What crystals for PIC?

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wannaBinventor

Joined Apr 8, 2010
180
I've got some PIC equipment inbound, but I believe I'll need some crystals.

What Hz should I order?

I already have some PIC16F84s -- but I'm sure I'll branch out to some others so please consider that when you advise me on crystal choices.
 

SgtWookie

Joined Jul 17, 2007
22,230
Well, many of the newer PICs have internal oscillators that are factory set to have about 1% accuracy. Unless you really need better accuracy, or faster clock speeds than the internal oscillator is able to provide, I'd stick with the internal oscillator; as it will save you a couple of I/O pins and the extra board space.

Besides, crystals are somewhat fragile. Drop them from a couple of feet on a hard surface and they're toast. Ask me how I know this. :rolleyes:

You might eventually want to run things at 10MHz or 20MHz. If you're just tinkering right now, don't worry about it too much. Some speeds come in handy for communications with RS-232 - if you still have a computer or devices that support it. Best not to develop anything new for RS232 though; it's going the way of the dinosaur. USB 2.0 or FireWire is much faster.
 

Markd77

Joined Sep 7, 2009
2,806
You could get some 32.768KHZ ones if you want to do some low power accurate timing work. It divides down nicely into seconds.
 

t06afre

Joined May 11, 2009
5,934
The data sheet will give you this information. Follow the recommendation in the data sheet and you will be safe. Instead of using the old PIC16F84 you should consider newer variants. They cost less and have more onboard functions. Like more timers,SPI, and PWM
 

rjenkins

Joined Nov 6, 2005
1,013
We manufacture gear using various PICs.

Depending on the speed and accuracy of the specific design, we have used 4MHz, 9.8304MHz, 10MHz and 20MHz quartz crystals, generally in HC49/4 (low height) cans. These need load caps from either end to 0V, we use 20pF for 4MHz, 10pF for 10MHz and 6.8pF for 20MHz.

We also use three terminal ceramic resonators for 4MHz, 4.91MHz and 10MHz. These have the caps built in, you just ground the middle pin. They are not quite as accurate as crystals, but still good while cheaper & easier to assemble.

The actual frequency to select depends on the rating of the PIC itself and choice of oscillator configuration.
 

BMorse

Joined Sep 26, 2009
2,675
I've got some PIC equipment inbound, but I believe I'll need some crystals.

What Hz should I order?

I already have some PIC16F84s -- but I'm sure I'll branch out to some others so please consider that when you advise me on crystal choices.

The crystals you select should depend on he frequency required for the microcontroller, for the F84's I have seen them rated at 4mhz, to 20Mhz, the newer pic replacements for the F84, which is the Pic16F628A's have built in oscillators, and you can use up to 20 mhz for external....

B. Morse
 

retched

Joined Dec 5, 2009
5,207
You can also get a programmable osc. This gives you the accuracy and the variability.

The osc start at a nominal frequency but in the first few instructions in your PIC, you can tell it at which speed to oscillate.
 

davebee

Joined Oct 22, 2008
540
A microprocessor can draw much more current if it is run at a higher speed, and will get hotter, and can emit more radio frequency interference.

So for battery powered devices or for generally better design, it's better to run a microprocessor slower, if the project doesn't need higher speed.
 

CVMichael

Joined Aug 3, 2007
419
the newer pic replacements for the F84, which is the Pic16F628A's have built in oscillators, and you can use up to 20 mhz for external....
Actually the replacement for PIC16F84 is PIC16F88 (see this), which has up to 8MHz internal oscillator, and up to 20MHz external.

You can also get a programmable osc.
That would be this: http://forum.allaboutcircuits.com/showthread.php?t=38616 ;)

A microprocessor can draw much more current if it is run at a higher speed, and will get hotter
I run ALL my PICs at maximum frequency, I even overclocked from 20MHz to 24MHz, and it did not get even warm !
I don't know what PICs you have experience with, but I would get worried if it wams up even a little bit...
 
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BMorse

Joined Sep 26, 2009
2,675
Actually the replacement for PIC16F84 is PIC16F88 (see this), which has up to 8MHz internal oscillator, and up to 20MHz external.


That would be this: http://forum.allaboutcircuits.com/showthread.php?t=38616 ;)


I run ALL my PICs at maximum frequency, I even overclocked from 20MHz to 24MHz, and it did not get even worm !
I don't know what PICs you have experience with, but I would get worried if it worms up even a little bit...
wow you can google stuff :rolleyes:, but still can't spell warms... unless you are saying your pics have worms :eek:

B. Morse
 

CVMichael

Joined Aug 3, 2007
419
but still can't spell warms...
LOL... Well, English is my second language, my original language does not need spelling... and besides, the spell checker in Firefox did not complain, so I assumed it's correct :D, they should also add "words in context" checker :D

I edited my post and corrected the "worms" ;)

Thanks
 

BMorse

Joined Sep 26, 2009
2,675
LOL... Well, English is my second language, my original language does not need spelling... and besides, the spell checker in Firefox did not complain, so I assumed it's correct :D, they should also add "words in context" checker :D

I edited my post and corrected the "worms" ;)

Thanks

Is your first language French??? I hope you didn't take offense to my comment I was just playing around....;)

B. Morse
 

CVMichael

Joined Aug 3, 2007
419
I'm Romanian... we spell words as we hear them, so "spelling" was a completely new thing for me.

No, I did not take offense, I laughed at my mistake also :)

How do you debug a worm infected system:p
LOL :D

At least you have a lure to go catch some fish :)

[edit]
It's starting to get quite embarrassing now... so I will stop posting for now
 
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