Yeah... I guess using a variable cap for one of them is a good idea?
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Yeah... I guess using a variable cap for one of them is a good idea?
"I think fish is nice, but then I think that rain is wet, so who am I to judge?" - Douglas Adams
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I don't think so, but that's just me.Originally Posted by Kamikaze47
I would think a variable cap would have more +/- over a temperature/voltage/sun angle range () range than a standard cap.
And don't forget...when you're trying out those 'standard caps' and you're looking for accuracy, a lot of caps have tolerances as wide as something like +80%/-20%. You can get ones that are tight, but they'll cost you.
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The problem is, if its going to be trial-and-error to work out the right value, i'm going to need a lot of caps.
"I think fish is nice, but then I think that rain is wet, so who am I to judge?" - Douglas Adams
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That's a fact.
But you've also got a completely configurable PIC that you can program in a bunch of correction values into.
(i.e. crystal is off 1%, program in 1% compensation).
So, as I see it, you only need 2 capacitors and a bit of math.
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Microchip also has a couple of app notes on the osc circuitry that you might want to check out
Tim Barr
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I don't think the Value matters as much as the 2 capacitors being the same.
Another quote from the datasheet...
Higher capacitance increases the stability
of the oscillator, but also increases the
start-up time.
If you have different value caps then it will change the frequency.
I've been using some 12pf caps that came with the 32768 crystals I bought. And it keeps real good time.
DT
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