Pragotron Slave Clock

[renardiere7Participant @renardiere7]

I have a Pragotron Factory clock which my wife found as a pile of parts at a local Antiques Fair. I reglazed it, tidied things up and fitted it with as powerful a quartz clock motor as I could find. The hands are fairly heavy and after a few years this takes a toll on the motor which slowly fails. I have just ordered a new motor for the clock but I’ve started thinking again about the practicalities of fitting the original slave movement. From experimenting previously I’ve determined that it requires a 24v pulse every minute. This energised a pair of solenoids which “wound” a clockwork movement which ran for a minute. I don’t believe the pulse has to have polarity reversed as with the ? Lavet slave clocks just a belt of 24v of reasonable current every minute.

Given that my electrical knowledge is basic and electronics are a complete mystery my question is how easy would it be to contrive a device that kicks out a pulse of 24v on a precise minute interval?

Cheers!     Alan

[Michael GilliganParticipant @michaelgilligan61133]

Some background info.

https://pragotron.sk/?lang=en

MichaelG.

[Robert Atkinson 2Participant @robertatkinson2]

Very Easy.
First apparoach would be CMOS logic and a 32.768kHz crystal. First device is a HEF4060 a oscillator and 14 stage divider. The odd frequency provides a 1 second output with binary division. They are a standard part used in millions of clocks, watches and other devices. The 14 stages of the 4060 provide a 2^14 (16384) divison so a 2 Hz output. You then need a divide by 120 to get 1 per miniute.  This would take 3 or 4 16 pin chips.
Second option would be a PI microcontroller. Ideally this would run TVB’s PicDiv code http://www.leapsecond.com/pic/picdiv.htm
This code is specifically written in assembler for accurate division. Driven by any suitable oscillator.
You could also divide down the mains frequency. This has good averaged accuracy.
Drive to the coil would be a MOSFET transistor.

No doubt there will be suggestions to use a Arduino, RPi PICO or similar microcomputer. Persoally I find this overkill and unless care is taken accuracy can suffer (at least not meet my timenut leves) A lot of the low cost boards don’t even have crystal oscillators.

EDIT: Final Option: Use a geared syncronous mains motor (like those used in older anns clocks washing machine timers etc)  wit a cam wheel on the output operating a roller arm microswitch once a minute. E.g. a 1/2 RPM motor with two notches.

Robert.

[renardiere7Participant @renardiere7]

Thank’s both for very prompt replies.

Michael, that website looks very useful and possibly new since I last researched this (5yrs ago?) Thanks.

Robert, thanks but most of that is so far above my head it’s leaving con-trails. However I can handle the washing machine timer with cam and microswitch that is right up my street. Regarding a 24v DC supply I vaguely remember trying an old laptop or similar charger that was 24v DC out but it didn’t have sufficient oomph to drive the solenoids. Short of a couple of old car batteries in series (which did work) any recommendations as to a power supply?

Thanks very much

Alan

[Robert Atkinson 2]

On Robert Atkinson 2 Said:

Very Easy…

No doubt there will be suggestions to use a Arduino, RPi PICO or similar microcomputer. Persoally I find this overkill and unless care is taken accuracy can suffer (at least not meet my timenut leves) A lot of the low cost boards don’t even have crystal oscillators.

…

Robert.

Well, here’s an Arduino solution, more or less complete, that can be built at home.   It’s not a list of suggestions requiring electronic skills.

The circuit:

Arduino Leonardo recommended because it has a crystal oscillator.  About 100ppm, similar to a good mechanical watch.  Easiest way to power it is with a 5V USB wall-wart plug.

I’ve used a relay module, described here, because it handles the volts, and isolates the Arduino from any spikes caused by the Pragotron’s solenoid.   Very simple.

The program is also simple.  Given the required frequency in hertz, this online calculator outputs a complete ‘blink’ program.  It flashes the onboard LED and pin 13.   The hardware timer in a Leonardo goes down to about 4 seconds, so I asked for one, and will show how to make the required 60s from that.  This is the 1 second program:

To get 60 second pulses, modify the ISR code at the end to this:

No need to install the Arduino IDE or to learn C, or write a program..  The code can be compiled online and blown onto the Leonardo from here.  A free account is needed.

There are some gotchas:

• where the 24V comes from (Maybe a battery – depends on how much current the solenoid draws and for how long.)
• Alan doesn’t specify what he means by ‘precise’.  If better than 100ppm is needed, I’d add a RTC module (about 20ppm) , and use it’s seconds pulses.  The program is different – let me know if needed.
• I’ve assumed the 60 second pulses can be a square wave, with 50% duty cycle.  That’s heavy handed, and maybe something like ON for 0.1S, and OFF for 59.9S is wanted – it depends on how the solenoid ticks the Pragotron.   If the duty cycle needs to be changed, it’s done by tweaking the program, no hardware change required.

Taken me much longer to document than to do!

Dave

 

[Peter Cook 6Participant @petercook6]

You could of course always buy the necessary driver. One like this one

[Robert Atkinson 2Participant @robertatkinson2]

A 50% duty cycle will probably burn out the coil in the clock.
The question was how easy would it be. That of course depends on your skill set. Which is harder, wiring up some IC’s or setting up to progam an Arduino? Its apples and oranges. If the OP is mostly a mechanical / clock making then my final suggestion of a motor and switch may be best fir them.
Since posting I looked at the link posted by Micheal G and it looks like Pragotron used contact discs to generate pulses.
Such an arrangement could be made as an attractive item in it’s own right.

