Creative Commons images are CC BY-NC-SA 3.0

### \$ 0.95

added to your
shopping cart

 quantity In stock 250+ in stock 0.95 1+ units 0.90 25+ units 0.86 100+ units
Need larger quantities?
Check out our Volume Sales program

Description: Standard frequency crystals - use these crystals to provide a clock input to your microprocessor. Rated at 20pF capacitance and +/- 50ppm stability. Low profile HC49/US Package.

## Customer Comments

• Looking at the Arduino schematic I see they use a large 1M resistor in the simple oscillator circuit. On others from Sparkfun the resistor is omitted. I’ve looked on the web for about an hour, can someone comment on the reason for the resistor. Thanks

• I noticed that as well but since this hasn’t been answered in 3 years I doubt it will be at all.

• Thankfully, there’s still the internet - there’s several sites that explain its most likely use, but I’ll citeto Mike@Adafruit’s explanation;

Putting a crystal in parallel with the feedback resistor creates a path where signals at a certain frequency are phase-shifted 180 degrees. Adding that to the inversion (equivalent to another 180 degree phase shift) gives you a 360 degree shift. That turns the negative feedback to positive feedback for that specific frequency. Positive feedback makes signals increase exponentially until they hit the inverter’s gain limits.
The upshot is a (hopefully) self-starting oscillator

• This is not at all what that resistor is for. The phase shift arises from a single capacitor in the feedback path of the oscillatory circuit. The second capacitor exists for reasons relating to RF reflection that I will admit I do not understand enough to explain. The feedback resistor is in place for biasing the internal amplifier. The circuit is inherently unstable and will oscillate.

• Yes, I am wondering the same thing!

• Wow! I just did the math… it comes out to about +/- 3.12ps (for +/-50ppm)! That’s 3 trillionths of a second. And for comparison: light can travel ~1mm in that time.

• Wow! My jaw just dropped to the floor.

• Best crystal to use with a ATMega 328.

• Is there a datasheet for this?

• Is there a datasheet for this?

• Is the load capacitance of this Crystal 20pF? If so, wouldn’t it need 2, 30pF, caps, rather than the 22pF that people are recommending?

• What type of output do these have? I need a square wave oscillator with 50% duty cycle. Would I need an inverter circuit with this crystal to accomplish this? Other implementation?

• You need a crystal oscillator circuit to work with these. Most microcotrollers already have the circuitry in them, they just need the eternal crystal to set the timing.

• My question is: which part is right in Eagle file? HC49US or HC49U-V? Thanks.
BTW, I’ve used this on my arduino breadboard version. Perfect! I used 22pF capacitors for it.

• Never mind. It says HC49/US in description.

• Where did you find the HC49/US in Eagle? I can’t find it at all. I see HC49/S and HC49U but they are different.

• Search for that exactly HC49US it is in the sparkfun eagle footprint library.

• what does the letter at the end of 16.000 (ex 16.000N in the picture) indicate? I have two 16MHz crystals in my possession, one says 16.000N and the other 16.000R…and I can’t figure out for the life of me what it means or if I should even care

• The datasheet doesn’t specify marking codes, so we don’t know. It may be a date code, temperature rating, etc.

• I found this but was it the right one?

• These are great with Atmega328 :)
But a datasheet would be nice, anybody know where to find it?

• Do these come with the matching capacitors? If not, do you sell them separately? I looked around but couldn’t find them..

• A bit late, but you have to buy the 22pf load caps separately.
They are one of the first thing under Components>General

• How many do I need? Please reply quickly, as I need to order some things soon…

• 2 caps per crystal.

• Darn! I only ordered one! Guess I’ll have to drop by the local RadioShack soon…

• never mind

• what is the load capacitance?

## Customer Reviews

No reviews yet.

SparkFun is an online retail store that sells the bits and pieces to make your electronics projects possible. Whether it's a robot that can cook your breakfast or a GPS cat tracking device, our products and resources are designed to make the world of electronics more accessible.

In addition to products, SparkFun also offers classes and online tutorials to help educate individuals in the wonderful world of embedded electronics.