Question on Ceramic Resonators

[bigal_scorpio]

Hi to all,

I just realised that though I have a few different Ceramic Resonators, I don't know how to use them!

I was pondering building a new PIC circuit and though I didn't have the correct value crystal I had a C.R of the correct value.

Then came the puzzle, I have always connected PICs the same way with crystals across Osc1 and Osc2 then grounding both through small caps.

Then I remembered reading that C.Rs don't need the caps that crystals need, so do I just connect the C.R across Osc1 and Osc2 and job done? Or do I need some other connection to the C.R?

Then it struck me that there are 2 pin and 3 pin versions of the C.R! Now I'm even more puzzled.

I tried Googling for an explanation but all I found was why one was better than the other and how they could soon both be replaced by something new (silicon oscillators)! Just something else to confuse me.

So can anyone tell me how to use C.Rs on a PIC explaining both 2 and 3 leg varieties? Or point me to a site that can?

Thanks for looking..............Al

 

[picbits]

Get a 3 lead CR as these have the caps built in.

Center pin to ground and the other two to OSC1 OSC2

If you use a 2 pin CR then you still need caps as you would do with a Crystal.

 

[picbits]

2 Pin CR treat as a Crystal (without caps) - you will need caps with these.
3 Pin CR treat as a Crystal with inbuilt caps.

 

[bigal_scorpio]

Thanks for the quick reply Picbits!

Just one more quick question?

Same value caps for C.Rs as Crystals or is there some way of working it out?

Thanks...............Al

 

[picbits]

Not a clue - I always use the 3 pin variety.

Maybe have a chopsy at the datasheet and see what they suggest. If not then I'd start with the suggested caps for the Crystal.

 

[picbits]

Had a quick look at the 3 pin datasheet. The 4Mhz ones I have use 20pF caps.

 

[picbits]

The 10Mhz ones I have use 30pF caps ........

 

[bigal_scorpio]

Cheers mate,

Thanks for all the help mate, I'm off to make some magic smoke now with my new found information

Al