Astronomical Clock

It looks like Tindie has linked me up with a maker who had the solution to a problem I’ve had for years.
I wanted to make an astronomical clock, like the Prague clock.
First you need an Astrolabe. As it turns out, I can make those.
Then you need to spin the part called the “rule” so it makes one revolution (360 degrees) in 24 hours. Easy, a cheap 24 hour clock mechanism can do that.

The step that stumped me for several years is the last bit. You have to spin the part called the “rete” so it makes one revolution (360 degrees) in one sidereal day.
I tried finding cheap sidereal clocks. I tried finding clock timer crystals cut to sidereal seconds. I tried figuring out how to use an Arduino driving servos. Nothing seemed to work.

Until I found Geppetto Electronics’ Tindie store and his Crazy Clock board. It had several options. I contacted him and asked if it could be modified to be a sidereal clock. He had it modified in about a day. He even suggested some 24 hour clock drives that were compatible.

I’ve got his board in the suggested drive right now ticking away on the wall as I type this. It seems to be the solution to my problem, at a very reasonable price.

Thanks Tindie!

@nyrath oh that is awesome! great story, thanks for sharing! and glad @nsayer could help!

Thank you so much for the kind words. I appreciate them more than I can say. I am so glad that my humble little creation was able to solve a problem for you and that it does so for years to come!

It turns out that between the Martian and Sidereal firmwares I was able to make a generic solution to make clocks that tick at virtually any constant speed (within the accuracy limits of the 20 ppm crystal and the mechanical tolerances), so if anyone else out there needs a clock at a different rate… it should be easy!

That will be super! I’m glad my request allowed you to generalize the solution.

Sometime in the future I will discuss with you making a Crazy Clock with a rate of one Tidal Lunar Day (24.8411 hours)

.8411 hours is 50 minutes, 27.6 seconds. Since the 20ppm tolerance is a second per day, it’s safe to round that up to 28 seconds. The clock is going to lose 3028 seconds every 86400. Dividing the former by the latter yields 28 + 1616/3028. You can’t reduce that fraction too much. Factoring the numerator and denominator shows that you can only pull 4 out of each. You’re left with 404/757. But that’s ok.

What you do is set up an outer “cycle” of 757 inner cycles. Each inner cycle is either 28 or 29 units (in the case of my board, each unit is 1/10 second). You do 404 cycles of 29 and (757-404) cycles of 28. At the end of each inner cycle (however long it is), you add an extra unit of delay.

So this is an instance of a “drift” clock, set to go slower, with a basic cycle length of 28, a cycle count of 757 and a long cycle count of 404.

EDIT: It’s in the store now.

Now That’s service! Thanks!