Beginner Cap Value Difficulties

J

jack0987

Member

• Apr 23, 2010

• #1

It's hard when you are a beginner.

I have a circuit diagram using a crystal with two caps of value 20pf.

I went looking in my parts box and found two disk caps marked .0022 and a couple marked 22k.

Will these do?

I knew once how to figure these out, but it has been a long time and I do not remember.

 

bychon

New Member

• Apr 23, 2010

• #2

The .0022 is 2200pf. I'm not sure about the 22k. Somebody else will answer in a few minutes.

 

J

jack0987

Member

• Apr 23, 2010

• #3

Thankyou bychon.
I found a packet of disk caps with a label that says 15pf and the caps are marked 15k.
Following that, the 22k may mean 22pf.
Assuming they are in fact 22pf, could I use them or should I get the 20pf the circuit diagram calls for?
Will the slightly higher value of 22pf throw the timing off?

 

Mikebits

Well-Known Member

• Apr 23, 2010

• #4

All you wanted to know about cap values. Great write up.
**broken link removed**

 

J

jack0987

Member

• Apr 23, 2010

• #5

Thankyou Mikebits. I will read it.
What do you think of my using the 22pf in place of the 20pf for now to get my microcontroller ticking?
will it change the timing of the 4mh crystal I am using?

 

Mikebits

Well-Known Member

• Apr 24, 2010

• #6

Yeah I think you have 22pf caps with 10% tolerance. Worst case is I am wrong and they don't work

And 22pf caps will work just fine for your application.

Dean Huster and Van Roon wrote a masterpiece with this paper as they demystify cap markings.

 

Last edited: Apr 24, 2010

J

jack0987

Member

• Apr 24, 2010

• #7

Thanks again Mikebits.
I was just reading your suggested material.
I think they are 22pf too.
Will it alter the frequency? Do they even make a 20pf?
Oh, one last thing. Should I cut the leads to be as short as possible?

 

Last edited: Apr 24, 2010

Mikebits

Well-Known Member

• Apr 24, 2010

• #8

Keep the cap leads as short as possible. The 2pf difference will not matter. Go for it

 

J

jack0987

Member

• Apr 24, 2010

• #9

That's it. Thanks.