# crystal and capacitor selection for project

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#### MrDEB

##### Well-Known Member
ordering parts for the air cannon project but in a quandry about crystal and capacitors.
my code :
Device = 18F452
Clock = 40
Config Osc = HSPLL

I almost ordered 40mhz crystals but learned that using the HSPLL it multiplies by 4 so I need 10mhz crystal.
but which one?
At Mouser it has two types HC49us or CSA-309
am assuming one is more accurate??
then capacitors
ceramic 22pf ok or is there a better choice?

#### Janis1279

##### Member
The both crystal types looks very similar.

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• crystals.JPG
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#### be80be

##### Well-Known Member
HC49us That's a good crystal Would be nice if you could clock a 40 mhz to 160 but you
can't lol I did that with a 20 and felt dum and got me some 10 mhz crystals

22pf will work fine.

#### MrDEB

##### Well-Known Member
PIC chips are they interchangable?

looking at the 18F4520 and the 18F452
both look basically the same but the 4520 has an internal osc up to 32mhz (pretty sure as I am newbi at this)
ordered samples from Microchip to try out.
working on flow charts as to the operation of the air cannon data acquisition.
two IR sensors for the muzzle velocity measurements
two slot interrupters (wind speed and wind direction)
air chamber pressure (on Ebay I scored an expensive pressure transducer for $18.50 including shipping) Called manfacture and the unit DSY-150 sells for$200+
unit is brand new, never used. just hope it works.
locating different code snippets to try out.
One question about LCD interfacing= ordered several 16 x 2 as well as 20x4.
can I use the same LCD.bas to operate either??
I need to research this aspect of project.

#### fermat7

##### Member
capacitors r used to exchange energy...
22pF works good...
for the accuracy you can find it easily when reading the crystal frequency!!..

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