almost surely doesn't allow
>> high
>> resolution anyway, but I will plan to try hardware solutions as well in the
>> future. I hope to be able to measure the jitter of the clock, but it will
>> be
>> very hard.
>>
>> In the meantime, with the free software Biburo you can download here
>>
>> http://tokeiyade.michikusa.jp
>>
>> you can regulate your wrist watch.
>>
>> Best regards,
>> Andrea Baldoni
>>
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