Robert.

[renardiere7Participant @renardiere7]

Wow!  Thanks, more suggestions. Arduino’s like electronic components are not only out of my skill set range but I lack the tool kit to deal with this sort of thing. I wouldn’t say I’m computer illiterate but have never done any programming other than tinkering with Basic back in the Eighties.

Peter, looks like you found the ideal solution, looks pricey but still manages to avoid the need to run cables to the clock which is a bonus. Again I remember searching for information on Master clocks in the past but it was all historical documents, certainly nothing like that seemed to exist then.

Thanks all.

 

Alan

[duncan webster 1Participant @duncanwebster1]

Or one of these, similar price

https://www.electric-clocks.co.uk/ImpulseDrivers/slaveclockdrivea.html

[renardiere7Participant @renardiere7]

Thanks Duncan, even more options.

 

Alan

[Robert Atkinson 2Participant @robertatkinson2]

I had a look at my easily accessible stock of synchronous motors with gearboxes and the slowest is 15 RPM. That would require a couple more gears to get to 1 pulse per minute from a switch.
Another option would be to use a quartz clock module with a opaque disk on the seconds staff. This then has a notch on the outer edge that is sensed by a slotted opto. This switches a MOSFET transistor. You can get modules for the sensor and MOSFET Some fairly random examples from ebay:

https://www.ebay.co.uk/itm/232516162353 and http://www.ebay.co.uk/itm/232518999508

or

http://www.ebay.co.uk/itm/295165117526 and https://www.ebay.co.uk/itm/296813925518
You also need a 5 V regulator like this https://www.ebay.co.uk/itm/295640412774

These are easy to wire up.

Or I could knock something up for you…

Robert.

[renardiere7Participant @renardiere7]

Robert, that’s a very generous offer. Thank you. I think what I’m going to do is study the many options suggested above and pick one. Although I’m inclined towards an off the shelf solution I’m not ruling out going down the diy route, after all every day should be a learning day.

Thanks all for your inputs, I’m so glad I joined this group.

 

Alan

[John HaineParticipant @johnhaine32865]

One thing to bear in mind is that these clocks are normally impulsed only one way, and twice a year they have to be shifted 1 hour forward or back. This can prove tedious especially if you miscount. Ideally the pulser would give you an automatic option for both by one means or another. I don’t know if the commercial devices do this. It would be even better if it was automatic on the appropriate dates.

[John HaineParticipant @johnhaine32865]

<p style=”text-align: left;”>A small caveat about the first of the opto switches that Robert linked to. They have an lm393 wired as a comparator with no hysteresis and oscillate as they switch. Might not be a problem but made them useless for pendulum sensing.</p>

[renardiere7]

On renardiere7 Said:

… Although I’m inclined towards an off the shelf solution I’m not ruling out going down the diy route, after all every day should be a learning day.

…

 

Alan

Next step is to find the solution that fits the situation best, which depends what you know (or have time to learn), and the tools you have (or are prepared to buy).   And, as always, how much time and money is available.

Some thoughts:

• The off the shelf units identified by Pete and Duncan are the easiest and quickest solution.  Unfortunately, they are also the most expensive, especially because power supplies are needed too.   Batteries are an easy answer, but cost more in the long run.
• Robert and I both know enough electronics to make designing and building one of these a doddle, and we have soldering irons, test equipment and stock components.  It’s almost trivial.   Not so easy for a beginner starting from scratch, who has to buy a set of tools he might only use once, and get his head round basic electronics.
• We, and others, know enough about microcontrollers to make that route a doddle too.  Robert said a microcontroller was overkill, but I’d rather slaughter cattle with a humane destroyer rather than a DIY spear.  And, because the modules are mass-produced, the Arduino solution is cheap.   In this case, no need for special equipment or programming.  But again, not easy for a beginner who only wants a quick one-off.
• Those happy with mechanical solutions might well prefer an arrangement whereby a synchronous electric motor drives a gear-box, which turns a cam once per minute and operates a home-made leaf spring switch.  Obvious how it works, but  gears have to be sourced and mounted, and the cam needs thought.   Motor likely to be noisy too, and inefficient.  Also possible to modify an existing clock, how easy depends on the clock!

 

The decision might come down to how much Alan fancies a learning experience.   If Alan not interested and on a limited budget,  then Robert’s offer is a good one!  The Arduino solution is cheap too, and not as scary difficult as Alan imagines: Leonardo £13.60 from RS Components, relay between 32p (from China) and £5 from a UK retailer, USB Wall-wart £7.    But I’m assuming Alan owns a soldering iron and a PC…

Dave

 

[duncan webster 1Participant @duncanwebster1]

2 other things to consider

You can strip the timer circuit out of a quartz clock to give you a pulse once every 1 or 2 seconds depending on how you wire if up

Ive made a clock which divides the mains by 50 to get a one second pulse. You could add a further divide by 60 to get one minute. Just uses cascaded counters

[Robert Atkinson 2Participant @robertatkinson2]

Dave, Couple of minor points (yes I’m a pedant) I actually said a microcomputer was overkill. As discussed in another thread I put the Raspberry Pi products and higher end Arduino’s in this class rather than microcontrollers.
The project needs a 24V supply as well as 5V wall wart. That said I’d consider a low power step-up coverter (1W 5V to +- 12V e.g Murata NKE0512) charging a 10,000uF capacitor via a 680 Ohm resistor during the off period to provide a good high current pulse. Might even go to 30V (+-15V) to give a bigger kick to the coil.

Robert.

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