Elektronika 7-06 clock replica

A very-modern take on the popular late-80s soviet clock.

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So my neighbour drove to visit his parents on the weekend and brought back this janky old clock. It was the smaller soviet-era clock with seven segment display but i realized that only after tearing that thing down since it didn't work at all!

And while I was troubleshooting it my neighbour was telling me how these kinds of clocks are sought after like crazy and then he said he's got the big one - the Elektronika 7 at his parents house and I recalled instantly seeing one in various locations here in Lithuania. I even remember seeing one in Chernobyl TV series!

So after arguing needlessly hours on end about the way the replica was supposed to be built we came to the conclusion that I should make the LED version of this (the original had VFD tubes) and that he won't be participating in this project:D

Okay here's the specs:

  • Dimensions: same as the original, measured from photos.
  • Display: LEDs for every dot (found one one that light up in the exact same color as the phosphors in the original VFDs). That's 266 LEDs. LEDs shall be housed in a plastic matrix frame with holes filled with frosted semi-transparent resin (just like how seven segment LED displays are constructed).
  • Power required: 

     One LED draws  2.9V*0.01A=0.029W

     All LEDs shall therefore draw 0.029W*266=15.25W

  • Power supply: 9V/12V adapter (because I have plenty of those from previous projects).
  • Interface: IR remote control (because the clock will be hanging on the wall somewhere beyond physical reach)
  • Construction: Front panel - dark green transparent plexiglass 660mm x 210mm x 3mm. Main frame holding the PCBs - matte black plexiglass 660mm x 210mm x 3mm. The rest is 16mm thick wooden frame around the plexiglass. Holding everything will be a combination of 3D printed spacers and screws. No buttons (unlike the original, very modern though).
  • IR Remote: The remote shall have 5 buttons: timer, plus, minus, set, date/time.
  • Timekeeping: Real Time Clock chip with crystal source and a backup super-capacitor.
  • LED driver: no driver, just MOSFETs and an adjustible voltage Buck regulator (for dimming).
  • Brains of the device: STM32L0 series MCU and a bunch of GPIO expanders to control a bunch of LEDs. Maybe a seprate MCU to decode IR signal from the remote. Might be cheaper that using larger STM32 MCU with lots of timers. (I use like 2 timers for decoding IR). 


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  • Final assembly & calibration

    makufelis-xyz08/22/2020 at 11:13 0 comments

    With not much left to do here I assembled the final LED boards. After hooking them up I noticed that some of the LEDs had a slight tint towards blue which I'm pretty sure is a consequence of overheating while soldering so definitely something to take into consideration for later assemblies.

    Another thing I did was to calibrate the RTC clock so it runs in tune with the atomic clock. Since this clock doesn't have WiFi or GPS syncing ability the calibration is a must IMO.

    So to calibrate the RTC i connected a frequency counter to SEC_INT/CALIB_OUT and held TEST1 low. That way the clock entered calibration mode where the RTC chip outputs its current running clock of 4096Hz at SEC_INT/CALIB_OUT and I could compare it to reference clock of 4096Hz and then calculate the deviation in ppm.

    So the clock was speeding at +55.8ppm which might in part be a result of me not putting any crystal capacitors which makes the crystal frequency go up but it's fine. 

    Oh, and I made the typical rookie mistake of not putting in I2C pull-up resistors in the schematic so I had to fix that.

  • Enclosure bussiness

    makufelis-xyz07/20/2020 at 19:24 0 comments

    Hello again!

    The LED assembly that I made looked too bright so I've been trying to find ways of diffusing the individual pixel LED and came up with a cheap and repeatable way of doing it which is filling the pixels with translucent hot glue and it worked wonders!

    Currently I only have one and a half LED assemblies made - looking forward to receiving the rest 130 LEDs to complete the clock.

    Meanwhile my neighbour cut out the wooden panels for the enclosure and they look amazing. My neighbour put an extra step and painted them with this very nice varnish, makes em look more authentic.

  • Success with PCBs

    makufelis-xyz05/29/2020 at 13:45 0 comments

    Got my PCBs from china, assembled them and got it working the first time wich is kinda suspect but I'll take it! 

    Started with testing the digit boards, the variable power supply then the ambient light sensors, oh and the infrared receiver..

    Next step is to test the RTC clock and backup supercap circuit to see if it will last atleast a day on backup power..

  • Schematics..

    makufelis-xyz04/06/2020 at 18:03 0 comments

    Alright, the schematics and PCB are done and I drew in parts that I already have hoarded over the years so there's gonna be a mix of parts with packages ranging from SOT-23 all the way to BGA which I'll be assembling by hand so we'll how this will pan out. 

    The buck regulator for LEDs will be a particularly tricky one both in terms of assembly and making it work since its this wacky dual phase topology which is new for me so looking forward to exploring new avenues of power design..

    Oh and controlling the voltage of the regulator using a digi-pot also is an intriguing topic in itself..

    So yes, the LEDs will basically be connected in parallel from the high-current 2.5V-3V adjustible voltage bus. That should make the LED segment driving way easier.. or..will bring some issues with unintentional LED dimming during heavy current load..

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