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GSKrasle
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Freelancer
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
User Rank
Freelancer
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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Blogger
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....

bk11
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Manager
Re: Analog meters
bk11   8/22/2014 10:11:22 AM
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#3 Drive each meter lead with a seperate PWM.  The meter only cares about the differential.

Crusty1
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CEO
Re: What no Sun Dial
Crusty1   8/22/2014 7:49:47 AM
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Hi David, i like the way you are thinking, would this make a Kickstarter project?

I suspect I am the only idiot that would think of this as a saleable product, but you do see so much similar tat in these home buying magazines.

I suppose I should try and make it as green as possible and get it sun powered? or wind or water?

Lots to think about on this one.

DrFPGA
User Rank
Blogger
Re: Vintage Time Delay Relay
DrFPGA   8/21/2014 9:20:32 PM
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Another solution, mechanical this time- built for longevity...

http://longnow.org/clock/ 

Wnderer
User Rank
CEO
Re: Vintage Time Delay Relay
Wnderer   8/21/2014 7:34:23 PM
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@DrFPGA If you pre-heated it to the right temp could you get it to switch every second?


Probably not. We're talking about something thermal that probably needs a large piece of hysteresis between the heating turn on and cooling to turn off. If you kept it heated up it would never turn off. You would need to use a higher voltage which might damage the tube or you could control an external heater to increase the rate of heating that shuts off when the relay goes on.

Reading Max's article again, it probably doesn't fit into his Vetinari Clock concept. It just the way my brain segways. I would use the relay to trigger the up/down counter on a 64 tap digital pot like the AD5113 and use a comparator to reset the pot when it hits 60. The comparator would trigger another digital pot that resets at 24 or 12.  An all analog solution with no programming.

DrFPGA
User Rank
Blogger
Re: Vintage Time Delay Relay
DrFPGA   8/21/2014 6:37:29 PM
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If you pre-heated it to the right temp could you get it to switch every second?

DrFPGA
User Rank
Blogger
Re: What no Sun Dial
DrFPGA   8/21/2014 6:35:20 PM
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and it works in the dark too!

David Ashton
User Rank
Blogger
Re: What no Sun Dial
David Ashton   8/21/2014 4:56:46 PM
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@Crusty...GREAT idea.  You could have a curved line of RGB LEDs some distance above the sundial to simulate the sun, clear ones that have a narrow beam. and illuminate them one at a time, changing every 10 minutes or so (this implies 72 LEDs for 12 hours) and use one colour for day and another for night.  Wouldn't need any motors, just some electronics to drive the LEDS.  Since your LEDs would be fixed you wouldn't need to compensate for the seasons either...

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