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Old 16th Jan 2023, 8:11 pm   #1
Miguel Lopez
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Default And a high precision chrono too

I opened the other thread about digital voltmeters and I would like to share this one too. In this case I'm building a high precision digital chronometer for the same purpose of the voltmeters: to calibrate measuring instruments.

The chrono will be used to test and calibrate other chronos, timers, clocks but also optical tachometers and to a less extent frequency meters. It will use a Soviet hifg precision quartz crystal oscillator with an uncertainty of 10-4 seconds in 24 hours. The xtal is warmed by a control circuit to achieve such precision. Not a primary standard but definitively something useful to calibrate industrial instruments.

I intend that the chrono has two formats of counting:
1-) hours, minutes, seconds and hundredths
2-) Seconds and hundredths

I also intend that it can be operated directly from a button in the front panel as well as from another chrono via a control signal.
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Old 17th Jan 2023, 8:02 am   #2
Diabolical Artificer
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Default Re: And a high precision chrono too

Here's a pic of the funky Soviet xtal oven oscillator that Miguel sent me, are they 70's or 80's Miguel?

Andy.
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Old 17th Jan 2023, 2:18 pm   #3
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Default Re: And a high precision chrono too

Late 80s or early 90s. Not sure. It was the heart of a Soviet Ч6-31 frequency synthetizer like the one in the attached picture. The circuit oscillate at the fixed frequency of 1 MHz. The output is a sinewave so I need to "square" it and the divide it to get the 1 hundreth of a second signal that I need.
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Last edited by Miguel Lopez; 17th Jan 2023 at 2:42 pm.
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Old 17th Jan 2023, 8:27 pm   #4
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Default Re: And a high precision chrono too

This is the oscillogram of the output of the xtal oscillator.

1 MHz sinewave
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Old 24th Jan 2023, 3:34 pm   #5
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Default Re: And a high precision chrono too

These are the PCBs that I have etched to build the chrono. They are hand-painted and double-sided with a diferent circuit on each side
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Old 1st Feb 2023, 2:46 pm   #6
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Default Re: And a high precision chrono too

The 8-digit display is taking shape
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Old 3rd Feb 2023, 5:11 pm   #7
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Default Re: And a high precision chrono too

This is Side A (or B) of the PCB that contains the BCD-to-7seg decoders for the display. In this case they are chips from the former GDR, equivalents to SN7446 and SN7447, but this ones close the "6" and the "9". Resistors are Soviet MLT type.
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Old 6th Feb 2023, 6:00 pm   #8
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Default Re: And a high precision chrono too

The work from this weekend. The display block is already working and tested. It works as expected. Now I began to mount the frequency divider block to get the different frequencies that I need to test optical tachometers.

Chips are a mix of scavenged Philips CMOS and Tesla TTL.
Resistors are Soviet MLT
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Old 20th Feb 2023, 5:16 pm   #9
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Default Re: And a high precision chrono too

I did some advances this weekend. Here how the chrono is going...
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Old 6th Mar 2023, 5:21 pm   #10
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Default Re: And a high precision chrono too

Some more advances on the chrono.
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Old 13th Mar 2023, 8:51 pm   #11
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Default Re: And a high precision chrono too

I did some work on weekend. This is how the chrono is looking so far
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Old 20th Mar 2023, 7:04 pm   #12
Miguel Lopez
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Default Re: And a high precision chrono too

Finally I have the chron working, althought not at 100%. I found some design flaws while building it this weekend.

First, I have to add another CD4027 because I need to divide the 2,5Hz frequency cause I designed the frequency divider for a 12 steps selector and I finally got one with 14 steps. I added the 10 kHz output which was not originally intended and I want to add the 1,25 Hz too, to complete the 14 steps

Second, there is a detail that I did not have into account while designing it, that is it does not work on Hours:Minutes:Seconds (HMS) mode. It works only in "Seconds only" (SEG) mode. When in HMS the clock signal for the following counter must be taken from another line than when in SEG mode. Solution is "easy" but now I have to prepare a small PCB and add it to correct this problem. A couple of CD4011 will do the job so nothing to worry about,

So far it works nicely in the SEG mode and the outputs to test tachometers are OK, except for the output of 1,25Hz. Here some pictures:
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