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Creating a Vetinari Clock Using Antique Analog Meters

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GSKrasle
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Re: Vintage Time Delay Relay
GSKrasle   8/22/2014 1:45:59 PM
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And a Victorian-Size loop-filter!

antedeluvian
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Re: Sorry to have missed it
antedeluvian   8/22/2014 1:27:00 PM
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mhrackin

 Anywhere in the airport area works well; if you wait, you may have to stay in Cleveland!

OOO Cleveland! Rock 'n Roll Hall of Fame

Wnderer
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Re: Vintage Time Delay Relay
Wnderer   8/22/2014 12:47:09 PM
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@ GSKrasle Could you build a PLL with the relay cycling as input, and take a multiplied output frequency?


Imagine how many hours that would take to lock. You have a VCO generating about a 1sec output that gets knocked down to 1 minute pulses to be compared to the signal from the relay. The phase error is then used to adjust the VCO frequency until the error is really small. You'd need lots of 1 minute pulses for the loop to do it's thing and sync the VCO to the relay.

mhrackin
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Re: Sorry to have missed it
mhrackin   8/22/2014 12:30:13 PM
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Hamfest site is hamvention.org.  Dates for 2015 are May 15-17. We are at the Quality Inn Suites. On Maxton Rd,  is a solid mile of hotels and restaurants near the airport and convention center.  Currently reserved for Fri-Sun but could modify easily.  Joe and his wife (same schedule as us for now) likely not interested in the tour as they have been going since before they rename the Hamvention!

mhrackin
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Re: 32.768kHz crystals
mhrackin   8/22/2014 12:23:09 PM
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Another interesting property of the 32K tuning forks: their frequency vs. temperature curve is a parabols, with the peak right at 37C!  Your wrist is the oven..... also explains why a (properly trimmed) watch will lose time when off your wrist.

Clive
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Re: Sorry to have missed it
Clive "Max" Maxfield   8/22/2014 12:22:21 PM
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I think the IT guys have disabled links in comments due to spaming -- can you post the contact details for the hotel -- also what dates are the Hamfest? I was thinking that we could all drive up on Wed -- go on a museum tour (to be organized by Antedeluvian) on Thur -- and got to the Hamfest on Fri and Sat -- then drive back on Sun

mhrackin
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Re: Sorry to have missed it
mhrackin   8/22/2014 12:17:21 PM
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Talked to my friend Joe; he and his wife are going, and haven't missed ONE in at least 20 years!  They did warn that you need to make hotel reservations NOW as this is one of the major annual events at the convention center!  I made mine today, and there were few rooms left (at this hotel), and rates of course are high.  Anywhere in the airport area works well; if you wait, you may have to stay in Cleveland!

BTW, my wife is THRILLED at the idea!  Looking forward to the USAF museum etc.

GSKrasle
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Re: Vintage Time Delay Relay
GSKrasle   8/22/2014 11:40:57 AM
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Could you build a PLL with the relay cycling as input, and take a multiplied output frequency?

GSKrasle
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32.768kHz crystals
GSKrasle   8/22/2014 11:29:42 AM
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32768's are a peeve of mine, and their history is illuminating. The value was chosen (1970s?) for its obvious ease in converting to integral seconds, but it is difficult to get that value in the type of 'cut' that gets the best thermal stability ('A-T'), so a less-stable (and very small) one was used ('Tuning-Fork'). And hey! the thermal drift didn't even matter! if you have a reasonable-quality watch, look at the back. It's metal, isn't it? The front has an air-gap, and is therefore thermally-insulated. What is the temperature of the workings while the watch is securely strapped to your wrist? Pretty close to 37°, eh? Now take that tried-and-true ol' reliable crystal and put it in a desk clock, and thermal drift might surprize you.

Max The Magnificent
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Re: Analog meters
Max The Magnificent   8/22/2014 10:29:29 AM
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@bk11: Drive each meter lead with a seperate PWM.  The meter only cares about the differential.

Ooooh -- now that is a cunning thought....

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