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Author Topic: Crystal Driver Circuits  (Read 783 times)
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I have another question in my pursuit of happiness creating a 74 logic series clock.
anyway, I am using a 1Hz clock to drive the clock... but obviously 1Hz crystals are not sold. So I am using a 65.536kHz crystal and dividing it down, but can someone help me with driving the crystal? I can't find any solid explanations and/or circuits. btw I am not using a micro... just passives and 74 series ICs. I don't need EXTREME accuracy, preferably a simple and easy to build driver circuit.

Thanks a bunch!
baum
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You can use a standard Arduino UNO and load the basic beginner scetch called "Blink". Then you can correct the ON-time to 500ms and the OFF-time to 500ms. The whole cyclus will be 1sec. This is 1Hz.
Cost you about USD20. You will need a 5-12VDC (0.2A) powersupply also. (And purhaps a 817C optocoupler. And maby a BC-337 transistor + 22Ohm resistor).
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What is wrong with this one, google second hit:-
http://www.electronicecircuits.com/electronic-circuits/ttl-crystal-oscillator-schematic

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So I am using a 65.536kHz
Why so very high? There is no need.
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You can also use the old 555 to get 1Hz I belive
See this schematic http://electroschematics.com/4843/1-hz-pulse-generator/
« Last Edit: June 14, 2012, 11:50:24 am by HugoPT » Logged

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555 would probably be easiest, and easiest to adjust
Otherwise with a crystal that would be alot more hardware, and u need an oscillator for the crystal, so isn't effectively any better
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yeah, I used the old faithful 555 timer to replace a burnt out bi-metal timer on my kiln. With a big enough cap and a potentiometer, I was able to get a duty cycle of over a minute. It cost me $.60 to build.
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So you think that a 555 free running oscillator is going to be good enought to keep time in a clock.
You need a crystal to keep reasonable time.
But you don't needit that high. You need to learn how to make a divider that is not a power of two. This is very easy and means you can use a wide varity of crystals.
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Most people who use a crystal for clock work use a 32.768KHz one - they are ten-a-penny, and just as easy (easier - one less step) to divide down to 1Hz.

The thing with a crystal is it doesn't readily oscillate by itself.  You use it with an oscillator to regulate and control the frequency.  The crystal resonates at the specified frequency, and drags the oscillations of the existing oscillator in to line with it.

You have to have an existing oscillator that is working at roughly the right frequency already.

The simplest oscillators are made from one or more simple logic gates (NOT, or NAND), some resistors, and a capacitor or two.

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If crystal control is not an absolute requirement, and you have access to the secondary of a transformer, I have a mains-powered 74xx clock that uses the frequency reference below. Very good long-term accuracy. Size the voltage divider resistors as needed depending on the transformer. 7413s may be scarce; I believe 7414s are available though and should work just as well.


* schematic.png (2.71 KB, 844x238 - viewed 11 times.)
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