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These look like capacitors, but they're not labeled and I'm not quite sure what to make of them.

Enter image description here

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The component is a “ceramic resonator” and the capacitors are internal to the component.

Resonators can be used in place of crystals in applications where the accuracy is not very important. Typically a resonator might have an accuracy of something like +/-1% or 0.5% versus tens of ppm for an inexpensive crystal.

The temperature and aging drifts are also worse. The advantages include less issue with drive level and faster (and more reliable) start-up. They may be cheaper.

The part number on the original schematics reportedly refers to a Murata CSTCE16M0V53-R0, though some clones use a crystal and external load capacitors. That’s a 16MHz +/-0.5% initial tolerance part with 15pF load caps.

Photo from Digikey: enter image description here

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    \$\begingroup\$ Some automotive-related manufacturer of devices uses a 0.5% ceramic resonator as the clock source for a CAN interface. I have had the "privilege" to debug such a system... At least I discovered Sigrok. \$\endgroup\$ – Peter Mortensen Mar 30 at 2:30
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If you look carefully, the crystal and capacitors form one component in the schematic.
It is a resonator, a package where the crystal has integrated capacitors. For that reason the capacitor values are not explicitly given (maybe they're in the datasheet of the resonator).

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Blocking capacitors prevent D.C from affecting the performance/operation of the resonator(clock). D.C voltages have a tendency to destroy performance in filters as well. The resonator might operate over a broad range, making specific value capacitors useless in this circuit. Depending on pass bandwidth of the resonator, they probably maintain load impedance at a satisfactory level across the device's operating range.

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  • \$\begingroup\$ Range of what? Frequencies? Voltages? Temperatures? \$\endgroup\$ – Peter Mortensen Mar 30 at 2:34
  • \$\begingroup\$ Re "Blocking capacitors prevent DC from affecting the performance/operation of the resonator(clock)": But would they prevent a DC offset from XTAL1 / XTAL2? XTAL2 is the driver, so isn't there a DC voltage offset? From page 50: "Pins XTAL1 and XTAL2 are input and output, respectively, of an inverting amplifier" \$\endgroup\$ – Peter Mortensen Mar 30 at 2:49
  • \$\begingroup\$ I do not have any Arduino devices to play with, or test. The schematic leaves much to the imagination, as the graphics are poor, and not laid out well, where individual components are concerned. \$\endgroup\$ – Ernest Erickson AEC Mar 31 at 18:48
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The resonator is actually the circuit comprised of the crystal on the left and R2 on the right. The two capacitor symbols are shunt to ground to reduce noise and provide resonator stability.

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These two capacitors which are about 220nF plus the crystal oscillator (16MHz) provide the correct timing for the arduino.

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  • \$\begingroup\$ Must be a typo 220nF are to high, a range of 8pf to 22pf is commonly used. Capacity depends on resonator and chip. \$\endgroup\$ – WalterH Mar 31 at 18:16
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3 leg bypass crystal center point grounded

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    \$\begingroup\$ please explain your answer. \$\endgroup\$ – Mike Mar 30 at 5:17

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