A Sidereal Clock: Teardown, Analysis, Adjustment

[@kilosierraalpha]

Hi, thanks for the video and hope you're still well. Miss the videos!

[@KeritechElectronics]

As always, cool stuff :)

[@das250250]

Where did you get to Roger

[@KainkaLabs]

New videos come out in a few weeks. I was extremely busy in the last 3 years.

[@isidoromaich7226]

@@KainkaLabs in this channel?

[@el_sturlo]

Very interesting, thank you

[@soldiersvejk2053]

hope you are doing well！

[@DirkJMartens]

Hi ... nice project and video ... learnt something about astronomy as well ... Could you share more details on that frequency meter? ... I think you mention Electron or Elector magazine? ... any schematics? ... was it a kit?

[@KainkaLabs]

It was published by Elektor magazine in 1985. You can download the article series as registered elektor-member (or buy it as a non-member?) from here: www.elektormagazine.com/magazine/elektor-198501/45402 It was at that time top-notch because it was the first "amateur" universal-counter that kept the full (selectable) 6- oder 7-digit accuracy over the whole frequency range by applying the principle of a "reciprocal counter" which is only feasible by using a microprocessor to do the math (here a 6502). It uses a beautiful alphanumeric vacuum fluorescent display and a membrane keypad and dozens of logic-ICs, some of them very special ones. At that time you could buy a full kit or only the hard-to-get parts (PCBs, VFD display, keypad). I choose the latter option, bought all the ICs and other parts separately and typed in and then programmed the EPROM content with the firmware by hand. The case is full of PCBs, some of them attached as vertical daughter boards to the main PCBs. Later I added a home-build OCXO which you can see attached on the left side of the case. It is one of my favourite instruments partly because of the beautiful display and the well thought out concept of the counter.

[@DirkJMartens]

@@KainkaLabs Thank you ... will definitely have a look at this ... from the outside it indeed looks beautiful... and from your description even nicer on the inside

[@SeanBZA]

Easy enough to ovenise that crystal though, especially if it is mains powered all the time, you make a small insulated cover that attaches to the crystal, and inside the cover you put a PNP power transistor and a NTC thermistor to control base current, so that the transistor runs as a linear resistor and heats up, with the NTC robbing base current from it, so that you can set the temperature to a temperature a bit above expected ambient. Temperature just depends on having a well regulated supply to the heater, so another 5V-10V regulator to feed it, and it will keep the crystal at a constant higher temperature. PNP do the collector is grounded, and thus can contact the crystal case and not introduce noise, though it is electrically isolated from it. At least an order of magnitude better in stability, though it does drift on power up a lot, after which is stabler than bare crystal. Best to also insulate the oscillator IC, and a metal tab to keep it at crystal temperature, and insulation under the area of board. Even better as well power oscillator from it's own power supply.

[@KainkaLabs]

I even thought about that. You can see on the left side of the frequency counter a home-build OCXO attached to the case, where I copied a circuit from the German ELV electronics-magazine. I could use the same circuit for ovenizing the crystal in the clock. But there are 2 problems: The transformer doesn´t have enough power to supply both the OCXO in the heating phase and the 7-segment display with full brightness. And even if I added a secondary PSU for the OCXO, you can´t guarantee that the mains-current is always 24/7 on. Someone could accidentally unplug the clock or there could be a power-blackout. It´s easier to check the clock with a smartphone app for sidereal time at the beginning of an observing session :-)

[@DAVIDGREGORYKERR]

A phase lock look that locks to the GPS satellites might make the sidereal clock more accurate.

[@KainkaLabs]

You still have the problem of power failure and need a UPS. A modern version would get time, date and longitude from a GPS receiver and calculate the local sidereal time from that data every second. That way you don´t need a UPS in case of power failure.

[@johncoops6897]

Just imagine the _Flat Earthers_ trying to explain this concept!

[@ghamor7590]

Looooooool