1pps signal for old Nixie Clocks?

[Dekatron42]

Hi,

I just bought an old Nixie clock design by "Karlsson" that uses a 1pps signal generator from what looks like a standard electronic clock with hands, I also found this "inner look" at another Karlsson clock that confirms what my clock contains more or less : http://www.nixie.dk/~jthomas/autopsy.html

What I wonder now is if anybody has hooked up a DS3231 with a small microprocessor to set it to output a 1pps signal on its output?

The current 1pps generator has a big spread in time so it is sometimes one minute ahead and sometimes a minute behind but it also drags behind every day and I'd like to do the simplest update to the circuit and I couldn't find anything simpler with better precision than the DS3231 and then program it to output 1pps - if you have another idea on how to do this I'm all ears!

Using a frequency divider on the 32KHz output would also be possible but I couldn't find any small chip that divided that right away.

I don't have good GPS reception in my apartment, otherwise I would have used a small GPS-unit.

/Martin

[gregebert]

You can program the DS323x to generate a periodic interrupt, which includes 1Hz. I've never actually used this feature, but I know that the DS3232 is very accurate. I'm seeing about 1 second/per month of drift.

[Paolo Cravero]

Hi.

I use the SQW output of Maxim RTC ICs (or clones...) in my clocks. It is 1 Hz/pps but I never measured its jitter: I read the time over the I2C bus periodically. I believe they are related so on the long run you get the same accuracy. And my cheap ds3231 modules are right on spot! 

My Arduino code in on github. Code snippet to activate the one pps:

    Wire.beginTransmission(0x68);

    Wire.write((byte)0x0E);

    Wire.write((byte)0x00); // control byte to set and enable 1 Hz SQW output &B0000_0000

    Wire.endTransmission(); /

Paolo

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[Dekatron42]

Paolo, that is exactly what I was thinking of! Now I have to get a programmer and a small PIC or something similar and experiment with it!

/Martin

On Sunday, 29 January 2017 21:38:11 UTC+1, Paolo Cravero wrote:

Hi.

I use the SQW output of Maxim RTC ICs (or clones...) in my clocks. It is 1 Hz/pps but I never measured its jitter: I read the time over the I2C bus periodically. I believe they are related so on the long run you get the same accuracy. And my cheap ds3231 modules are right on spot! 

My Arduino code in on github. Code snippet to activate the one pps:

    Wire.beginTransmission(0x68);

    Wire.write((byte)0x0E);

    Wire.write((byte)0x00); // control byte to set and enable 1 Hz SQW output &B0000_0000

    Wire.endTransmission(); /

Paolo

Il 29/Gen/2017 20:36, "Dekatron42" <martin....@gmail.com> ha scritto:

Hi,

I just bought an old Nixie clock design by "Karlsson" that uses a 1pps signal generator from what looks like a standard electronic clock with hands, I also found this "inner look" at another Karlsson clock that confirms what my clock contains more or less : http://www.nixie.dk/~jthomas/autopsy.html

What I wonder now is if anybody has hooked up a DS3231 with a small microprocessor to set it to output a 1pps signal on its output?

The current 1pps generator has a big spread in time so it is sometimes one minute ahead and sometimes a minute behind but it also drags behind every day and I'd like to do the simplest update to the circuit and I couldn't find anything simpler with better precision than the DS3231 and then program it to output 1pps - if you have another idea on how to do this I'm all ears!

Using a frequency divider on the 32KHz output would also be possible but I couldn't find any small chip that divided that right away.

I don't have good GPS reception in my apartment, otherwise I would have used a small GPS-unit.

/Martin

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[Paolo Cravero]

On Mon, Jan 30, 2017 at 11:23 AM, Dekatron42 wrote:

Paolo, that is exactly what I was thinking of! Now I have to get a programmer and a small PIC or something similar and experiment with it!

Choosing a microcontroller will be harder than everything else: too many options!

Unfortunately DS3231 does not permanently store information on the 1 pps output, which is disabled by default (like applying power or replacing the backup battery). I have not tested if the SQW output runs even if the RTC chip is in the uninitialized state, i.e. when power is first applied without the backup battery. So you may consider sending both a fictional but valid date/time and enabling the 1pps output every time power is applied.

If I had to do it I would probably use an ATtinyXYZ running on the internal RC oscillator and an Arduino bootloader for ease of programming (I have some Attiny85 DigiSpark boards that would do that).

Paolo

[Dekatron42]

A small update. I used a DS3231 and hooked the 32KHz output to a 74HCT4060 and after that a 74HCT74 to produce a 1Hz signal and that worked very well. I'm now trying to set up a programming environment so that I can try a PIC processor too.

I found out that the small module in the "Karlsson" clock was supposed to drive a stepper small motor as it had two outputs, 1/2Hz each, which had to be combined in the nixie clock to produce the necessary 1Hz pulse.

/Martin