Pragotron Slave Clock – Part 4 – Odd’s and Ends

Given that my clock driver is complete and seems to work quite nicely I think I will move on to other projects however if anyone else is considering building their own variant to drive a vintage clock then I’ll leave just a couple of extra notes:

The connections I used were as follows:

LCD Driver : RS Pin 9, Enable Pin 8, 4 bit Data on Pins 7,6,5&4.
Clock Module: Data in on Pin 2, Power control on Pin 3.
H-Bridge Control: Enable A5, Direction1 Pin 12 and Direction2 Pin 11
Buttons on pins A3, A2 and A1.

All these can be changed in software if required.

If your clock does not require alternate pulses to change polarity then you don’t need an H-Bridge, just drive the voltage you need using a single FET.  Beware however that the coil in the clock is inductive so a scrubber diode might be advisable.

My menu system is very simple: RUN, SET, TZDIF, MANUAL and VERSION.  The first button changes mode with a long press, the other two buttons are up and down.

The controller needs to be told the current state of the hands when first powered using the MANUAL setting and thereafter it remembers the hand position even during power failure by recording the current state in EEPROM.  I use a levelling technique to reduce wear on any one EEPROM location, simple and should last the lifetime of the device.

Finally, be aware that the polarity of the clock does matter!  A pulse of the positive polarity will have no effect if applied when a negative pulse is required and vice versa.  Easily sorted out by swapping if you find yourself appearing to be one minute out and unable to advance.

Have fun and keep those vintage clocks in their original form!

And a nice video of the smaller version of my clock being made…


About nivagswerdna

Professional Geek
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5 Responses to Pragotron Slave Clock – Part 4 – Odd’s and Ends

  1. oliverb123 says:

    Hi I am working on a driver for a 44cm square Pragotron clock that had been converted to quartz at the shop. I have a PS100 movement sourced from Eastern Europe but could you let me know the model of the movement fitted in your clock? I think there are many types of movements and my PS100 may be too small for this size of clock.

  2. Mark says:

    Try one of the V.KEL SIRF-3 (aka VK16E) GPS modules from Ebay (around $7 each). Mine can track satellites sitting on the bottom floor of a 2 story stucco over wire mesh house, away from windows, with the patch antenna upside down and facing the earth… not bad for a $7 GPS module (when I bought mine they were 3 for $15 shipped. I figured that they would be crap, but they are definitely not)

    • nivagswerdna says:

      Being 1575.42 MHz the GPS L1 signal really shouldn’t work indoors so I have disregarded using a GPS receiver up to now but I’ll try out your suggestion. The reason I have been using MSF60 and DFC77 radio is that I wanted something that would work in a number of environments especially for another project which is a desk clock for work (where I am in a modern steel frame building and away from windows… I will get a VK16E and report back. Thanks for the comment.

      • Mark says:

        The GPS signal strength is below the noise floor when it gets to earth. De-spreading the 1 MHz signal into a 50 bits/second one is where the GPS sensitivity magic occurs and boosts the effective signal strength to a usable level. It does take longer than normal to get the initial lock on the GPS signals indoors. Once that is achieved it can maintain the lock quite well. I did a one week log and it did not have a single missing time stamp.

        I have tried LOTS of different GPS receivers and the Sirf-3 seems to work the best in poor signal situations. I suspect that if you replaced the small patch antenna with something better it would work even better. V.KEL has a Ublox version of the module but it does not work nearly as well indoors.

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