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Are these capacitors suitable?
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Are these capacitors suitable?

by mrchuck on Sat Oct 03, 2009 10:55 am

Hello,

After a silly mistake when attaching the 20pF capacitors, I now need to buy two new ones :|

Could anyone tell me if these would be suitable? (they stock 18 or 22pF) - http://www.maplin.co.uk/Module.aspx?ModuleNo=304

I'd buy the ones listed on the parts list from Mouser or Digikey but the shipping will be very high (I'm in the UK). I do notice that the Adafruit partlist datasheet rates them as 18pF and not 20pF.

Daft questions, but I'm confused and hopefully someone can help.

Thanks
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Re: Are these capacitors suitable?

by adafruit on Sat Oct 03, 2009 11:22 am

yes, go with 18pf the clock may run a little fast by a few seconds a day (alternately, with 22pF it may run a little slow)

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Re: Are these capacitors suitable?

by mrchuck on Sat Oct 03, 2009 12:17 pm

That's great. Thanks for letting me know - I'll buy a couple of the 18pF and fit them properly this time.
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Re: Are these capacitors suitable?

by mctaylor on Fri Oct 23, 2009 4:48 pm

Beyond Maplin, you can also use suppliers listed in Amateur (ham) radio operator Ian White (GM3SEK)'s UK Component and Tool Suppliers list.

Farnell and Rapid Electronics as well as many other sources carry 20pF cermanic capacitors suitable for cheap.

20 pF ceramic capacitor, through-hole, radial leads, C0G / NP0 temperature coefficient, ~2.5mm lead spacing,

From UK Farnell: http://bit.ly/3tDgtA

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Re: Are these capacitors suitable?

by Autronius on Wed Jun 02, 2010 11:49 pm

I also suffered a tragic (and rather embarrassing) 20pf capacitor accident...

my local electronics part store carries 18pf and 22pf, but sadly no 20's.

I've read in a few different topics (from adafruit (ladyada?)...) with instructions to use either. I was sort of hoping for a one or the other, but it made me think.

What if I use 1 18pf and 1 22pf, would that balance out at a nice 20pf average? :D
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Re: Are these capacitors suitable?

by adafruit on Thu Jun 03, 2010 12:50 am

you should keep the two the same

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Re: Are these capacitors suitable?

by stinkbutt on Thu Jun 03, 2010 10:21 pm

Can anybody explain the maths behind why the capacitors need to be 20pF? I seem to remember something about the chip pin itself having a couple pF of capacitance and somehow that factors in as well, but I don't understand the WHY.
Red M&M, Blue M&M: They all wind up the same color

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Re: Are these capacitors suitable?

by adafruit on Thu Jun 03, 2010 11:29 pm


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Please be positive and constructive with your questions and comments.